Covid-19 household transmission patterns

SARS-CoV-2 transmission electron microscope image.
SARS-CoV-2 as seen with a transmission electron microscope image. (By CDC/NIAID)

Four University of Florida researchers led a recent meta-analysis to uncover trends in household transmission of SARS-CoV-2, the virus that causes COVID-19. Their study published in mid-December in JAMA Network Open.

First author Zachary Madewell is a postdoctoral associate in UF’s department of biostatistics, within the College of Medicine and College of Public Health and Health Professions. Coauthors Ira Longini, Yang Yang, and Natalie Dean, are professors in the biostatistics department and are also affiliated with the Emerging Pathogens Institute.

Their analysis focused on what epidemiologists term the secondary attack rate, or the rate at which a disease spreads from an ill person to others within a family or small group of people living together. They also compared the SARS-CoV-2 secondary attack rate to those known for related coronaviruses, such as Middle East Respiratory Syndrome, or MERS-CoV, and Severe Acute Respiratory Syndrome, or SARS-CoV, which preceded the current pandemic.

Crowded indoor environments where people do not wear cloth face masks are ideal for transmission due to the ease with which the SARS-CoV-2 virus spreads by riding between hosts on respiratory droplets and aerosols. The meta-analysis examined 77,758 participants with confirmed transmission within their households. Patterns uncovered by the researchers include:

  • The estimated SARS-CoV-2 secondary attack rate was 16.6% with 95% confidence interval (14.0%-19.3%), which is higher than observed for SARS-CoV or MERS-CoV.
  • The estimated SARS-CoV-2 secondary attack rate was higher in households with one other contact, 41.5%, than in homes with three or more contacts, 22.8%.
  • The estimated SARS-CoV-2 secondary attack rate was highest to spouses, 37.8%, compared with other household contacts,17.8%.
  • The estimated SARS-CoV-2 secondary attack rate with adult contacts, 28.3%, was higher than compared with child contacts, 16.8%.                                                

Written by: DeLene Beeland