Repeated antigen testing among severe acute respiratory coronavirus virus 2 (SARS-CoV-2)-positive nursing home residents

Abstract

Repeated antigen testing of 12 severe acute respiratory coronavirus virus 2 (SARS-CoV-2)-positive nursing home residents using Abbott BinaxNOW identified 9 of 9 (100%) culture-positive specimens up to 6 days after initial positive test. Antigen positivity lasted 2-24 days. Antigen positivity might last beyond the infectious period, but it was reliable in residents with evidence of early infection.

Fig. 1.

Timeline of BinaxNOW antigen testing at a nursing home experiencing an outbreak of SARS-CoV-2 infections. The facility conducted antigen testing of residents using BinaxNOW from October 7 through October 21, 2020. From October 22, 2020, through November 3, 2020, the CDC conducted 3 facility-wide point-prevalence surveys (PPSs) among 127 residents using BinaxNOW (results published in McKay et al). Day 0 denotes the dates participants of the longitudinal evaluation were first identified as antigen positive during a PPS. Specimen collection for the longitudinal evaluation began 1–3 days after Day 0.

Fig. 2.

SARS-CoV-2 antigen, RT-PCR, and virus culture results from 12 nursing home residents participating in a longitudinal evaluation to characterize Abbott BinaxNOW COVID-19 Ag Cards. Specimens collected on days −15 through −1 were tested by the facility. Day 0 is the day participants first tested positive during a point-prevalence survey (PPS) conducted by the CDC. Specimens collected on days 1–9 were for the longitudinal evaluation. Cycle threshold (Ct) values were rounded to the nearest whole value; specimens with Ct values <40 were considered positive.