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

  1. Andrew Bo Liu
  2. Dan Davidi
  3. Hannah Emily Landsberg
  4. Maria Francesconi
  5. Judy T. Platt
  6. Giang T. Nguyen
  7. Sehyo Yune
  8. Anastasia Deckard
  9. Jamie Puglin
  10. Steven B. Haase
  11. Davidson H. Hamer
  12. Michael Springer
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Abstract

Background

Despite 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.

Objective

To assess post-quarantine transmission risk for various quarantine lengths.

Design

Cohort study.

Setting

Four US universities, September 2020 to February 2021.

Participants

3,641 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.

Measurements

Dates of exposure and last negative and first positive tests during quarantine.

Results

Of 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.

Limitations

Quarantine should be longer for individuals using antigen testing, given antigen testing’s lower sensitivity than qPCR. Results apply in settings in which SAR-CoV-2 variants do not affect latent period.

Conclusions

To 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 Source

None.

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