A key question that has remained largely unanswered is the extent and duration of antibody response in asymptomatic patients. that antibody response in asymptomatic patients is categorically different than in symptomatic hospitalized patients with COVID-19. values using Crawford and Howells adjusted test.5 Additionally, percentage of OD change was defined as (Sample OD C mean [negative control ODs])/(positive control OD ? mean [negative control ODs]) 100%. A sample was considered positive if two criteria were satisfied: (a) the sample OD was significantly greater than the mean of negative controls at the 0.001 level and (b) the percentage of OD change was above 10%. N protein and RBD data were analyzed separately, and Acumapimod a test was considered positive as long as one of the antigens was MTC1 positive. To evaluate the sensitivity and specificity of the assay, we also collected and analyzed 76 pre-COVID-19 donors as independent negative controls and 11 samples from hospitalized patients with confirmed SARS-CoV-2 infection as positive controls. Using a value threshold of 0.001 and a 10% percentage cutoff, the specificities for N protein (1:500 dilution) and RBD (1:250 dilution) were 97.36% and 96.05%, respectively. The sensitivities for N protein and RBD were both 100%. We used descriptive statistics including mean, standard deviation, frequency, and percentage to describe the study population. Body mass index and number of hours worked in high-risk units were first explored using histogram and boxplot. Their Acumapimod normality was then checked utilizing Q-Q plot and Shapiro-Wilk test. The results suggested no significant departures from the normal distribution for both variables. Thus, we used Students test to compare the study groups with regard to body mass index and length of time working in the high-risk units during the past week. Categorical variables were compared between antibody-positive and -negative individuals using chi-square test and Fisher exact test depending on which was more appropriate. We used Students paired test to assess the temporal changes in OD values. Additionally, we drew 10,000 samples to obtain the bootstrap estimate of the standard error of the mean difference. We found the bias to be negligible for both antigens. Furthermore, we confirmed the results of the paired test with that of Wilcoxon signed-rank test. All statistical analysis was performed using SAS statistical software 9.4, and the significance level was considered 0.05 throughout the analysis. RESULTS Of the 197 study participants, 165 (83%) were white and 148 (75%) were women value= 0.20), while the decrease in the mean OD of the RBD antigen was statistically significant ( 0.0006) em (Figure 3) /em . Two subjects tested negative at week 1 but positive at week 3. There was no statistically significant difference in baseline characteristics or exposure status between patients with detectable IgG antibodies to SARS-CoV-2 vs those with no detectable IgG antibodies em (Table 1 /em ). Open in a separate window Figure 3. A plot Acumapimod of patients who had detectable IgG antibody (plotted according to either N or RBD IgG positivity) at two different time points. Most patients had a weak positive signal to begin with, which decreased or was lost at testing 2 weeks later. DISCUSSION The 4.2% prevalence of RT-PCRCpositive subjects was lower than expected in our asymptomatic but high-risk group of HCWs. In addition, the fact that no positive results occurred after the first week of testing was also unexpected considering the significant amount of reported exposure our subjects had to COVID-19 patients during our study enrollment time em (Figure 4) /em . Our results were similar to those of Treibel et?al.6 They reported only a slightly higher rate of PCR positivity at 7.1% Acumapimod and a nearly sixfold drop in PCR-positive detection in subsequent serial testing in HCWs at a London hospital.6 These findings could be a result of efficacy of appropriate infection control measures and protective equipment donning in our subjects. Of note, our institution had implemented strict personal protective products.