Seven-day COVID-19 quarantine may be too short: assessing post-quarantine transmission risk in four university cohorts

BackgroundDespite rising rates of vaccination, quarantine remains critical to control SARS-CoV-2 transmission. COVID-19 quarantine length around the world varies in part due to the limited amount of empirical data. ObjectiveTo assess post-quarantine transmission risk for various quarantine lengths. DesignCohort study. SettingFour US universities, September 2020 to February 2021. Participants3,641 students and staff were identified as close contacts to SARS-CoV-2-positive individuals. They entered strict or non-strict quarantine and were tested on average twice per week for SARS-CoV-2. Strict quarantine included designated housing with a private room, private bathroom and meal delivery. Non-strict quarantine potentially included interactions with household members. MeasurementsDates of exposure and last negative and first positive tests during quarantine. ResultsOf the 418 quarantined individuals who eventually converted to positive, 11%, 4.2%, and 1.2% were negative and asymptomatic on days 7, 10 and 14, respectively. The US CDC recently shortened its quarantine guidance from 14 to 7 days based on estimates of 2.3-8.6% post-quarantine transmission risk at day 7, significantly below the 11% risk we report here. Notably, 6% of individuals tested positive after day 7 in strict quarantine, versus 14% in non-strict quarantine. Ongoing exposure during quarantine likely explains the higher rate of COVID-19 in non-strict quarantine. LimitationsQuarantine should be longer for individuals using antigen testing, given antigen testings lower sensitivity than qPCR. Results apply in settings in which SAR-CoV-2 variants do not affect latent period. ConclusionsTo maintain the 5% transmission risk that the CDC used in its guidance, our data suggest that quarantine with qPCR testing 1 day before intended release should extend to 10 days for non-strict quarantine. Funding SourceNone.

Amplicon contamination in labs masquerades as COVID19 in surveillance tests

A cohort of laboratorians with positive SARS-CoV2 test results were uncovered during asymptomatic COVID-19 screening programs at six universities. Follow-up PCR and antibody tests showed that most of these cases were not true COVID-19 infection but instead arose from reverse-transcribed and amplified viral sequences (amplicons) that are generated during research. Environmental testing showed widespread contamination of amplicons in lab spaces including notebooks, keyboards, glasses, and doorknobs. Minimizing instances of amplicon contamination and developing protocols for handling suspected cases are critical to propel research efforts and to avoid diverting university and healthcare resources from patients with COVID-19. Removal of these individuals from the standard testing protocol, per CDC guidelines for positive cases, risks the spread of true infection. We discuss potential prevention and mitigation strategies.