COVID-19 spreads faster and more widely in U.S. households, finds study

COVID-19 spreads faster and more widely throughout U.S. households than previously reported, according to new preliminary research from a multicenter study led by Vanderbilt University Medical Center researchers and published in MMWR, a weekly report from the Centers for Disease Control and Prevention (CDC).

The study, led by Carlos G. Grijalva, MD, MPH, associate professor of Health Policy, and H. Keipp Talbot, MD, MPH, associate professor of Medicine, found that 51% of others living in the home with someone who was positive for COVID-19 also became infected.

We observed that, after a first household member became sick, several infections were rapidly detected in the household. Those infections occurred fast, whether the first sick household member was a child or an adult."

Carlos G. Grijalva, MD, MPH, Associate Professor of Health Policy

The study found that at least 75% of the secondary household infections occurred within five days of the first person in the household experiencing symptoms.

"This preliminary research is the first to closely follow U.S. households through systematic daily assessments and study the transmission of coronavirus among groups living together under one roof," Talbot said. "Other similar studies have mostly been conducted abroad, and others have made estimates of household transmission using contact tracing data."

Similar studies in the U.S., Europe and Asia have reported that 30%, or less, of household members also became infected.

The preliminary findings from this ongoing study were collected from households in Nashville, Tennessee, and Marshfield, Wisconsin.

Also among the study's findings is that less than half of household members experienced symptoms when they first tested positive, and many reported no symptoms throughout the 7-day daily follow-up period.

The study results underscore the potential for transmission from symptomatic or asymptomatic contact with household members and the importance of quarantine, Grijlava said. Persons aware of recent close contact with an infected person, such as household members, should quarantine at home and monitor for development of symptoms.

As winter approaches, and people start spending more time indoors, it will be important to prepare for potential infections at home.

"In the absence of an efficient approach for identification of infections without regard to symptoms, these findings suggest that prompt adoption of isolation measures as soon as a person feels ill might reduce the probability of household transmission," the authors concluded.