the staff of the Ridgewood blog
Ridgewood NJ, according to the Johns Hopkins Center for Health Security in December 2020, the US CDC updated its COVID-19 quarantine guidance to offer several options that allow individuals to shorten their 14-day quarantine period following a known exposure to SARS-CoV-2. Specifically, individuals who are unable to quarantine for the full 14 days can end their quarantine after 10 days if they exhibit no symptoms or after 7 days if they test negative on Day 5 or later. The CDC’s MMWR published 2 recent studies that provide analysis of the transmission risk associated with shorter quarantine periods.
The first study was conducted by the US CDC COVID-19 Response Team and the COVID-19 Collegiate Athlete Testing Group, in collaboration with researchers from several US universities. The researchers evaluated SARS-CoV-2 testing data for 1,830 US college athletes who were quarantined and tested after exposure to known COVID-19 cases. Among these athletes, 458 (25%) tested positive at some point during their quarantine period, including 137 who never reported COVID-19 symptoms. Among 620 athletes with positive tests*, 303 (48.9%) had positive tests by Day 2 of quarantine and 453 (73.1%) by Day 5. For those who had a negative test on Day 5, the researchers estimate the risk of testing positive after that point to be 26.9%, including 14.2% after Day 7 and 4.7% after Day 10. Notably, however, 26 of the 29 athletes that tested positive on Days 11-14 were not tested at all prior to that point, so it is possible that they would have tested positive on earlier tests, had they been conducted.
*Including additional data from schools that only reported positive tests.
Officials from the Vermont (US) Department of Health issued recommendations for a shorter quarantine period in May 2020, 7 months before the US CDC update. The Vermont policy stated that individuals could conclude their quarantine period if they tested negative on or after Day 7, based on data indicating that approximately 75% of COVID-19 patients developed symptoms within 7 days of exposure. The researchers analyzed test results for 2,200 contacts of known COVID-19 cases who were tested on Days 7-10 after exposure, collected in May-November 2020. In total, 87 (4%) of these individuals tested positive on Days 7-10, including 24 (25%) who were asymptomatic at the time of testing. The researchers also present data on the results for subsequent testing for a subset of these individuals. Among those who initially tested negative, 262 were tested again within 7 days—154 initially tested on Day 7 and 108 initially tested on Days 8-10. None of those individuals tested positive on the second test, providing evidence that there is relatively low risk of becoming infectious after a negative test later in the quarantine period. This study included data from a small proportion of individuals who ended their quarantine early, but it does provide some evidence that the risk of becoming infectious late in the quarantine period is relatively low.