Household transmission dynamics of SARS-CoV-2 - The COVID HOME study

Vincenti-Gonzalez, M.F.; Van Der Gun, B.F.T.; Wold, K.I.; Dijkstra, A.E.; Veloo, A.C.M.; Knoester, M.; Huckriede, A.L.W.; Pantano, D.; Niesters, H.G.M.; Friedrich, A.W.; Tami, A.

Abstract

Background Understanding SARS-CoV-2 transmission within restricted indoor areas, such as within households gives detailed insight into transmission dynamics and transmission routes amongst contacts. We aimed to estimate household transmissibility parameters of SARS-CoV-2 and to assess risk factors associated with susceptibility to infection. Methods In March 2020, an ongoing prospective cohort study of non-hospitalised SARS-CoV2 patients began in northern Netherlands. Consenting positive individuals were included in the study along with their household members. Infected individuals were visited weekly at home to obtain clinical data, a nasopharyngeal/throat swab plus stool samples to test for SARS-CoV-2 by qRT-PCR. Participants were followed weekly until day 21 and if still PCR positive, they were sampled for at least two more weeks. A 21-day self-completion questionnaire given to patients recorded sociodemographic data and daily clinical history. Household members were tested for SARS-CoV-2 infection weekly and once positive, followed as described above. All participants were asked to answer questions on knowledge, attitudes and practices (KAP) regarding COVID-19. Secondary attack rates (SAR) (cases occurring following exposure to a primary case) of SARS-CoV-2 in these households and serial intervals (duration between symptom onset of successive cases in a transmission chain) were estimated. Results As of 20-02-2021, a total of 123 participants were included of which 44 were index cases and 79 household contacts. The mean household size was 2.4 persons (range 2-5). A total of 32 households were solely composed by adults (>16 years), while 12 consisted of families with children. The intense follow-up and sampling of household participants allowed to estimate a SAR of 67%. Our current results do not show a difference in SAR between households with or without children (65% vs 68%). Based on transmission chains, the serial interval was estimated to have a mean of 3.5 days (95% confidence interval, 2.0-5.1 days). Causal analysis using Directed Acyclic Graphs including demographics characteristics, KAP and clinical variables is currently being done to assess transmission routes within the household. Conclusions Our results showed a higher estimated SAR compared with previous studies. These preliminary results shed light on the role of the household on the overall community transmission of SARS-CoV-2.