A low proportion of asymptomatic COVID-19 patients with the Delta variant infection by viral transmission through household contact at the time of confirmation in Ibaraki, Japan

Tsuyoshi Ogata; Hideo Tanaka; Fujiko Irie; Yumiko Nozawa; Etsuko Noguchi; Kayoko Seo; Emiko Tanaka

doi:10.35772/ghm.2021.01116

A low proportion of asymptomatic COVID-19 patients with the Delta variant infection by viral transmission through household contact at the time of confirmation in Ibaraki, Japan

Glob Health Med. 2022 Jun 30;4(3):192-196. doi: 10.35772/ghm.2021.01116.

Authors

Tsuyoshi Ogata¹, Hideo Tanaka², Fujiko Irie³, Yumiko Nozawa¹, Etsuko Noguchi¹, Kayoko Seo¹, Emiko Tanaka¹

Affiliations

¹ Itako Public Health Center of Ibaraki Prefectural Government, Itako, Japan.
² Fujiidera Public Health Center of Osaka Prefectural Government, Fujiidera, Japan.
³ Tsuchiura Public Health Center of Ibaraki Prefectural Government, Tsuchiura, Japan.

Abstract

We conducted a study to investigate the proportion of patients with asymptomatic coronavirus disease 2019 (COVID-19) infected with the Delta variant compared with those infected with the wild-type strain at the time of confirmation. A total of 504 patients with confirmed severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection by viral transmission through household contact in Ibaraki, Japan were included. The proportion of asymptomatic COVID-19 patients at the time of confirmation was compared between patients infected with L452R mutation strain from June to September 2021 and those infected with the wild-type strain from November 2020 to January 2021, and was found to be 14.2% and 28.8%, respectively (relative risk, 0.49; 95% confidence interval, 0.35-0.70). The proportion of asymptomatic COVID-19 patients by viral transmission through household contact was lower among the Delta variant than those among the wild-type strain at the time of confirmation. It might contribute to attenuation of transmission.

Keywords: Delta variant; Japan; asymptomatic; coronavirus disease 2019 (COVID-19).

2022, National Center for Global Health and Medicine.