A household member was defined as someone who was staying in the same living space as the person who tested positive.
‘Household transmission is the main place where most people are getting COVID-19 infection.’
Researchers tested other household members excluding 73 household members who already tested positive for COVID with PCR nasal swabs weekly for three weeks following the initial COVID case, or by a seroconversion antibody test at the fourth week.
“We think this number is actually much higher, sometimes we were getting to households to test people four or five days after the initial COVID-positive person showed symptoms. By that time a lot of household members were already infected. But because that infection happened before we got there, we couldn’t include it in our data” said Jessica Lin, MD, the study’s senior author and assistant professor in the UNC Department of Medicine, Division of Infectious Diseases at the UNC School of Medicine.
This study also took place before the more infectious Delta variant was widely circulating in the U.S.,so the current secondary attack rate in households is significantly higher.
The majority of secondary cases occurred within the first week of the initial positive COVID test. Researchers found that these secondary cases shared a similar nasopharyngeal viral load, or the amount of virus a person had in their nose and throat.
The study also looked at living density – the concentration of people living within a household as a factor that determined whether COVID spread to other household members.
Of the participants enrolled in the study, 44 percent identified as Hispanic or non-white. Researchers found that minority households were more likely to experience a higher living density, and had a higher risk of secondary infection that white households.
These findings show that it is very difficult to follow public health guidelines in some living situations. If many people share common areas or bedrooms, it becomes nearly impossible to isolate or even physical distance.
To avoid this, people in a household should get vaccinated. The chance of secondary COVID infections occurring will be less if vaccinated. A person who has been vaccinated will most likely have a lower viral load, which will make it harder for the virus to infect other household members.