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PLOS ONE logoLink to PLOS ONE
. 2021 Jul 9;16(7):e0254525. doi: 10.1371/journal.pone.0254525

COVID-19 incidence and mortality in non-dialysis chronic kidney disease patients

Dino Gibertoni 1,*,#, Chiara Reno 1,#, Paola Rucci 1, Maria Pia Fantini 1, Andrea Buscaroli 2, Giovanni Mosconi 3,4, Angelo Rigotti 5, Antonio Giudicissi 4, Emanuele Mambelli 5, Matteo Righini 2, Loretta Zambianchi 3, Antonio Santoro 6, Francesca Bravi 7, Mattia Altini 7
Editor: Giuseppe Remuzzi8
PMCID: PMC8270438  PMID: 34242368

Abstract

Many studies reported a higher risk of COVID-19 disease among patients on dialysis or with kidney transplantation, and the poor outcome of COVID-19 in these patients. Patients in conservative management for chronic kidney disease (CKD) have received attention only recently, therefore less is known about how COVID-19 affects this population. The aim of this study was to provide evidence on COVID-19 incidence and mortality in CKD patients followed up in an integrated healthcare program and in the population living in the same catchment area. The study population included CKD patients recruited in the Emilia-Romagna Prevention of Progressive Renal Insufficiency (PIRP) project, followed up in the 4 nephrology units (Ravenna, Forlì, Cesena and Rimini) of the Romagna Local Health Authority (Italy) and alive at 1.01.2020. We estimated the incidence of COVID-19, its related mortality and the excess mortality within this PIRP cohort as of 31.07.2020. COVID-19 incidence in CKD patients was 4.09% (193/4,716 patients), while in the general population it was 0.46% (5,195/1,125,574). The crude mortality rate among CKD patients with COVID-19 was 44.6% (86/193), compared to 4.7% (215/4,523) in CKD patients without COVID-19. The excess mortality of March-April 2020 was +69.8% than the average mortality of March-April 2015–19 in the PIRP cohort. In a cohort mostly including regularly followed up CKD patients, the incidence of COVID-19 among CKD patients was strongly related to the spread of the infection in the community, while its lethality is associated with the underlying kidney condition and comorbidities. COVID-19 related mortality was about ten times higher than that of CKD patients without COVID. For this reason, it is urgent to offer a direct protection to CKD patients by prioritizing their vaccination.

Introduction

The outbreak of a new epidemic carries along the urgent need to understand how the different segments of the population are affected in order to develop appropriate public health strategies to protect vulnerable subgroups and to support clinical management and decision-making. The emergence of a novel coronavirus in Wuhan, China, in December 2019, isolated in early January 2020 and later on in February named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causing coronavirus disease 2019 (COVID-19) [1] prompted global investigations on the effects and clinical manifestations of the virus and, on the other side, on the possible risk factors for a severe disease. The virus has spread at an impressive and alarming speed around the world and on March 11, 2020, the World Health Organization (WHO) declared COVID-19 a pandemic [2]. Italy has been one of the first European countries to be affected by the pandemic and during the first wave Northern regions were markedly involved. However, even within the same region, a different geographical pattern of virus spread occurred depending on the distance from disease hotspots, thus leading areas of the same territory to suffer the effects of the pandemic with different timings [3].

Evidence accumulating over time showed that, although SARS-CoV-2 infection primarily causes respiratory illness with highly variable clinical manifestations, other organs may be damaged by the virus, the kidney being one of the main site of complications [4]. Patients requiring dialysis and kidney transplant recipients have been first identified as a subgroup at higher risk for poor outcomes, and often present atypical clinical features that constitute an additional challenge [5]. Only recently chronic kidney disease (CKD) has been demonstrated to be a key risk factor for COVID-19 mortality as well, with a clear association between the level of dysfunction and mortality rate [68]. Specifically, in the recently published OpenSAFELY project, based on 17 million patients [6, 7], dialysis (adjusted hazard ratio (aHR) = 3.69), organ transplant (aHR = 3.53) and stage of CKD (aHR = 2.52 for patients with eGFR <30 mL/min/1.73 m2) were three of the four comorbidities associated with the highest mortality risk from COVID-19. The risk associated with low eGFR was higher than the risk associated with diabetes mellitus (aHR range 1.31–1.95, depending upon the level of glycaemic control) or chronic heart disease (aHR = 1.17). In another recent publication of the Global Burden of Disease collaboration, CKD was reported as the most prevalent risk factor for severe COVID-19 [9]. The high prevalence of CKD among COVID-19 cases and their elevated risk of mortality calls for urgent action on this vulnerable population [10]. To date, evidence from the literature on this topic is based on hospitalized patients with COVID-19 and there is a lack of information on the incidence of COVID-19 from longitudinal studies conducted on CKD patients. To fill this gap, our study aimed at estimating the incidence and mortality related to COVID-19 in a large cohort of CKD patients enrolled in the Emilia-Romagna region project “Prevenzione insufficienza renale progressiva” (PIRP).

Our specific aims were: 1) to estimate the incidence of COVID-19 in CKD patients; 2) to identify predictors of the incidence of COVID-19 among CKD patients; 3) to compare the mortality of CKD patients with and without COVID-19; 4) to analyze predictors of COVID-19 mortality among CKD patients; 5) to estimate the excess mortality of CKD patients during the first wave of COVID-19 pandemic compared to the equivalent period in 2015–19; 6) to compare in-hospital COVID-19 mortality between CKD and non-CKD patients.

Materials and methods

The study was approved by the Romagna Ethics Committee on 9.10.2020 n° 7843/2020. Consent was not required because data were analyzed anonymously.

Study population

The study population includes CKD patients enrolled in the PIRP project and residing in the Romagna Local Health Authority (AUSL Romagna) catchment area, that encompasses the provinces of Ravenna, Forlì-Cesena and Rimini.

PIRP is a project established in 2004 and funded by the Emilia-Romagna region that is devised to timely intercept and follow up people with chronic kidney disease with the aim to delay their progression and prevent kidney failure [11]. The project started in 2004 and to date includes more than 31,000 patients and 130,000 visits, being one of the largest European registries on CKD patients [12]. Patients followed up in PIRP are adult patients with CKD-EPI stage 3a to 5, or patients at an earlier CKD stage with albuminuria/proteinuria or abnormalities detected by renal imaging, with or without other comorbidities [11]. Patients who reach ESKD (dialysis or transplant) exit the project. Considering that the most recent estimate of CKD stage 3–5 prevalence in Italy was 2.89% [13], and that the prevalence of PIRP patients living in the AUSL Romagna area was 0.84%, the PIRP project gathered about 30% of CKD stage 3–5 patients. The database of the project includes information about ambulatory visits, laboratory data, drug prescriptions, and is linked with the official regional databases of dialysis and transplantation, the hospital discharge records (HDR) database, and the mortality registry (“Registro Mortalità”—ReM). Patients extracted for the present study were those alive on 01.01.2020 and in pre-dialysis CKD stages. They comprised both patients under periodical nephrological follow-up and those referred back to their general practitioner because they had a less severe degree of CKD, or to other specialists.

AUSL Romagna is a Local Health Authority of Northern Italy located in Emilia-Romagna region with a catchment area of 1,125,474 inhabitants as of January 1, 2020 and a population density of 220.6 per km2. It comprises a high population density plain and seaside area, with several close and connected small- and middle-sized urban areas, and a low population density mountain area. The four nephrology units participating in the PIRP project and operating in the hospitals of Ravenna, Forlì, Cesena and Rimini were involved in the present study. They share common therapeutic guidelines for the treatment of CKD patients and have the same care pathway.

Data sources

PIRP patients with COVID-19 disease were extracted from the HDR database or from the database of SARS CoV-2 positive patients confirmed by RT-PCR for the period between January 1, 2020 and July 31, 2020. The COVID-19 onset date was the admission date for those hospitalized and the referral date for those not hospitalized. Mortality in the PIRP cohort was obtained from the mortality registry (ReM) database, which includes deaths occurred both in- and out-of-hospitals and information on the causes of death.

Information on SARS-CoV-2 infection in the general population was obtained from the official figures provided by the Italian National Ministry of Health and released by the Civil Protection Department (CPD) on their website www.protezionecivile.gov.it. Residents as of January 1, 2020 were retrieved from the Italian National Institute of Statistics website (http://demo.istat.it). Mortality in the general population was retrieved from official data on COVID-19 released by AUSL Romagna up to October 25, 2020 [14].

Data on patients’ comorbid conditions were retrieved from the HDR database. Specifically, cardiovascular diseases, COPD, tumors and liver disease were identified using the Elixhauser algorithm [15] by searching for all the diagnoses reported in HDR of 2017–19. Dementia was assessed by searching for a specific subset of diagnosis codes in the HDR database, and diabetes by combining data from the clinical history of the PIRP registry and the HDR database (Table A in S1 Appendix). eGFR was estimated from patients’ most recent creatinine values using the CKD-EPI equation [16] and CKD stages were defined according to KDIGO guideline.

Statistical analysis

Clinical and demographic patients’ characteristics were summarized using mean±SD or absolute and relative frequencies according to the type of variable. Multivariable logistic regression was used to identify PIRP patients’ characteristics independently associated with COVID-19 disease.

COVID-19 related mortality rates were compared among CKD stages, sex and geographical area. Survival in subgroups of CKD patients was investigated using Kaplan-Meier survival analysis and log-rank tests. In this analysis, the period of COVID-19 onset was used as predictor to test whether the risk of mortality was higher in the first weeks of the pandemic.

The excess mortality in CKD patients was estimated for the year 2020. To this purpose, age and sex adjusted mortality rates were computed for the period January-July of each year between 2015 to 2020, using the age/sex distribution of the PIRP cohort on January 1, 2015. The excess mortality rate was then computed as the ratio of the adjusted mortality rate of 2020 to the mean of the adjusted mortality rates for the years 2015–19.

In-hospital COVID-19 mortality was compared between CKD patients and non-CKD patients by searching for all individuals with a hospital admission due to COVID-19 in the period 1 January– 31 July 2020 and performing a multivariable logistic regression. In this regression, age, sex, province and comorbidities assessed during hospital admissions of 2018–19 were included as potential confounders.

All analyses were carried out using Stata v.15.1, and the significance level was set to p<0.05.

Results

Characteristics of the study cohort

In the study area, 4716 patients followed up in the PIRP project were alive on January 1, 2020. Mean age was 76.2±11.6 years, males were 65.4%, eGFR was 38.1±15.8 ml/min/1.73m2. 33.8% had diabetes, 21.0% cardio-vascular comorbidities and 5.1% COPD. The characteristics of CKD patients by CKD-EPI stage and by province are reported in the (Tables B-C in S1 Appendix).

Incidence of COVID-19

As of July 31, 2020, 193/4716 CKD patients had COVID-19 disease, with a 4.09% incidence. Among these 184/193 (95.4%) were hospitalized. In the general population of AUSL Romagna, the incidence of COVID-19 cases was 0.46%. In the province of Rimini there was the highest incidence of COVID-19, both in the general population (0.66%) and among CKD patients (5.35%), and in Ravenna the lowest (0.29% and 2.58% respectively).

CKD patients affected by COVID-19 were on average older than those unaffected (80.8 vs. 76.0 years), had a poorer kidney function (eGFR = 32.5 vs. 38.3 mL/min/1.73m2) and a higher prevalence of cardiovascular comorbidities, chronic obstructive pulmonary disease (COPD) and tumors (Table 1). Multivariable logistic regression confirmed that patients with CKD-EPI stage 4 (OR = 1.562), older age (OR = 1.033), cardiovascular comorbidities (OR = 1.822), COPD (OR = 1.906) and tumors (OR = 1.631) were more likely to have COVID-19. After adjustment for covariates, patients living in the Ravenna province (OR = 0.491) and those living in the Forlì-Cesena province (OR = 0.662) were less likely to be affected by COVID-19 disease than those living in Rimini.

Table 1. Characteristics of CKD patients with and without COVID-19 disease, and predictors of COVID-19.

With COVID-19 (n = 193) Without COVID-19 (n = 4523) OR (95% CI) p-value
Age at January 1, 2020, mean±SD 80.8±8.9 76.0±11.7 1.033 (1.014–1.053) 0.001
Males, n(%) 123(63.7) 2963(65.5) 1.205 (0.872–1.666) 0.258
Immigrants, n(%) 6(3.1) 170(3.8) 1.301 (0.508–3.327) 0.583
Province, n(%)
    Ravenna 22(11.4) 830(18.3) 0.491 (0.303–0.796) 0.004
    Forlì-Cesena 62(32.1) 1765(39.0) 0.662 (0.472–0.928) 0.017
    Rimini 109(56.5) 1928(42.6) Ref.
BMI (kg/m2), mean±SD 28.4±5.1 28.0±4.8
    <25 51(27.4) 1240(27.8) Ref.
    25–29.99 69(37.1) 1912(42.8) 0.874 (0.598–1.279) 0.489
    30–34.99 47(25.3) 969(21.7) 1.197 (0.783–1.829) 0.406
    ≥35 19(10.2) 343(7.7) 1.424 (0.803–2.526) 0.226
eGFR (mL/min/1.73m2), mean±SD 32.5±12.1 38.3±15.9
    CKD-EPI stage 1–2 4(2.1) 336(7.4) 0.575 (0.203–1.628) 0.298
    CKD-EPI stage 3a 25(12.9) 989(21.9) 0.728 (0.447–1.187) 0.204
    CKD-EPI stage 3b 73(37.8) 1772(39.2) Ref.
    CKD-EPI stage 4 84(43.5) 1256(27.8) 1.562 (1.116–2.186) 0.009
    CKD-EPI stage 5 7(3.6) 169(3.7) 1.090 (0.485–2.449) 0.834
Primary kidney disease, n(%)
    Hypertensive nephropathy 150(77.7) 3124(69.1)
    Diabetic nephropathy 17(8.8) 415(9.2)
    Polycystic kidney 3(1.6) 95(2.1)
    Pyelonephritis 2(1.0) 227(5.0)
    Glomerulonephritis 4(2.1) 156(3.4)
    Single kidney 7(3.6) 219(4.8)
    Unknown nephropathy 8(4.2) 225(5.0)
    Rare nephropathies 2(1.0) 62(1.4)
Diabetes, n(%) 69(35.7) 1500(33.2) 1.033 (0.748–1.427) 0.845
Cardiovascular comorbidities, n(%) 77(39.9) 911(20.2) 1.822 (1.311–2.533) <0.001
COPD, n(%) 26(13.5) 213(4.7) 1.906 (1.182–3.072) 0.008
Tumors, n(%) 21(10.9) 300(6.6) 1.631 (1.002–2.655) 0.049
Liver disease, n(%) 2(1.0) 41(0.9) - -
Dementia, n(%) 10(5.2) 96(2.1) 1.650 (0.827–3.292) 0.155

Mortality

Predictors of COVID-19 mortality in CKD patients

Overall, 301/4716 (6.4%) CKD patients died up to July 31, 2020 (Table 2). The crude mortality rate in CKD patients with COVID-19 (86/193, 44.6%) was almost tenfold than in those without COVID-19 (215/4523, 4.7%). COVID-19 mortality in CKD patients was higher among those in CKD-EPI stage 4 (54.8%) and was consistently higher than in patients without COVID-19 in all CKD stages. The CMR of CKD patients with COVID-19 did not show remarkable differences between sex and among provinces.

Table 2. Mortality in CKD patients with and without COVID-19 disease.
All CKD patients No COVID-19 disease COVID-19 disease
Number of deaths Crude mortality rate Number of deaths Crude mortality rate Number of deaths Crude mortality rate
Overall population 301/4716 6.38% 215/4523 4.75% 86/193 44.56%
CKD-EPI stage
    1–2 3/340 0.88% 2/336 0.60% 1/4 25.00%
    3a 30/1014 2.96% 23/989 2.33% 7/25 28.00%
    3b 109/1845 5.91% 80/1772 4.51% 29/73 39.73%
    4 138/1340 10.30% 92/1256 7.32% 46/84 54.76%
    5 21/176 11.93% 18/169 10.65% 3/7 42.86%
Males 175/3086 5.67% 121/2963 4.08% 54/123 43.90%
Females 126/1630 7.73% 94/1560 6.03% 32/70 45.71%
Province
    Ravenna 53/852 6.22% 43/830 5.18% 10/22 45.45%
    Forlì-Cesena 121/1827 6.62% 92/1765 5.21% 29/62 46.77%
    Rimini 127/2037 6.23% 80/1928 4.15% 47/109 43.12%

Factors significantly associated with higher COVID-19 mortality in CKD patients in univariate survival analysis (Fig 1 and Table D in S1 Appendix) were older age, most severe stages of CKD, dementia and SARS-CoV-2 infection in the early phase of the pandemic. Notably, the large majority of patients (71.4%) who were infected between March 8–21, 2020 died.

Fig 1. Cumulative hazards of COVID-19 related mortality.

Fig 1

(A) By period of onset of the disease. (B) By CKD stage.

The cause of death was reported in the mortality registry for 84/86 CKD patients and was COVID-19 in 30/84 (35.7%) cases; in 7/84 (8.3%) cases pneumonia and respiratory diseases, and in 4/84 (4.8%) cases infectious diseases were reported. However, 61/86 (70.9%) CKD patients died during the hospitalization for COVID-19 disease. Acute kidney injury (AKI) was developed by 21/193 (10.9%) patients, of whom 11/21 (52.4%) died. Only 4/193 (2.1%) underwent hemodialysis treatment during their COVID hospitalization, and 2 of them had a concurrent AKI.

To enable the comparison with hemodialysis patients, for whom the CMR in an Italian cohort is available as of April 23, 2020 [17], we computed the CMR of CKD patients at the same date. Results indicate that the CMR was slightly lower in CKD patients than in hemodialysis patients (37.8% vs. 41.5%).

Excess mortality in CKD patients

In the overall PIRP cohort, mortality in January-July of 2020 increased by +17.7% with respect to the average mortality observed in the same period in 2015–19 (Table 3). This increase corresponds to 77 more deaths more than expected. The excess mortality had a peak in the months of March and April, when 58 more deaths (+69.8%) were observed. In January-February, before the pandemic outbreak, a slight decrease of mortality was recorded, while from May to July an excess of 22 deaths (+10.1%) occurred.

Table 3. Excess mortality of CKD patients in 2020 with respect to the average mortality of 2015–19.
Number of deaths Adjusted mortality rates Excess mortality (%) Excess mortality (n)
Period Average 2015–19 2020 2020 COVID disease 2020 no COVID disease- Average 2015–19 2020
January- February 82 79 0 79 1.82% 1.53% -15.9% -3
March-April 65 123 51 72 1.44% 2.44% +69.8% 58
May-July 80 102 35 67 1.80% 1.98% +10.1% 22
January-July 227 304 86 218 5.06% 5.95% +17.7% 77

Predictors of in-hospital COVID-19 mortality in CKD patients vs. non-CKD patients

The multivariable logistic regression model of in-hospital COVID-19 mortality revealed that, after adjusting for age, sex, area and comorbidities, CKD patients had a 43.8% higher risk of dying than the other hospitalized individuals (Table 4 and Table E in S1 Appendix).

Table 4. Predictors of in-hospital COVID-19 mortality.
Odds Ratio 95% CI p-value
CKD (enrolled in PIRP) 1.438 1.046–1.978 0.025
Age, years 1.069 1.062–1.076 0.000
Males 1.414 1.226–1.631 0.000
COPD 1.038 0.785–1.371 0.794
Liver disease 1.382 0.763–2.505 0.286
Dementia 1.792 1.318–2.437 0.000
Cardiovascular comorb. 1.282 1.054–1.559 0.013
Diabetes 1.198 0.915–1.569 0.188
Tumors 1.685 1.317–2.154 0.000
Province
    Ravenna 0.870 0.730–1.037 0.120
    Forlì-Cesena 1.203 1.023–1.416 0.026
    Rimini Ref.

Discussion

In our cohort involving 4,716 CKD patients in non-dialysis stage, we found a 4.09% incidence of COVID-19 and a related mortality rate of 44.6%. Our results are consistent with evidence from the literature suggesting that CKD patients are on average older and more vulnerable to SARS-CoV-2 infection [18] and that CKD is an underlying condition that increases the risk of severe COVID-19 illness [19].

Older age, lower GFR, cardiovascular comorbidities and COPD were associated with a higher likelihood of SARS-CoV-2 infection, confirming previous findings [20, 21]. After adjusting for these conditions, the geographical area remained an independent risk factor, underscoring that the incidence of COVID-19 in CKD patients reflects that of the general population of the same area. Specifically, the Rimini province was exposed to an early intense epidemic flow originating from the neighboring hotspot area of Pesaro (Marche region), which happened before the national lockdown enforced on March 9, 2020 by the Italian Government [22] when healthcare services had to face an exceedingly large number of people referring to hospitals and emergency wards. The incidence of COVID-19 in CKD patients differed among the provinces examined in our study, although access of CKD patients to ambulatory facilities was similar and based on a standardized care pathway [11] even during the pandemic period.

It must be underlined that our data relate to the first phase of the pandemic, from February to July 2020, when no screening program for vulnerable categories was enforced to identify and trace COVID-19. As CKD patients are mostly old and multimorbid, they are particularly at risk to have symptomatic COVID-19 disease, therefore it is likely that they had been relatively more tested than the general population in that phase of the pandemic. Moreover, patients of our cohort are routinely followed up in a prevention program and are aware of their frail condition, which could have enhanced their propensity to be timely checked for COVID-19.

The high risk of COVID-19 mortality in CKD patients was confirmed by several comparisons carried out in this study. The crude mortality rate of 44.6% was of similar magnitude to that observed in hemodialysis patients treated in the dialysis units of the Emilia-Romagna region [17] and higher than the 25–30% range reported for people older than 70 years in Italy [23, 24] and the 32.9% reported for CKD patients in the German Lean European Open Survey [25].

Lastly, in-hospital mortality was significantly higher than that of non-CKD patients hospitalized for COVID-19 in the same area and period. The CMR was very similar across geographical areas, regardless of the different incidence rates. In fact, once COVID-19 disease is established, CKD patients have high mortality rates because the disease severely affects their already impaired kidney function [4]. These figures consistently underscore the high vulnerability of CKD patients to COVID-19, related to multiple factors [26, 27], and the need to protect this segment of the population.

Another way to look at the COVID-19 death toll on CKD patients is to examine the excess mortality. This measure is free of the potential biases due to incorrect or lacking attribution of the COVID-19 disease to subjects, and as such it allows to estimate the impact of COVID-19 on the overall mortality. CKD patients experienced in the period February 24 –April 30, 2020 an excess mortality of +69.8%, while in the same interval the excess mortality rates of the general population of AUSL Romagna aged 75 years or more were lower [3]. As of July 31, the total excess deaths among CKD patients were 77, and the number of deaths among CKD patients with COVID was 86, being COVID-19 almost the only determinant of excess mortality. CKD patients without COVID-19 had a slightly lower mortality than expected, which may be a positive side effect of the prevention measures enforced to avoid COVID-19 contagion, combined with the effectiveness of their disease management in the PIRP program.

Our study has several limitations. The study population refers to a specific area of Northern Italy, therefore our findings cannot be generalized to other regions or countries where the pandemic had different spread or other containment measures or treatment options were adopted. The number of COVID-19 cases and deaths is relatively small, which prevented us from conducting multivariable analyses on the predictors of mortality. Information on treatment during hospitalization is not available in hospital discharge records. Our results are based on CKD patients included in a prevention and treatment program which approximately covers 30% of CKD patients in AUSL Romagna catchment area, thus they cannot be generalized to all CKD patients.

However, our focus on a cohort of patients with CKD included in a registry and the availability of high-quality data individually linked to administrative databases represent a strength of our study because most of the available evidence on the effect of COVID-19 in CKD patients is derived from hospitalized patients.

In conclusion, we found that CKD patients in non-dialytic stage exhibit a vulnerability to COVID-19 disease comparable to that of patient on kidney replacement therapy. Despite the presence of effective clinical pathways for CKD patients as the PIRP program, the incidence of COVID-19 is strongly related to the spread of the infection in the community. While efforts are made to contain the outbreak with several non-pharmaceutical interventions and a massive vaccination campaign aimed to achieve herd immunity in the general population (indirect protection), it is urgent to give direct protection to CKD patients through their prompt vaccination. Therefore, it is of crucial importance to carefully develop strategies that target this vulnerable segment of the population at higher risk of severe or fatal outcome both in the current and future vaccination campaigns, taking into account the duration of protection, the emergence of new variants of SARS-CoV-2 and their transmission and lethality potential. In addition, consistent with recent action points outlined by ERA-EDTA council [10], we also advocate the inclusion of CKD patients in clinical trials testing the efficacy of drugs and vaccines to prevent severe COVID-19.

Supporting information

S1 Appendix. Supporting Information, including Tables A, B, C, D and E.

(DOCX)

Data Availability

The datasets generated and/or analysed during the current study are property of a third party that is Emilia-Romagna Regional Health Agency (https://assr.regione.emilia-romagna.it/) and, although they are anonymized, datasets are not publicly available due to the current regulation on privacy. The description of the administrative databases is available from the website https://salute.regione.emilia-romagna.it/siseps/sanita/asa/documentazione. Other researchers can obtain access to the data through a formal request based on a research project to the Romagna Local Health Authority.

Funding Statement

The author(s) received no specific funding for this work.

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Decision Letter 0

Giuseppe Remuzzi

21 Apr 2021

PONE-D-21-06894

COVID-19 incidence and mortality in pre-dialysis chronic kidney disease patients

PLOS ONE

Dear Dr. Gibertoni,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

The manuscript focuses on a topic of potential interest. The study, however, presents several major shortcomings that need to be addressed. To mention some of them, i) concern about the fact that the comparison made between groups seem inappropriate, ii) consider as more appropriate comparison, sick elderly cohort without CKD, iii) unclear whether the PRIP cohort was tested routinely, or more frequently than the general population; iv) concern about the fact that if the cause of death was COVID-19 in only 37.5% of these cases, this may undermine the author main point, i.e. that these patients had excess death due to COVID-19 infection; v) it is difficult to say that CKD was responsible for infection or death in the patients with COVID-19; vi) unclear what is the adjusted r2 for the model of mortality attributed CKD; vii) need to add BMI, ethnicity, social deprivation, liver disease and HIV infection, known risk factors for death in COVID, and assess how do they interact with the model; viii) concern about the fact that the mortality is really high; ix) need to define better the study population; x) unclear whether the admissions to hospital were for COVID-19, or unrelated admissions with incidental tests; xi) concern about the fact that there was no specific research question formulated related to differences between provinces; xii) concern about the fact that the results are described separately for the three provinces included in the region, xiii) concern about the conclusion that the incidence of COVID-19 was higher in CKD patients than in the general population, not justified since there was no universal screening for COVID-19; xiv) need to provide in Table A the distribution over CKD stages; xv) need to explain in the section on mortality the difference between the terms crude mortality rate and case fatality rate.

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Giuseppe Remuzzi

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Reviewer #1: Yes

Reviewer #2: No

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Reviewer #1: Yes

Reviewer #2: No

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Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #2: Yes

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5. Review Comments to the Author

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Reviewer #1: This study describes the incidence and outcome of COVID-19 in a cohort of CKD patients as compared to the general population living in the same region. The main finding is that both the incidence of COVID-19 and the mortality rate were around 10 times higher in CKD patients. This corresponds with the data of the OpenSAFELY study, where CKD was found to be major risk factor for COVID-19 related mortality.

Comments:

1. The results are described separately for the three provinces included in the region. Although there are some differences between the provinces, I doubt whether this affects the analysis for the main study outcomes. There was no specific research question formulated related to differences between provinces. I therefore belief that this aspect gets too much attention in the manuscript. For the primary analyses it suffices to use the entire population. Subsequently, it can be checked whether the main conclusions would change when provinces are analysed separately.

2. The conclusion that the incidence of COVID-19 was higher in CKD patients than in the general population might not be justified since there was no universal screening for COVID-19. It is imaginable that CKD patients have more severe symptoms of COVID-19 and that the diagnosis is more often made than in the general population in which there might be a higher proportion of ‘subclinical’ COVID-19 cases. This issue should be discussed in more detail.

3. In Table A, the main diagnosis in CKD patients is ‘hypertensive nephropathy’. Probably this diagnosis was used for patients who had CKD and were hypertensive. However, since most kidney diseases are accompanied by hypertension, this diagnosis should be reserved for patients in whom no other kidney disease is present and kidney biopsy shows characteristic vascular lesions. In fact, it appears that the underlying cause of CKD was unknown in the majority of patients.

4. Table A should provide the distribution over CKD stages

5. In Table A, the abbreviation BPCO should be explained. (Should be COPD?)

6. From Table 1 it is clear that the incidence of COVID-19 is much higher in CKD patients than in the general population. It is confusing that on P8, L154 it is stated that the proportion of cases in the CKD population was lower than in the general population.

7. In the section on mortality, the authors use the terms crude mortality rate and case fatality rate. They should explanin the difference, if any, or use the same term throughout the manuscript.

8. While the CKD stage is an important predictor of mortality, this is not mentioned in the text on p11.

9. On page 11, line 202 there is referral to Table 6. This should be Table 5.

Reviewer #2: Dr Gibertoni and colleagues present a descriptive study of COVID-19 infection in an Italian cohort, focusing on a subpopulation of patients with CKD and comparing disease incidence and mortality to the general population and to those within the cohort with a + COVID test to those without any test. These are interesting data and the linkage of multiple datasets is commendable. The section on excess mortality is the strongest, and is enlightening. However I am concerned that the comparator groups are inappropriate throughout and the high mortality rate and hospitalisations may be misattributed to CKD as a result, leading to incorrect conclusions have been drawn as a result. A number of the data presented seem to undermine the authors main point.

Major issues:

The biggest issue for me is that the comparisons being made between groups seem inappropriate.

Re: Incidence of COVID19

1. Its not ideal comparing these PRIP patients to the general population. These are clearly very elderly comorbid patients, whereas the general population will include healthy young people and potentially even children. A more appropriate comparison would be a sick elderly cohort without CKD. As a result the incidence data is of limited utility.

2. Were the PRIP cohort test routinely, or more frequently than the general population? Why? what was the rate of testing in each?

Re Cause of Death

1. If the cause of death was covid-19 in only 37.5% of these cases , does this not undermine the authors main point- that these patients had excess death due to COVID19 infection? Is this not compounded by the fact that 25% didn’t even die during the admission with COVID19?

Re: Mortality attributed to CKD

1. The patients with covid-19 were older, had more advanced renal disease, higher rates of CV disease, higher rates of COPD (Table 2 ). It is thus hard to say that CKD was responsible for infection or death here. I also suspect there was non-diagnosed covid19 in the “without covid19 group”.

2. What’s the adjusted r2 for this model? The OR for CV and COPD are rather large – the OR for eGFR is per unit, but very close to 1. How much a difference did this really make? ( what did using CKD stages reveal instead?)

3. BMI, ethnicity, social deprivation, liver disease and HIV infection are known risk factors for death in COVID- are these data available and how do they interact with the model? Does eGFR remain a predictor in this case? Given the advanced age of these patients, are there any data on dementia which is also a risk factor?

4. “The crude mortality rate 176 was almost tenfold in CKD patients with COVID-19 (86/193, 44.6%)…” Again these were predominantly hospitalised patients however? I think it’s a bit misleading to call these “CKD patients” when they have so many co-morbidities. The authors here would be more accurate saying there was a 10x death rate in older, sicker, more multimorbid patients in the PRIP cohort who were hospitalised than those who were not hospitalised. This is a very different sentiment and statement.

5. The official figures from CPD will presumably include patients with CKD as well as young adults, (children even?) etc? If the authors wish to demonstrate that CKD is a risk factor for death the control group should be similarly elderly multimorbid patients with just as much additional disease, but without CKD. Otherwise, their finding is that “elderly multimorbid patients” have a higher infection rate (?or testing rate) + mortality than an averaged population including young healthy patients. Is the general population age matched? Or matched for other co-morbidities?

6. At the risk of repeating myself, The mortality is really high –I do worry there’s a bias here to just capturing the patients sick enough to end up in hospital and thus skewing the fatality rate which is really a “fatality rate of covid19 admissions in elderly CKD patients. These are really sick old people – 87% CV disease, 38% COPD, 10% Cancer, 35% diabetes. I don’t think its accurate to attribute this very high mortality to CKD based on these data.

Re: PRIP cohort

7. The study population is not well defined here. It is not clear to what extent the study population has captured ALL CKD in the region. This is important because the authors label these as CKD patients and everyone else as “non CKD” – are these in fact referrals based on rapid progression or higher risk CKD? What % of the population with CKD are not in the PIRP cohort? Does the PRIP cohort include children and young people, or transplants on immunosupression? The authors mention the cohort includes those under follow up by nephrology and GP, but what is the breakdown of CKD stage? Does COVID mortality vary accordingly?

8. Were the admissions to hospital for COVID-19, or where these unrelated admission with incidental tests? What was the proportion? Admitted patients will have had multiple tests, so there may be a detection bias here.

9. The 95% hospitalisation rate seems extremely high – There must presumably be a major bias here towards the hospitalised patients as there was no routine testing in the community of the PRIP cohort so asymptomatic cases and mild disease that didn’t present for a test won’t have been captured. The COVID+ patients who were hospitalised will have had a test, but the COVID+ patients in the community may not. Unless there was routine testing, I don’t think these data have captured the full extent of COVID19+ in this population so I don’t think the 95% hospitalisation rate is valid.

Minor:

Line 183 the CFR is different to the rate at the start of the paragraph?

CKD stages mentioned in the statistical analysis section of methods but not in the paper

I appreciate there are geographical and cultural differences in practice, but Im not sure its reasonable to call these “pre-dialysis” patients - they are very sick patients who would not be offered RRT in many healthcare settings – these patients would be on conservative care pathways typically.

Figure 2a

I don’t think this is useful information and its very confusing to read – why is the date of onset of disease relevant? Why resulting in different death rates? Why are these seemingly arbitrary dates chosen?

**********

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Reviewer #1: Yes: L.B. Hilbrands

Reviewer #2: Yes: Eoin Daniel O'Sullivan

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PLoS One. 2021 Jul 9;16(7):e0254525. doi: 10.1371/journal.pone.0254525.r002

Author response to Decision Letter 0


8 Jun 2021

Reviewer #1: This study describes the incidence and outcome of COVID-19 in a cohort of CKD patients as compared to the general population living in the same region. The main finding is that both the incidence of COVID-19 and the mortality rate were around 10 times higher in CKD patients. This corresponds with the data of the OpenSAFELY study, where CKD was found to be major risk factor for COVID-19 related mortality.

Comments:

1. The results are described separately for the three provinces included in the region. Although there are some differences between the provinces, I doubt whether this affects the analysis for the main study outcomes. There was no specific research question formulated related to differences between provinces. I therefore belief that this aspect gets too much attention in the manuscript. For the primary analyses it suffices to use the entire population. Subsequently, it can be checked whether the main conclusions would change when provinces are analysed separately.

We thank the reviewer for his suggestion. Indeed, the analyses by provinces took a great amount of space in the results without any background information provided in the Introduction. We have now added the rationale behind this analysis. In summary, this reflects our intention to highlight geographical differences in the incidence of COVID-19 that have occurred at a local level.

2. The conclusion that the incidence of COVID-19 was higher in CKD patients than in the general population might not be justified since there was no universal screening for COVID-19. It is imaginable that CKD patients have more severe symptoms of COVID-19 and that the diagnosis is more often made than in the general population in which there might be a higher proportion of ‘subclinical’ COVID-19 cases. This issue should be discussed in more detail.

We acknowledged the reviewer’s suggestion to remove from the paper the part on the comparison of the incidence of COVID-19 between CKD patients and the general population.

3. In Table A, the main diagnosis in CKD patients is ‘hypertensive nephropathy’. Probably this diagnosis was used for patients who had CKD and were hypertensive. However, since most kidney diseases are accompanied by hypertension, this diagnosis should be reserved for patients in whom no other kidney disease is present and kidney biopsy shows characteristic vascular lesions. In fact, it appears that the underlying cause of CKD was unknown in the majority of patients.

We agree with the reviewer that the “hypertensive nephropathy” category might be also related to patients with unknown nephropathy and hypertension. Thus, we removed this variable from the predictors used in the multivariable logistic regression model of COVID-19.

4. Table A should provide the distribution over CKD stages

We have now added information on CKD stages in the supplementary materials

5. In Table A, the abbreviation BPCO should be explained. (Should be COPD?)

We apologize for this mistake; indeed, it was COPD and we have now changed the acronym throughout the text.

6. From Table 1 it is clear that the incidence of COVID-19 is much higher in CKD patients than in the general population. It is confusing that on P8, L154 it is stated that the proportion of cases in the CKD population was lower than in the general population.

That sentence was indeed not very clear. As it was related to Fig. 2 which has now been removed, we also deleted that sentence.

7. In the section on mortality, the authors use the terms crude mortality rate and case fatality rate. They should explan in the difference, if any, or use the same term throughout the manuscript.

We used the term crude mortality rate when referring to CKD patients without COVID-19 disease, and the term case fatality rate when referring to CKD patients with COVID-19 disease. However, to avoid possible confusion, in the current version of the manuscript we have always used the term crude mortality rate.

8. While the CKD stage is an important predictor of mortality, this is not mentioned in the text on p11.

Thank you for pointing this out, we have now mentioned in text the relevance of CKD stage as predictor of mortality

9. On page 11, line 202 there is referral to Table 6. This should be Table 5.

We apologize for this mistake, that has been corrected.

Reviewer #2: Dr Gibertoni and colleagues present a descriptive study of COVID-19 infection in an Italian cohort, focusing on a subpopulation of patients with CKD and comparing disease incidence and mortality to the general population and to those within the cohort with a + COVID test to those without any test. These are interesting data and the linkage of multiple datasets is commendable. The section on excess mortality is the strongest, and is enlightening. However I am concerned that the comparator groups are inappropriate throughout and the high mortality rate and hospitalisations may be misattributed to CKD as a result, leading to incorrect conclusions have been drawn as a result. A number of the data presented seem to undermine the authors main point.

Major issues:

The biggest issue for me is that the comparisons being made between groups seem inappropriate.

Re: Incidence of COVID19

1. Its not ideal comparing these PRIP patients to the general population. These are clearly very elderly comorbid patients, whereas the general population will include healthy young people and potentially even children. A more appropriate comparison would be a sick elderly cohort without CKD. As a result the incidence data is of limited utility.

We agree with the reviewer that comparing the incidence of COVID-19 in PIRP patients to the general population is inappropriate. A cohort of elderly individuals without CKD to use as reference was not available. For this reason, also following rev. #1’s suggestion, we removed Table 1 and maintained only the general figure of incidence in the population, avoiding to highlight the comparison of incidences.

2. Were the PRIP cohort test routinely, or more frequently than the general population? Why? what was the rate of testing in each?

There is no screening program specifically addressed to the PIRP patients, thus we do not have information regarding their rate of testing. Supposedly, they are likely to have been tested more frequently because they are older, multi-morbid and more at risk of being symptomatic if infected.

Re Cause of Death

1. If the cause of death was covid-19 in only 37.5% of these cases, does this not undermine the authors main point- that these patients had excess death due to COVID19 infection? Is this not compounded by the fact that 25% didn’t even die during the admission with COVID19?

We apologize for our lack of clarity regarding this point. First of all, it should be kept in mind that a relevant proportion of these deaths occurred when the cause of death coding was not yet updated to include COVID-19 disease. Thus, we have inevitably to deal with inaccuracy on this issue. By highlighting that 76.2% died during their hospitalization for COVID-19, we meant that this was the minimum proportion of CKD patients who, with the greatest likelihood, died of/for COVID-19.

Re: Mortality attributed to CKD

1. The patients with covid-19 were older, had more advanced renal disease, higher rates of CV disease, higher rates of COPD (Table 2 ). It is thus hard to say that CKD was responsible for infection or death here. I also suspect there was non-diagnosed covid19 in the “without covid19 group”.

In Table 2 we only compared clinical characteristics of CKD patients with and without COVID-19, therefore we were not implying that CKD was the cause of the disease, because all these were CKD patients. We cannot rule out the presence of non-diagnosed COVID-19 in the without covid19 group, however, as it was previously pointed out, this should likely be a negligible proportion of patients, given their high-risk profile.

2.What’s the adjusted r2 for this model? The OR for CV and COPD are rather large – the OR for eGFR is per unit, but very close to 1. How much a difference did this really make? ( what did using CKD stages reveal instead?)

Please see the answer to point 3.

3. BMI, ethnicity, social deprivation, liver disease and HIV infection are known risk factors for death in COVID- are these data available and how do they interact with the model? Does eGFR remain a predictor in this case? Given the advanced age of these patients, are there any data on dementia which is also a risk factor?

We thank you for these suggestions and we think that he still refers to the predictive model of COVID-19 incidence described in Table 2. We have updated this model by adding BMI and dementia, and using CKD-EPI stages in place of eGFR. We did not include HIV (only 20 subjects among CKD patients were found HIV+, none of them with COVID-19), liver disease (only 1.0% of patients had liver disease), ethnicity (because only the Caucasian/Afro-american distinction was available) and social deprivation (data not available). We have also modified the identification of comorbidities. In the first version of the manuscript, we used the M-CDS algorithm which is based solely on drugs dispensations and, because of that, it overestimated the presence of COPD (as it includes also the dispensation of mucolytics and corticosteroid inhalers) and other comorbidities. We have now used the Elixhauser algorithm and searched for diagnoses in the HDR records of 2017-19.

Results indicate that renal function is still a risk factor, with stage 4 having OR=1.562. CV and COPD are still risk factors as well, however, the OR of CV has decreased and the OR of COPD has increased. Tumors have now become a significant risk factor. Dementia was not much frequent and displayed an increased yet non-significant risk of COVID-19. The pseudo-R2 of this model is 0.068, however it must be kept in mind that the pseudo-R2 values are considerably lower than those of the R2 used in linear regression, and that pseudo-R2 values as low as 0.2-0.4 indicate excellent model fit.

4. “The crude mortality rate 176 was almost tenfold in CKD patients with COVID-19 (86/193, 44.6%)…” Again these were predominantly hospitalised patients however? I think it’s a bit misleading to call these “CKD patients” when they have so many co-morbidities. The authors here would be more accurate saying there was a 10x death rate in older, sicker, more multimorbid patients in the PRIP cohort who were hospitalised than those who were not hospitalised. This is a very different sentiment and statement.

To address this and the following request by the reviewer we conducted an additional analysis based on all hospitalizations of January-July 2020 for COVID-19 disease. We then performed a multivariable logistic regression using mortality as the outcome to determine whether CKD patients in the PIRP cohort had a higher mortality risk than the rest of patients hospitalized for COVID-19, adjusting for age, sex, comorbidities and the province of residence. This model shows that PIRP patients had a 43.8% higher risk compared to non-PIRP patients.

As not all CKD patients participate in the PIRP project, we cannot rule out the possibility that other hospitalized were not identified as CKD. Keeping these limitations in mind, we think that this analysis may help elucidating the effect of CKD on COVID-19 related mortality.

5. The official figures from CPD will presumably include patients with CKD as well as young adults, (children even?) etc? If the authors wish to demonstrate that CKD is a risk factor for death the control group should be similarly elderly multimorbid patients with just as much additional disease, but without CKD. Otherwise, their finding is that “elderly multimorbid patients” have a higher infection rate (?or testing rate) + mortality than an averaged population including young healthy patients. Is the general population age matched? Or matched for other co-morbidities?

The reviewer is right in mentioning that the infection rate of CKD patients cannot be compared with that of the general population. We have now omitted this comparison from our results and reported the incidence in the general population at the beginning of the section “Incidence of COVID-19” only for descriptive purposes.

6. At the risk of repeating myself, The mortality is really high –I do worry there’s a bias here to just capturing the patients sick enough to end up in hospital and thus skewing the fatality rate which is really a “fatality rate of covid19 admissions in elderly CKD patients. These are really sick old people – 87% CV disease, 38% COPD, 10% Cancer, 35% diabetes. I don’t think its accurate to attribute this very high mortality to CKD based on these data.

We understand that the in-hospital mortality of CKD patients is high. It is actually higher than that reported for CKD patients enrolled in other registries (32.9%, LEOSS Study Group, 2021). We have now cited LEOSS study in which 97.1% of CKD patients with PCR- or rapid-test confirmed infection were hospitalized, a figure consistent with our report (95.4%).

As to the comorbidity, we have now used the standardized Elixhauser algorithm to identify comorbid conditions, as mentioned in the reply to point 3) and we found that the prevalence of comorbid conditions is lower.

Re: PRIP cohort

7. The study population is not well defined here. It is not clear to what extent the study population has captured ALL CKD in the region. This is important because the authors label these as CKD patients and everyone else as “non CKD” – are these in fact referrals based on rapid progression or higher risk CKD? What % of the population with CKD are not in the PIRP cohort? Does the PRIP cohort include children and young people, or transplants on immunosupression? The authors mention the cohort includes those under follow up by nephrology and GP, but what is the breakdown of CKD stage? Does COVID mortality vary accordingly?

We thank the reviewer for this suggestion. In the ‘Study population’ section we have now described the inclusion criteria in the project, clarified that CKD patients enrolled in PIRP do not include all patients with CKD in their area, and provided an estimate of the population with CKD living in the AUSL Romagna area that are followed up in PIRP.

In the Supplementary materials, we have now added Table A in which patients characteristics are compared by CKD-EPI stage at the last visit before COVID-19 infection. This table shows that the majority of patients included in the study were in stages 3b (39.1%), 4 (28.4%) and 3a (21.5%).

The proportion of young patients (<50 yrs) in the PIRP cohort of AUSL Romagna is 4.17%, a low figure which stems from the inclusion criteria.

By including CKD stage in the regression of in-hospital mortality we showed that CKD stage 4 patients are at a higher risk of mortality. The survival curves and log-rank test provided in Supplementary materials already showed that mortality risk increased with increasing CKD stage.

8. Were the admissions to hospital for COVID-19, or where these unrelated admission with incidental tests? What was the proportion? Admitted patients will have had multiple tests, so there may be a detection bias here.

All patients that we reported as COVID+ because they were hospitalized had the COVID-19 diagnosis identified from a specific code in the hospital discharge records. We are not able to distinguish who was admitted already COVID+ from those who were infected during their hospital stay.

9. The 95% hospitalisation rate seems extremely high – There must presumably be a major bias here towards the hospitalised patients as there was no routine testing in the community of the PRIP cohort so asymptomatic cases and mild disease that didn’t present for a test won’t have been captured. The COVID+ patients who were hospitalised will have had a test, but the COVID+ patients in the community may not. Unless there was routine testing, I don’t think these data have captured the full extent of COVID19+ in this population so I don’t think the 95% hospitalisation rate is valid.

We understand that our data refer to the first wave of the pandemic, in which no routine tests were performed and only symptomatic patients were seen in the health care facilities. In particular, at that time, CKD patients with COVID-19 were very likely to be hospitalized because of their complex clinical conditions. However, as we explained in a previous reply, most of these patients are in a particularly vulnerable state, and all of them have a direct connection with hospital nephrologists, as they are followed-up in a prevention program. We then hypothesize that the proportion of not tested COVID-19+ patients among them should be quite low.

Minor:

Line 183 the CFR is different to the rate at the start of the paragraph?

The CFR that was reported at line 183 referred to a sub-analysis that we made with the aim to compare the CFR that we found in PIRP patients to that found in an Italian survey on patients on dialysis. To obtain comparable figures, we restricted the CFR computation to a smaller time frame, as specified in lines 180-181.

CKD stages mentioned in the statistical analysis section of methods but not in the paper

We have added CKD stages as requested

I appreciate there are geographical and cultural differences in practice, but Im not sure its reasonable to call these “pre-dialysis” patients - they are very sick patients who would not be offered RRT in many healthcare settings – these patients would be on conservative care pathways typically.

We have used this terminology to reflect our selection of CKD stage 1 to 5 patients. As we explained in the ‘Study population’ section, our patients participate in a prevention program whose specific aim is to delay their initiation of RRT. Thus, our cohort includes both very sick patients who are in the course of being prepared for RRT and patients with slower progression who are maintained in conservative care. To avoid the possibility of confusion we have now changed the definition in the title from ‘pre-dialysis’ to ‘non-dialysis’ patients

Figure 2a

I don’t think this is useful information and its very confusing to read – why is the date of onset of disease relevant? Why resulting in different death rates? Why are these seemingly arbitrary dates chosen?

The reason why we included the date of onset is that, in the initial phase of the pandemic, hospitals and healthcare systems were not prepared to treat the number of infected patients that showed up. Thus, patients with similar characteristics might have experienced different mortality because they were infected in the early phase rather in subsequent phases when healthcare system efficacy was higher. The timeframes were chosen according to the phases of the epidemic curve of COVID-19 in Italy, with shorter intervals during the high epidemic phase up to the beginning of May (when the strictest containment measures were enforced) and longer intervals afterwards. We have now specified in the ‘Statistical analysis’ section the rationale behind this.

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Decision Letter 1

Giuseppe Remuzzi

29 Jun 2021

COVID-19 incidence and mortality in non-dialysis chronic kidney disease patients

PONE-D-21-06894R1

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Acceptance letter

Giuseppe Remuzzi

1 Jul 2021

PONE-D-21-06894R1

COVID-19 incidence and mortality in non-dialysis chronic kidney disease patients

Dear Dr. Gibertoni:

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Associated Data

    This section collects any data citations, data availability statements, or supplementary materials included in this article.

    Supplementary Materials

    S1 Appendix. Supporting Information, including Tables A, B, C, D and E.

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    Data Availability Statement

    The datasets generated and/or analysed during the current study are property of a third party that is Emilia-Romagna Regional Health Agency (https://assr.regione.emilia-romagna.it/) and, although they are anonymized, datasets are not publicly available due to the current regulation on privacy. The description of the administrative databases is available from the website https://salute.regione.emilia-romagna.it/siseps/sanita/asa/documentazione. Other researchers can obtain access to the data through a formal request based on a research project to the Romagna Local Health Authority.


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