February 3, 2021

Transmission of COVID-19 in 282 Clusters in Catalonia, Spain: A Cohort Study

Category: Article Summary

Topic: Transmission

Keywords (Tags): transmission

The risk of transmission of COVID-19 was greater when the index case had a higher concentration of virus. A cohort study of 282 COVID-19 clusters (n=314 patients) in Spain conducted from March-April 2020 indicated that the risk of symptomatic COVID-19 was associated with the viral load of the index case. The secondary attack rate ranged from 12% when the index case had a lower viral load (< 1 × 10⁶ copies per mL) to 24% with a higher load (>1 × 10¹⁰ copies per mL) (aOR=1.3 per log₁₀ increase in viral load). Increased risk of transmission was also associated with household contact with an infected person (aOR=3.0) and older age of the contact (aOR=1.02 per year). Time to onset of symptomatic COVID-19 also decreased with increased viral load, from a median of 7 days (IQR 5–10) for individuals with lower initial viral load to 5 days for those with a higher initial load.

Marks et al. (Feb 3, 2021). Transmission of COVID-19 in 282 Clusters in Catalonia, Spain: A Cohort Study. The Lancet Infectious Diseases. https://www.thelancet.com/journals/laninf/article/PIIS1473-3099(20)30985-3/fulltext