Strategies to determine the duration of isolation

At our 800-bed, tertiary-care, academic medical center in Baltimore, Maryland, hospitalized patients with a positive SARS-CoV-2 diagnostic test and no previous positive in the preceding 12 weeks are assigned a COVID-19 banner in the electronic health record (EHR), and they receive care using transmission-based precautions per CDC guidance. Prior to February 15, 2022, we used 2 strategies to determine the duration of these precautions: (1) a time-based strategy for asymptomatic or mild-to-moderate illness requiring at least 10 days from symptom onset (or diagnosis if asymptomatic), (2) a time and test (RT-PCR)–based strategy for critically ill and severely immunosuppressed patients (Supplementary Table online).

Beginning February 15, 2022, we implemented a SARS-CoV-2 antigen-test–based strategy to facilitate discontinuation of precautions using separate algorithms (Supplementary Fig. 1 online) for patients with (1) asymptomatic or mild-to-moderate disease, (2) critical illness, and (3) severe immunosuppression. Test eligibility was established by clinical improvement and ≥5 days from symptom onset for mild-to-moderate or critical illness and ≥14 days for severely immunosuppressed patients. For asymptomatic patients without a known COVID-19 exposure, antigen testing could begin immediately. Two consecutive negative tests ≥24 hours apart were required to discontinue precautions. The antigen-test–based strategy was ordered optionally at the discretion of clinical teams. Testing was performed using FDA-authorized point-of-care SARS-CoV-2 antigen test kits (CareStart COVID-19 Antigen) by trained registered nurses on weekdays only. Infection preventionists resolved the COVID-19 banner for patients meeting criteria for discontinuation of precautions. During this period, SARS-CoV-2 antigen testing was not utilized for any other indication in hospitalized patients.

Fig. 1.

Sequential point-of-care SARS-CoV-2 antigen test results during hospitalization with COVID-19.

Cohort selection

We included all patients aged ≥2 years with positive SARS-CoV-2 tests hospitalized from February 15 to September 1, 2022. During this time, all patients underwent routine SARS-CoV-2 PCR testing upon hospital admission, regardless of symptoms. Patients with duration of stay <48 hours and patients with COVID-19 banner present for <12 hours (ie, determined to be remote infection with residual PCR positivity based on history) were excluded.

Data collection

From the EHR, we obtained patient demographics, admission and discharge dates and times, location of care at admission, presence of COVID-19 symptoms, date and time of onset and resolution of the COVID-19 banner, and if performed, dates and times of antigen testing and test results.

Outcomes and analysis

We summarized patient characteristics for the overall cohort and separately for patients who underwent antigen testing and those who did not. For patients who underwent antigen testing, we calculated time from admission and time from COVID-19 banner onset to first antigen test, and the proportion of positive antigen test results for each sequential test performed. The primary outcome was duration of COVID-19 transmission-based precautions estimated using time from assignment of a COVID-19 banner to resolution. Bivariate analyses were conducted to compare patients who underwent antigen testing with those who did not and to compare patients who tested positive versus negative on initial antigen testing. We used the χ², Wilcoxon ranked-sum, or Student t test as appropriate. Data analysis was conducted using SAS version 9.4 software (SAS Institute, Cary, NC). This study was determined to be exempt from approval by the University of Maryland, Baltimore Institutional Review Board.