Coronavirus household transmission much higher than previously thought, new study suggests

  • Transmission of the Covid-19 virus in households is occurring at higher rates than previously thought
  • These findings emerged after a study by researchers from the CDC tracked household cases in the US
  • The evidence indicate that mask-wearing in households, especially where physical distancing is hard, should be implemented

Individuals who develop Covid-19 end up infecting around half of their household members with SARS-CoV-2, a US study by the Centers for Disease Control and Prevention (CDC) has found.

The study’s findings also revealed that adults are only slightly more likely than children to spread the virus, which differs from previous research suggesting that adults are bigger drivers than children.

According to their paper, transmission of the new coronavirus occurring within households is well known; however, the data on transmission from children are limited.

The research involved finding index cases (the first household case) of patients with lab-confirmed SARS-CoV-2 infection among 191 people in Nashville, Tennessee, and Wisconsin who lived with someone recently diagnosed with Covid-19.

The study was published in the journal Morbidity and Mortality Weekly Report.

'Infections occurred fast'

In an attempt to quantify Covid-19’s household transmission rate, the CDC researchers had both the index patients and their household members complete symptom diaries.

They also obtained specimens (either nasal swabs only or nasal swabs and saliva samples) for 14 days.

Of these participants, 102 people developed Covid-19 within seven days of being enrolled in the study, for a secondary infection rate of 53%. The secondary infection rate is the percentage of exposed people who catch Covid-19 from the primary case.

About 75% of these secondary infections occurred within five days of the first household patient’s illness onset.

"We observed that, after a first household member became sick, several infections were rapidly detected in the household," study lead author Dr Carlos Grijalva, an associate professor of Health Policy at Vanderbilt University Medical Center in Nashville, said in a statement reported by EurekAlert.

The secondary infection rate when index patients were over 18 was 57%. This dropped slightly to 43% when the index patient was under the age of 18.

The study also found that “substantial transmission occurred whether the index patient was an adult or a child”.

"Infections occurred fast, whether the first sick household member was a child or an adult," Grijalva said.

'Wear masks within shared spaces in the household'

The researchers also noted that fewer than half of household participants showed symptoms at the time they tested positive for Covid-19, and that 18% remained asymptomatic over the seven-day study period.

This finding also proves the importance of people quarantining if they've had close contact with someone testing positive for Covid, the authors wrote.

“Because prompt isolation of persons with Covid-19 can reduce household transmission, persons who suspect that they might have Covid19 should isolate, stay at home, and use a separate bedroom and bathroom if feasible,” the report said.

In fact, the authors suggest that isolation should begin before a person gets tested or gets their results, and that all household members should start wearing a mask in their home, particularly in shared spaces where appropriate physical distancing isn't possible.

READ | Many Covid-19 cases are asymptomatic - but how does this happen?

READ | Leading Covid-19 vaccine candidate to be manufactured in SA

READ | More evidence masks slow Covid spread

Image: Getty/gilaxia

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