Secondary Attack Rate among Non-Spousal Household Contacts of Coronavirus Disease 2019 in Tsuchiura, Japan, August 2020–February 2021

• Published in: International journal of environmental research and public health Vol. 18; no. 17; p. 8921
• Main Authors: Ogata, Tsuyoshi, Irie, Fujiko, Ogawa, Eiko, Ujiie, Shifuko, Seki, Aina, Wada, Koji, Tanaka, Hideo
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 25.08.2021; MDPI
• Subjects: Antigens; Contact tracing; Coronaviruses; COVID-19; Delay; Diagnostic systems; Disease transmission; Households; Infections; Infectious diseases; Jurisdiction; Multivariate analysis; Nurses; Patients; Public health; Risk analysis; Risk factors; Severe acute respiratory syndrome coronavirus 2; China; Japan
• ISSN: 1660-4601; 1661-7827; 1660-4601
• DOI: 10.3390/ijerph18178921

Household secondary attack rate (HSAR) by risk factor might have a higher transmission rate between spouses. We investigated risk factors for the HSAR among non-spousal household contacts of patients with coronavirus disease 2019 (COVID-19). We studied household contacts of index cases of COVID-19 in Tsuchiura, Japan, from August 2020 through February 2021. The HSARs of the whole household contacts and non-spousal household contacts were calculated and compared across risk factors. We used a generalized linear mixed regression model for multivariate analysis. We enrolled 496 household contacts of 236 index COVID-19 cases. The HSAR was higher for spousal household contacts (37.8%) than for other contacts (21.2%). The HSAR was lower for non-spousal household contacts with a household size (number of household members) of two (18.2%), compared to the HSAR for contacts with a household size ≥4. The HSAR was higher for non-spousal household contacts of index patients with ≥3 days of diagnostic delay (period between onset and diagnosis) (26.0%) compared to those with ≤2 days’ delay (12.5%) (p = 0.033). Among non-spousal household contacts, the HSAR was low for those with a household size of two and was high for contacts of index patients with a long diagnostic delay.