Enhancing detection of SARS-CoV-2 re-infections using longitudinal sero-monitoring: demonstration of a methodology in a cohort of people experiencing homelessness in Toronto, Canada

Table 2 – Comparison of serology and PCR/RAT evidence among participants with first or second re-infections identified through PCR or RAT testing (N = 31)

	Number (%)
Agreement
Serology=’Probable’ same or next interview	6 (19.3%)
Serology=’Possible’ same or next interview	7 (22.6%)
Serology=’Indeterminate’ same or next interview	9 (29.0%)
Missing data, cannot determine agreement
+PCR test < 14 days before final interview^a	4 (12.9%)
Self-reported + PCR test > 4 months before next interview^b	1 (3.2%)
Disagreement
Method unable to detect: both N values above linear range at both dilutions	1 (3.2%)
No evidence, no explanation	3 (9.7%)

^a These participants might have mounted antibodies by the subsequent interview but had no further interviews
^b This participant missed a few interviews and reported a positive PCR test early in this prolonged period. It is possible they mounted a response which cleared by the time serology was again available

ISSN: 1471-2334