To the Editor
Spain is one of the countries most affected by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic. There were nearly two million confirmed cases and more than 50 000 deaths by December 2020 [1]. A recent national serological surveillance study carried out in our country detected an overall 5% seroprevalence in the general population, with important geographical variability that ranged from 3% to 10% [2].
Health-care workers (HCW) have an increased risk of exposure to SARS-CoV-2. Household contacts and the socialization between HCW could also give exposure to infection.
Our objective was to analyse the impact of the first peak of the coronavirus disease 2019 (COVID-19) pandemic in HCW from a tertiary teaching hospital in Madrid (Spain), as well as evaluate a lateral flow inmunoassay (LFIA) for applicability to seroprevalence studies. The study was carried out in May–June 2020, during the slowdown phase of the epidemic wave. To avoid selection bias, serology testing was offered to all staff working in the hospital (6747 HCW). Testing was performed by a LFIA (Hangzhou ALLTEST Biotech Co. Ltd, Hangzhou, China) in whole blood for fast identification of IgG and IgM antibodies against SARS-CoV-2, and secondly serum samples were tested by Vircell COVID-19 ELISA IgG and IgM/IgA test (Vircell Spain S.L.U., Granada, Spain). Ethical approval was obtained from the Hospital Ethics Committee of Clinical Research (Ref 249/20) with a waiver of informed consent. Those participants with a positive IgM result were tested with an SARS-CoV-2 RT-PCR (TaqMan 2019-nCoV Assay kit v1. ThermoFisher Scientific, Inc. Waltham, MA, USA). In this group, a second serum sample was obtained 2 weeks after the first one for IgG seroconversion analysis.
Overall, 5875/6753 HCW (87.0%) participated in the study (4718/5875 women (80.3%) and 1157/5875 men (19.7%)). IgG antibodies were detected in 1363/5875 (23.1%, 95% CI 22.1%–24.3%), being significantly more prevalent in men (25.5%, 95% CI 23.4%–27.8%; p 0.01) than in women (22.3%, 95% CI 21.1%–22.3%). The most affected HCW were Department Heads and Nursing Supervisors (30.0%, 95% CI 23.2%–37.5%), probably because of the high number of management meetings in the first weeks of the epidemic wave, followed by hospital porters (26.8%, 95% CI 22.5%–31.5%), residents (25.7%, 95% CI 21.6%–30.1%), nursing staff (24.2%, 95% CI 22.0%–26.5%) and physicians (23.7%, 95% CI 21.0%–26.7%) (Table 1 ).
Table 1.
Prevalence of IgG performed with ELISA (Vircell COVID-19 ELISA IgG test) by sex, professional categories and Departments
| n (%) | Prevalence IgG % (95% CI) | p value | |
|---|---|---|---|
| Total | 5875 | 23.2 (22.1–24.3) | |
| Sex | 0.01 | ||
| Women | 4324 (80.3) | 22.3 (21.1–23.6) | |
| Men | 1155 (19.7) | 25.5 (23.4–27.8) | |
| Macrocovid | 0.007 | ||
| Yes (first line) | 1920 (32.6) | 24.8 (22.9–26.8) | |
| Yes (second line) | 1235 (21.1) | 24.8 (22.4–27.3) | |
| No | 2720 (46.3) | 21.3 (19.8–22.9) | |
| Professional category | 0.000 | ||
| Nursing staff | 2476 (42.1) | 24.2 (22.0–26.5) | |
| Physician | 897 (15.3) | 23.7 (21.0–26.7) | |
| Resident | 428 (7.3) | 25.7 (21.6–30.1) | |
| Hospital porter | 388 (6.6) | 26.8 (22.5–31.5) | |
| Researcher | 296 (5.0) | 24.0 (19.2–29.3) | |
| Technician | 334 (5.7) | 20.1 (15.9–24.8) | |
| Executive | 14 (0.2) | 14.3 (1.8–42.8) | |
| Department Head/Nursing Supervisor | 170 (2.9) | 30.0 (23.2–37.5) | |
| Administrative | 481 (8.2) | 13.7 (10.8–17.1) | |
| Other (non-health services) | 391 (6.7) | 20.7 (16.8–25.1) | |
| Department | |||
| Allergy | 36 (0.6) | 22.2 (10.1–39.2) | |
| Anaesthesiology | 117 (2.0) | 13.7 (8.0–21.3) | |
| Cardiology | 106 (1.8) | 23.6 (15.9–32.8) | |
| Surgery | 776 (13.2) | 24.2 (21.3–27.4) | |
| Dermatology | 35 (0.6) | 17.1 (6.6–33.6) | |
| Endocrinology | 82 (1.4) | 29.3 (19.7–40.4) | |
| Pharmacy | 88 (1.5) | 11.4 (5.6–19.9) | |
| Physiotherapy | 38 (0.7) | 26.3 (13.4–43.1) | |
| Gastroenterology | 91 (1.6) | 29.7 (20.5–40.2) | |
| Geriatric | 21 (0.4) | 33.3 (14.6–57.0) | |
| Gynaecology | 66 (1.1) | 18.2 (9.8–29.6) | |
| Haematology | 91 (1.6) | 12.1 (6.2–20.6) | |
| Infectious Disease | 117 (2.0) | 28.2 (20.3–37.3) | |
| Laboratory | 359 (6.1) | 17.5 (13.8–21.9) | |
| Preventive medicine | 22 (0.4) | 9.1 (1.1–29.2) | |
| Administration/Services | 1070 (18.2) | 21.3 (18.9–23.9) | |
| Internal medicine | 187 (3.2) | 34.2 (27.5–41.5) | |
| Nephrology | 111 (1.9) | 10.8 (5.7–18.1) | |
| Pulmonology | 72 (1.2) | 38.9 (27.6–51.1) | |
| Neurophysiology | 26 (0.4) | 19.2 (6.6–39.4) | |
| Neurology | 88 (1.5) | 27.3 (18.3–37.8) | |
| Ophthalmology | 86 (1.5) | 17.4 (10.1–27.1) | |
| Oncology | 126 (2.1) | 29.4 (21.6–38.1) | |
| Otorhinolaryngology | 40 (0.7) | 5.0 (0.6–16.9) | |
| Paediatric | 89 (1.5) | 24.7 (16.2–35.0) | |
| Psychiatry | 73 (1.2) | 31.5 (21.1–43.4) | |
| Radiology | 287 (4.9) | 25.1 (20.2–30.5) | |
| Rehabilitation | 31 (0.5) | 19.4 (7.5–37.5) | |
| Rheumatology | 35 (0.6) | 31.4 (16.9–49.3) | |
| Occupational Health and Safety Service | 14 (0.2) | 64.3 (35.1–87.2) | |
| Traumatology | 63 (1.1) | 36.5 (24.7–49.6) | |
| Intensive care unit | 194 (3.3) | 17.5 (12.5–23.6) | |
| Emergency | 301 (5.1) | 31.9 (26.7–37.5) | |
| Urology | 82 (1.4) | 24.4 (15.6–35.1) | |
Prevalence among non-sanitary professionals was 16.8% (95% CI 13.7%–20.7%). First-line specialties, such as pneumology, internal medicine, geriatrics, emergencies or infectious diseases, showed a prevalence of nearly 30%, but also second-line specialties, such as traumatology (36.5%), psychiatry (31.5%) or rheumatology (31.4%). On the other hand, prevalence was significantly lower (13.7% and 17.5%, respectively) in highly-exposed staff from anesthesiology and intensive care units, which could be related to a higher perception of the risk and to extreme pre-emptive measures in their daily work.
Interestingly, 11.5% of IgG-positive HCW did not have any history of PCR testing, which could correspond to undiagnosed infections. Conversely, IgG was not detected in 6.1% of 411 HCW without a history of previous positive PCR result. Considering only HCW with positive IgM together with positive PCR post-serology and those with positive seroconversion, we demonstrated current asymptomatic infections in 1.1% of HCW.
Using ELISA as the reference technique, the global agreement between both tests for IgG was 96.9% (κ index = 0.9) (sensitivity 93.5%, 95% CI 92.1%–94.8% and specificity 98.0%, 95% CI 97.6%–98.4%). Global agreement for IgM was 86.9% (κ index = 0.4), with a specificity of 98.2% (95% CI 978%–98.5%) but the sensitivity was extremely low 33.1% (95% CI 30.2%–36.1%), which made it unreliable for diagnosis of acute or asymptomatic cases.
Our results contrast with lower prevalences in HCW from other countries. Local variations in hospital settings had been reported but always in agreement with community incidence, also in contrast to our findings [3]. Community acquisition as well as transmission between staff members cannot be ruled out as shown by the high prevalence found in non-health professionals (20.7%). The higher prevalence found in men than women is also relevant, particularly considering that two-thirds of the HCWs of our institution are women. This difference in sex prevalence was not found in the national serosurvey [2]. We detected 1.1% of asymptomatic infections, which is relevant considering that the study was carried out when the positivity rate in our hospital was under 1% and infections in the community were in the base of the epidemic curve. Seroprevalence studies are crucial for assessing the impact of the pandemic and for evaluating control measures. The use of a rapid test, such as LFIA, could be a suitable tool for this purpose. Our results demonstrate a good agreement between LFIA and the reference technique for IgG detection.
In conclusion, infections in HCW could increase the worsening of the pandemic by collapsing health services. HCW could contribute as a source of transmission to other co-workers, patients and their own relatives and households.
Transparency declaration
The authors declare that they have no conflicts of interest.
Funding
The study was performed with the hospital's own resources.
Acknowledgements
We want to thank Laura del Campo Albendea for help with statistical analysis, Laura Martinez-García, Melanie Abreu and Magdalena Muedra for helping to carry out the study and data collection. Also to Mary Harper for English revision of the manuscript. We are deeply grateful to all laboratory technicians, administrative personnel and nurses who made this seroprevalence study possible.
Editor: L. Leibovici
References
- 1.2020. https://www.mscbs.gob.es/en/profesionales/saludPublica/ccayes/alertasActual/nCov-China/situacionActual.htm [Accessed 1 December 2020]
- 2.Pollán M., Pérez-Gómez B., Pastor-Barriuso R., Oteo J., Hernán M.A., Pérez-Olmeda M. Prevalence of SARS-CoV-2 in Spain (ENE-COVID): a nationwide, population-based seroepidemiological study. Lancet. 2020;S0140–6736:31483–31485. doi: 10.1016/S0140-6736(20)31483-5. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 3.Self W.H., Tenforde M.W., Stubblefield W.B., Feldstein L.R., Steingrub J.S., Shapiro N.I. Seroprevalence of SARS-CoV-2 among frontline health care personnel in a multistate hospital network—13 academic medical centers, April–June 2020. MMWR Morb Mortal Wkly Rep. 2020;69:1221. doi: 10.15585/mmwr.mm6935e2. [DOI] [PMC free article] [PubMed] [Google Scholar]