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180: Characteristics of Persons With Positive COVID-19 PCR Tests Later Testing Negative for Antibodies

INTRODUCTION: The accuracy and value of SARS CoV-2 antibody (Ab) testing has been controversial Explanations for negative follow-up Ab tests (Ab-) in PCR+ persons could be poor assays/techniques or entirely absent, transient or delayed COVID-19 Ab responses However, prior corona virus experiences have paradoxically indicated Ab- testing among younger persons and those with milder illness The purpose here was to evaluate if age or illness severity correlate with Ab- assays in persons with prior COVID-19 PCR+ tests METHODS: Part of an on-going study, 2 dissimilar EMS agencies (fire-based vs 3rd service) in 2 far-distanced U S cities with contrasting populations, both evaluated prior PCR+ employees with IgM/IgG testing, but each used 2 different lateral flow chromatographic immunoassay (LFCIA) products Among 70 volunteers at Site 1, 39 were a reference group (RG) from the general population with no prior COVID-19 symptoms or testing (Sx-/NoPCR group) The other 48 (PCR+) principals at both sites had prior nasal swab PCR+ tests At a later date (2-8 weeks), the 48 received IgM/IgG fingerstick LFCIA testing and were surveyed (both sites) for pre-selected Sx categories, illness severity indicators, age, sex and date of PCR+ test RESULTS: Despite distinct differences in local demographics, agencies and assay products, findings were strikingly similar at both sites Of 48 prior PCR+ subjects, roughly 30% at either site (n=15/48;31 2%) were IgM-/IgG- (32 2% at site 1;29 4% at site 2) The mean age for the Sx-/NoPCR RG (n=39, all testing Ab-) was 45 51 yrs, range (R) 26-75 and similarly 43 97 (R=21- 81) for 33 PCR+/Ab+ subjects (p=NS) However, for those with prior PCR+ tests but Ab-, the mean age was 33 9 yrs (R=21-50);2-tailed p=0 009 vs PCR+/Ab+ and 0 003 vs RG Differences were near-identical within each site: Site 1 = 44 7 yrs, R=21-81 vs 34 7 R=21-50 (p=0 048;0 021 vs RG);Site 2: 42 75, R 25-62 vs 32 2, R=27-39 (p=0 048;0 003 vs RG) At both sites, trends were evolving for Ab- in milder disease, women and shorter PCR to Ab testing intervals CONCLUSIONS: Using different IgM/IgG LFCIA products in two highly-contrasted settings, 30% of persons with prior COVID-19 PCR+ tests were Ab- at both sites and, in either venue, those PCR+/Ab- persons were significantly younger than PCR+/Ab+ counterparts