Severe Acute Respiratory Syndrome Coronavirus-2 seroprevalence in South-Central Uganda, during 2019–2021

BMC Infectious Diseases

Table 1 SARS-CoV-2 seroprevalence estimates, adjusting for test performance

Category	IgM_only (CoronaCheck, then Architect)	IgM_and_IgG (CoronaCheck)	IgG_only (CoronaCheck)	Overall adjusted prevalence (95% CI)^e
HCW, (N = 753)
Crude number + ve^a	46	102	11	200.8/753 (26.7%, CI = 23.5–29.8)
Crude prevalence^b	6.1%	13.5%	1.5%
Adjusted prevalence^c	7.9%	16.3%	2.4%
Adjusted number + ve^d	59.7	122.9	18.2
Cohort participants, (N = 227)
Crude number + ve	7	15	5	35.4/227 (15.6%, CI = 10.9, 20.3)
Crude prevalence	3.1%	6.6%	2.2%
Adjusted prevalence	4.0%	8.0%	3.6%
Adjusted number + ve	9.1	18.1	8.3
Early samples, (N = 636)
Crude number + ve	8	1	2	14.9/636 (2.3%, CI = 1.2, 3.5)
Crude prevalence	1.3%	0.2%	0.3%
Adjusted prevalence	1.6%	0.2%	0.5%
Adjusted number + ve	10.4	1.2	3.3

^aCrude number + ve are the number of participants who tested positive on that test
^bCrude prevalence = crude number + ve/number of participants tested
^cAdjusted prevalence = (crude prevalence + specificity − 1)/(sensitivity + specificity − 1). The sensitivity and specificity of CoronaCheck is 81.1% and 100% respectively for IgM; 60.5% and 100% respectively for IgG; and 83.0% and 100% for IgM and IgG combined. Sensitivity and specificity of the Architect assay is 95.0% and 99.56% respectively for IgM. Combined sensitivity of CoronaCheck and the Architect assay when used serially for IgM = Se1 × Se2 = 81.1% × 95.0% = 77.0%; while the combined specificity of the two assays used serially = 1 − (1 − Sp1)*(1 − Sp2) = 1 − (1 − 100%) × (1–99.56%) = 100%
^dAdjusted number + ve = adjusted prevalence × number of participants tested
^eOverall adjusted prevalence = (Sum of adjusted numbers + ve on IgM only, IgM and IgG, and IgG only)/number of participants

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