SARS-CoV-2 transmission among high-risk contacts

| 3 November 2020 | Singapore’s comprehensive approach to COVID-19 control, much of which was prepared following the 2003 SARS epidemic, is likely to have contributed to the low secondary attack rate among household and non-household contacts during the study period.

Ng OT, Marimuthu K, Koh V, et al. SARS-CoV-2 seroprevalence and transmission risk factors among high-risk close contacts: a retrospective cohort study. Lancet Infect Dis 2020, published 2 November. Full-text:

Excellent retrospective cohort study by Vernon Lee, Oon Tek Ng and colleagues Between Jan 23 and April 3, 2020, the authors identified 7,518 close contacts (1779 [23%] household contacts, 2231 [30%] work contacts, and 3508 [47%] social contacts) linked to 1114 PCR-confirmed index cases.

The secondary clinical attack rate:

Household contacts: 5.9% (95% CI 4.9–7.1).

Particular risk factors:

  1. Sharing a bedroom (multivariable odds ratio [OR] 5.38)
  2. Being spoken to by an index case for 30 min or longer (7.86)

Non-household contact: Work contacts, 1.3% (0.9–1.9); social contacts, 1.3% (1.0–1.7).

Particular risk factors:

  1. Exposure to more than one case (3.92)
  2. Being spoken to by an index case for 30 min or longer (2.67)
  3. Sharing a vehicle with an index case (3.07).

Among both household and non-household contacts, indirect contact, meal sharing, and lavatory co-usage were not independently associated with SARS-CoV-2 transmission.

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