Explained: How SARS-CoV-2 behaves in a household setting

What the study says

In the study, researchers collected data from two local hospitals in China between January 1 and February 20, 2020. Eligible households were defined as those where only one family member, called the index patient, had a clear history of exposure to Wuhan or people from Wuhan or high-risk sites such as hospitals, supermarkets or railway stations within 14 days before illness onset. Further, all family members resided in one house till the time the index patient was tested positive for COVID-19.

Secondary attack rate within the household

Out of a total of 392 household contacts and 105 index patients studied, the secondary attack rate of SARS-CoV-2 was 16.3 per cent. Secondary attack rate refers to the proportion of infected household contacts, excluding the index patient.

The study concludes that this secondary attack rate is the higher than SARS and MERS, and than that of pandemic influenza A in 2009, which was at 13 per cent. “This might contribute to the dramatically higher number of infected cases than the two other coronaviruses related diseases,” they note.

Further, the time and chance of getting the disease from an infected person is more within a household than in the community or at the population-level. Therefore, this could mean that the transmission probability is higher in the household model.

Transmission dynamics within the household

Significantly, in this model, researchers found that the secondary attack rate was “dramatically” higher for adults than children, which might indicate that adults are more susceptible to the disease than children below the age of 18 when they were exposed to the same sources of infection.

However, while research on the virus is continuously evolving, various studies note that while people of all age groups are susceptible, they may suffer different severities due to the disease depending on their age and if they have any comorbidities such as hypertension, diabetes or heart disease.

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“However, the real causes leading to the different secondary attack rates between adult and children needed to be more explored and many factors could influence the secondary transmission of epidemic diseases in the household, such as behaviors of contacts and occupations of members,” researchers have said.

Further, the secondary attack rate was higher for spouses of index patients than other family members, which might be the case because spouses are exposed to index patients for a longer duration, especially if they stay in the same room.

Effects of self-quarantine at home

Researchers found that the 105 index patients who were quarantined at home for 14 days immediately after the onset of symptoms infected no other members of the household, provided they were wearing masks and residing alone.

“This indicated that home quarantine by themselves since onset of symptoms might make certain sense to prevent the transmission of SARS-CoV-2 in household,” the study says.

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