When a person brings Covid-19 home, whether they know they’re infected or not, other people in the household are at risk for contracting the disease. Figuring out the risk level is difficult, but a study announced today by the U.S. Centers for Disease Control and Prevention suggests about half of household members are likely to become infected.
The set of case studies followed people called “contacts” who were living in homes where one person, called the “index patient,” was known to have Covid-19. In all, there were 101 index patients and 191 contacts, none of whom had symptoms when the index patients first became ill. The contacts were aware of the situation, participated in the study, and were trained to self-administer tests for the disease.
The research involved households in Tennessee and Wisconsin who enrolled in the study between April and September. Though the number of people in the study is relatively small, the results offer some insights into what can happen.
Overall, 102 of the 191 household contacts contracted Covid-19, for a secondary infection rate of 53%. About three-fourths of the secondary transmissions were identified within five days, and “substantial transmission occurred whether the index patient was an adult or a child,” the CDC says. For example, the rate was also 53% in the handful of cases in which the index patient was under age 12, and 38% when the index patient was age 12 to 17. The vast majority of index cases — all but 14 of them — were adults.
The results suggest what people should do if they think someone might have brought SARS-CoV-2, the coronavirus that causes Covid-19, into the home:
“Because household transmission of SARS-CoV-2 is common and can occur rapidly after the index patient’s illness onset, persons should self-isolate immediately at the onset of Covid-like symptoms, at the time of testing as a result of a high-risk exposure, or at the time of a positive test result, whichever comes first,” the researchers write. “Concurrent to isolation, all members of the household should wear a mask when in shared spaces in the household.”
There are several other ways to reduce the risk of spreading Covid-19 in the home. Mask-wearing for all is at the top of the list, along with distancing and isolation. But ventilation and air cleaning (with upgraded air filters or air purifiers) are crucial, too.
Medium.***