According to a new study, COVID-19 is spreading to American households more often than previously thought.
The study, published Friday (October 30th) in the journal Weekly report on morbidity and mortality, involved 191 people in Tennessee and Wisconsin who lived with someone recently diagnosed with COVID-19. Of these, 102 people became infected within seven days of being included in the study, for a “secondary infection rate” of 53%. (The degree of secondary infection is the percentage of exposed people who catch COVID-19 from the first case.)
About 75% of these secondary infections occurred within five days of the illness of the first member of the household.
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“We observed that after one member of the household became ill, several infections were quickly detected in the household,”
Other studies transmission of COVID-19 in households – mostly in Europe and Asia – have found a secondary infection rate of 30% or less. But the new study, conducted from April to September, was one of the first to systematically look at COVID-19 transmission in US households, with participants taking daily tests for COVID-19.
Part of the reason for the higher rate of secondary infection in the new study, compared to previous reports, may be due to rigorous research methods and follow-up tests of household contacts, the authors say. In addition, studies in other countries may have had lower levels of secondary infection because people in those countries were faster to carry face masks in his own home when another member of the household is ill. (The use of a mask when the patient is traditionally not part of American culturewhile in some other countries.)
The study also found that “significant transmission” occurred regardless of whether the first case of the household (known as the index case) was a child or an adult.
In fact, in households where the index case was under 12 years of age, the secondary infection rate was 53%; and in households where the index patient was between 18 and 49 years old, the secondary infection rate was 55%, the report found.
“The infections happened quickly, whether the first sick member of the household was a child or an adult,” Grizalva said.
Moreover, less than half of household members showed symptoms when tested positive for COVID-19, and 18% remained asymptomatic during the seven-day study. This finding underscores the need for people to be quarantined if they have had close contact with someone who tests positive for COVID-19, the authors say.
In general, “people who suspect they may have COVID-19 should isolate themselves, stay at home, and use a separate bedroom and bathroom if possible,” the report said. This isolation must begin before a person is tested or gets his results. In addition, all members of the household should start wearing a mask in their home, especially in common areas where social distancing it is not possible, the authors said.
The authors note that their study was conducted in two American cities – Nashville, Tennessee and Marshfield, Wisconsin – and the families in the study may not be representative of the total US population.
Originally published in Live Science.