COVID-19 transmission among households was three times more likely if the household had a high living density, according to a study in Clinical Infectious Diseases.
This means more crowded households are expected to have higher transmission of the SARS-CoV-2 coronavirus. Higher living density in this study is defined as having more than three household members but fewer than six rooms.
The researchers looked at 100 COVID-19 index patients, all adults, and household contacts of all ages from April to October 2020 in North Carolina. Participants were enrolled in the study a median of 6 days after the index patient’s symptom onset or diagnosis.
On days 7, 14, and 21 from symptom onset, the household submitted nasal swabs, and on day 28, they underwent a seroconversion test, although the researchers note that 38% of households did not have complete participation.
Overall secondary attack rate was 32% (95% confidence interval [CI], 22% to 44%). However, it was higher in households with a high living density (51% vs 19%), indicating that those members were 3.3 times more likely to get COVID-19 (95% CI, 1.02 to 10.9). The researchers say this could be a factor in the disproportionate effect of COVID-19 among minorities. For instance, in their cohort, 42% of non-White index patients lived in a higher living density situation vs 12% of White index patients.
The researchers were unable to assess associations with age, mask-wearing, and symptoms during transmission, nor did they analyze index case viral loads.
Household transmission is one of the main drivers of the SARS-CoV-2 pandemic. While masking, physical distancing, and quarantining the whole household may reduce or prevent transmission beyond the household, these strategies are less effective within the household, especially in the setting of high viral load infections and crowded living spaces.*
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Dr. Melvin Sanicas (@Vaccinologist) is a physician-scientist specializing in vaccines, infectious diseases, and global health.