An optimized stepwise algorithm combining rapid antigen and RT-qPCR for screening of COVID-19 patients.

BACKGROUND & AIM: We investigated the combination of rapid antigen detection (RAD) and RT-qPCR assays in a stepwise procedure to optimize the detection of COVID-19. METHODS: From August 2020 to November 2020, 43,399 patients were screened in our laboratory for COVID-19 diagnostic by RT-qPCR using nasopharyngeal swab. Overall, 4,691 of the 43,399 were found to be positive, and 200 were retrieved for RAD testing allowing comparison of diagnostic accuracy between RAD and RT-qPCR. Cycle threshold (Ct) and time from symptoms onset (TSO) were included as covariates. RESULTS: The overall sensitivity, specificity, PPV, NPV, LR-, and LR+ of RAD compared with RT-qPCR were 72% (95%CI 62%-81%), 99% (95% CI95%-100%), 99% (95%CI 93%-100%), and 78% (95%CI 70%-85%), 0.28 (95%CI 0.21-0.39), and 72 (95%CI 10-208) respectively. Sensitivity was higher for patients with Ct ≤ 25 regardless of TSO: TSO ≤ 4 days 92% (95%CI 75%-99%), TSO > 4 days 100% (95%CI 54%-100%), and asymptomatic 100% (95%CI 78-100%). Overall, combining RAD and RT-qPCR would allow reducing from only 4% the number of RT-qPCR needed. CONCLUSIONS: This study highlights the risk of misdiagnosing COVID-19 in 28% of patients if RAD is used alone. A stepwise analysis that combines RAD and RT-qPCR would be an efficient screening procedure for COVID-19 detection and may facilitate the control of the outbreak.

The effects that well depth and wellhead protection have on bacterial contamination of private water wells in the Estes Park Valley, Colorado.

Over the past five years, it is estimated that 10% of residential water wells have tested positive for total coliform and 2% for E.coli bacteria in the Estes Park Valley, Colorado. Many of these water wells are shallow or hand-dug in construction. In this study, samplings of 30 private untreated water wells were tested for total coliform bacteria in the Estes Park Valley. Water wells were classified into three categories for well depth (<99 feet [30.2 m], 100-199 feet [30.5-60.7 m], and >200 feet [61 m]) and for wellhead protection (poor, fair, and good). Results indicated that 71% of the wells less than 199 feet (60.7 m) tested positive for total coliform (chi2 = 15.559, p < .0001). Also, 71% of wells classified as having poor and fair wellhead protection tested positive for total coliform (chi2 = 13.084, p = .001). This study determined that wellhead protection and well depth does play a role in bacterial contamination of water wells.