Rates of recurrent positive SARS-CoV-2 swab results among patients attending primary care in Qatar

Dear Editor,

We read with interest the work of COCOREC (Collaborative study COvid RECurrences) study group.¹ Recurrent positive rt-PCR results for SARS-CoV-2 infection were reported from early in the epidemic.1, 2, 3, 4, 5, 6, 7, 8 Viral genomic sequences provided concrete evidence for reinfection by distinct SARS-CoV-2 infection.9, 10, 11, 12 The number of days in between both infections in viral genomic proven reports ranged from 48 to 142 days.

While viral genomic sequencing provides robust evidence, it does not lend itself well to everyday practice. The COCOREC study identified 11 cases of reinfection using well-defined criteria.¹ The group suggested recurrent positive rt-PCR results of more than 21 days following the resolution of symptoms as criteria for reinfection. The criteria though less specific, are more feasible to use in primary health care settings.

Utilising the criteria set by the COCOREC study group, this record-based study reports on the cases with recurrent positive RT-PCR nasopharyngeal swab for SARS-CoV-2 results in primary health care corporation (PHCC) settings in Qatar. PHCC is the largest primary care provider in Qatar with 27 health centers covering all the country. The organisational employs an electronic medical record (EMR), which links all public primary health care centers. For this study, all electronic data were extracted from the primary healthcare setting visits, and no sampling was needed.

The study population included patients attending with documented SARS-CoV-2 rt-PCR results during the study period. The study period was from February 10th, 2020, to July 30th, 2020, a total of 171 days. The recurrent positive population included all patients with a minimum number of 2 positive swabs and a minimum number of 21 days in between positive swab results. Inconclusive and reactive rt-PCR results were considered negative. During the study period, patients were entitled to a repeat swab if they are attending with new symptoms following the resolution of initial symptoms. A maximum number of days in between any positive swab results was calculated for those who met our definition criteria.

The study aims to answer the following questions. What is the maximum number of days in between positive swab results? What are the rates of recurrent rt-PCR SARS-CoV-2 positive results of more than 21 days, and what are the population characteristics?

Overview

During the study period, we retrieved a total of 63,444 patient records with 76,742 swab results. Only 62 patients met our inclusion criteria (62/63,444;0.1%).

The population was predominantly young. The mean age is 37.3 ± 12.2. (Median: 35 [Min: 11-Max: 74]). Male patients were more represented in the sample (49/62;70.6%). 2 female patients were pregnant (2/13; 15%). The percentage of current smokers was high (8/40;20%) (Table 1 ).

Table 1.

Characteristics of the population with recurrent positive results.

	Overall (N = 62)
Number of days between positive results
Mean (SD)	29.2 (11.6)
Range	21.0 - 84.0
Age
Mean (SD)	37.3 (12.2)
Range	11.0 - 74.0
Gender
Female	13 (21.0%)
Male	49 (79.0%)
HTN
No	54 (87.1%)
Yes	8 (12.9%)
DM
No	50 (80.6%)
Yes	12 (19.4%)
Asthma
No	55 (88.7%)
Yes	7 (11.3%)
COPD
No	62 (100.0%)
CVD
No	62 (100.0%)
CKD
No	62 (100.0%)
Dyslipidemia
No	51 (82.3%)
Yes	11 (17.7%)
Smoking Status
N-Miss	22
Never Smoker	29 (72.5%)
Former Smoker	3 (7.5%)
Current Smoker	8 (20.0%)
Pregnancy
N-Miss	49
Not Pregnant	11 (84.6%)
Pregnant	2 (15.4%)

The maximum number of days and rates of recurrent positives among the study population

84 days was the maximum number of days for recurrent positive and the mean of the maximum number of days between recurrent positive results is 29.2 ± 11.6. (Median: 25 [Min: 21-Max: 84]).

The rates for recurrent positive results are reported for the total recurrent positive (62) and the total study population, (63,444). The recurrent positive results of more than 42 days were rare (7/63,444,0.01%) (table 2 ).

Table 2.

 

Number of Days between recurrent positive	Counts	% of recurrent positive (62)	% of the total swabs (63,444)
21–30 Days	41	66.1 %	0.07%
30–42 Days	14	22.6 %	0.02%
>42 Days	7	11.3 %	0.01%

Summary

Recurrent positive findings could occur in all age groups and different population types, including paediatric, elderly, and pregnant patients. Current smoking status was highly prevalent among patients with recurrent positive results.

No previous studies reported to the rates of recurrent positive rt-PCR for SARS-CoV-2 infections. Given the extensive reporting of the SARS-CoV-2 infections, the number of case reports of recurrent positive and reinfection to date is extremely low, which agrees with our findings. Earlier studies reported that viral shedding is dynamic and continue in most cases 20–22 days but positive results were generally rare beyond 30 days. ¹³ So, one could theorise that recurrent positive results in symptomatic patients should be considered reinfection, especially if more than 42 days.

The rare occurrences of recurrent infections are reassuring to the world given the current surge and in favour of immunity. However, it does not allude to the length of that immunity. Given the rarity of recurrent positive results which is supported by our findings, vaccination should be recommended for patients with no earlier SARS-CoV-2 infection.

Strengths and limitations

The study utilised centralised database records that allowed for large sample size, 63,444 and long study period of 6 months. However, the record-based study does not report on the severity or the resolution of symptoms or the patients’ outcomes.

Informed consent

Data request and analysis were anonymous, and no patient consent was required.

Ethics statement

Anonymous data request approved by the department of clinical research, primary health care corporation with reference number PHCC/DCR/2020/04/031.