Abstract
Background: We assessed the SARS-CoV-2 reinfection rate in a large patient cohort, and evaluated the effect of varying time intervals between two positive tests on assumed reinfection rates using viral load data. Methods: All positive SARS-CoV-2 samples collected between 1 March 2020 and 1 August 2021 from a laboratory in the region Kennemerland, the Netherlands, were included. The reinfection rate was analyzed using different time intervals between two positive tests varying between 2 and 16 weeks. SARS-CoV-2 PCR crossing point (Cp) values were used to estimate viral loads. Results: In total, 679,513 samples were analyzed, of which 53,366 tests (7.9%) were SARS-CoV-2 positive. The number of reinfections varied between 260 (0.52%) for an interval of 2 weeks, 89 (0.19%) for 4 weeks, 52 (0.11%) for 8 weeks, and 37 (0.09%) for a minimum interval of 16 weeks between positive tests. The median Cp-value (IQR) in the second positive samples decreased when a longer interval was chosen, but stabilized from week 8 onwards. Conclusions: Although the calculated reinfection prevalence was relatively low (0.11% for the 8-week time interval), choosing a different minimum interval between two positive tests resulted in major differences in reinfection rates. As reinfection Cp-values stabilized after 8 weeks, we hypothesize this interval to best reflect novel infection rather than persistent shedding.
Highlights
Since the start of the COVID-19 pandemic in early 2020, SARS-CoV-2 was first expected to induce a monophasic disease with at least transient immunity [1]
SARS-CoV-2 viral loads in respiratory samples lack comparability of Ct- or crossing point (Cp)-values derived from different laboratories, as these are assay- and method-specific [14]
It should be noted that most studies use different definitions of reinfection: though some choose a stringent definition including the requirement of a negative SARS-CoV-2 PCR result between two positive tests, reporting of COVID-19-related symptoms during both episodes, a minimal viral load, and evidence of genotypic variance between the two viral strains [7], others use only a selection of these [15]
Summary
Since the start of the COVID-19 pandemic in early 2020, SARS-CoV-2 was first expected to induce a monophasic disease with at least transient immunity [1]. The few larger cohort studies that assessed the incidence of reinfection with SARS-CoV-2 estimated a reinfection rate ranging from 0.10% to 0.26% during varying follow-up periods of 2–9 months [11–13]. The interpretation of these reports of SARS-CoV-2 reinfections is hampered by the methodological inconsistencies between studies. The major difference between studies, though, seems to be the chosen minimum time interval between two positive tests, which ranges from 8 to 82 days between studies [2,7], and which is likely to have a large influence on the reported prevalence of reinfection. We assessed the SARS-CoV-2 reinfection rate in a large patient cohort, and evaluated the effect of varying time intervals between two positive tests on assumed reinfection rates using viral load data. As reinfection Cp-values stabilized after 8 weeks, we hypothesize this interval to best reflect novel infection rather than persistent shedding
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