Most people with COVID-19 receive care at home, increasing the likelihood of exposure for household members.
To study the prevalence and characteristics of secondary cases in families after the appearance of a primary case
An observational and retrospective study of families with at least one polymerase chain reaction (PCR) confirmed COVID-19 primary case was conducted from March 15 to December 25, 2020, in a general medicine office in Toledo, Spain. Socio-demographic and clinical variables were compared between primary and secondary cases in the families. The outcome of interest was secondary attack rate of SARS-CoV-2 within the family.
39 families with a primary case (average size 3.4 members) with a total of 132 cohabitants were included. There were 22 cohabitants with negative PCR (22/92 = 24%), 70 secondary cases with positive PCR (Secondary attack rate 76%), of which 25 were asymptomatic (25/70 = 36%), and a cohabiting new-born. A high frequency of people from ethnic minorities, low household income and complex families was found, both in primary and secondary cases. The secondary cases with respect to the primary ones were more women, younger, students and with a lower socio-occupational level, with more asymptomatic cases, and milder symptomatic cases.
In this context, the prevalence of secondary domestic contacts is very high, and it occur in young women, being asymptomatic or mild. The high secondary attack rate suggests the importance of the pre-symptomatic or early symptomatic period of COVID-19, as well as the possible failure to comply with isolation measures.