Household Clustering of SARS-CoV-2 in Community Settings: A Study from Rural Ecuador

Abstract

The SARS-CoV-2 pandemic is now expanding into the developing world with devastating consequences. Departing from a population-based study in rural Ecuador where all adult individuals (aged 40 years or older) were tested for SARS-CoV-2 IgG and IgM antibodies, we expanded it to include a house-based case-control component assessing in-house clustering and other variables potentially associated with infection. We selected houses where exactly two study participants lived and were both seropositive (case-houses), and matched 1:1 to control-houses where both were seronegative. Younger household members had an antibody test performed. Infected household members were found in 33 (92%) case-houses and in only six (17%) control-houses. In 28/29 discordant house pairs, the case-house had seropositive household members and the control-house did not (odds ratio: 28; 95% CI: 4.6-1,144). Our data demonstrate strong in-house clustering of infection in community settings, stressing the importance of early case ascertainment and isolation for SARS-CoV-2 control.

Figure 1.

Google map of Atahualpa (Google Earth, Google Inc., Mountain View, CA) showing the distribution of selected houses. Positive case-houses are marked in red, negative case-houses in pink, negative control-houses in blue, and positive control-houses in light blue.

Figure 2.

Flowchart depicting the process of house selection and the reasons for not including potentially eligible houses.

Figure 3.

Serological results of household members of a case-house (left panel) and a control-house (right panel). When both adult members were seropositive (black dots), it was common to observe that younger members were all positive (black stars). The opposite was often seen when adults were both seronegative.