Estimation of seroprevalence of novel coronavirus disease (COVID-19) using preserved serum at an outpatient setting in Kobe, Japan: A cross-sectional study

Asako Doi; Kentaro Iwata; Hirokazu Kuroda; Toshikazu Hasuike; Seiko Nasu; Aya Kanda; Tomomi Nagao; Hiroaki Nishioka; Keisuke Tomii; Takeshi Morimoto; Yasuki Kihara

doi:10.1016/j.cegh.2021.100747

Estimation of seroprevalence of novel coronavirus disease (COVID-19) using preserved serum at an outpatient setting in Kobe, Japan: A cross-sectional study

Clin Epidemiol Glob Health. 2021 Jul-Sep:11:100747. doi: 10.1016/j.cegh.2021.100747. Epub 2021 Apr 19.

Authors

Asako Doi^{1

2}, Kentaro Iwata³, Hirokazu Kuroda^{1

2}, Toshikazu Hasuike^{1

2}, Seiko Nasu^{1

4}, Aya Kanda⁴, Tomomi Nagao⁴, Hiroaki Nishioka², Keisuke Tomii⁵, Takeshi Morimoto⁶, Yasuki Kihara⁷

Affiliations

¹ Department of Infection Control, Kobe City Medical Center General Hospital, Chuoku, 6500047, Kobe, Hyogo, Japan.
² Department of Infectious Diseases, Kobe City Medical Center General Hospital, Chuoku, 6500047, Kobe, Hyogo, Japan.
³ Division of Infectious Diseases Therapeutics, Kobe University Graduate School of Medicine, Chuoku, 6500017, Kobe, Hyogo, Japan.
⁴ Department of Laboratory Medicine, Kobe City Medical Center General Hospital, Chuokum, 6500047, Kobe, Hyogo, Japan.
⁵ Department of Respiratory Medicine, Kobe City Medical Center General Hospital, Chuoku, 6500047, Kobe, Hyogo, Japan.
⁶ Department of Clinical Epidemiology, Hyogo Medical College, Mukogawa, 6638501, Nishinomiya, Hyogo, Japan.
⁷ Kobe City Medical Center General Hospital, Chuoku, 6500047, Kobe, Hyogo, Japan.

Abstract

Objectives: Coronavirus disease 2019 (COVID-19) pandemic caused by SARS-CoV-2 has been affecting many people on earth and our society. Japan is known to have relatively smaller number of its infections as well as deaths among developed nations. However, accurate prevalence of COVID-19 in Japan remains unknown. Therefore, we conducted a cross-sectional study to estimate seroprevalence of SARS-CoV-2 infection.

Methods: We conducted a cross-sectional serologic testing for SARS-CoV-2 antibody using 1000 samples from patients at outpatient settings who visited the clinic from March 31 to April 7, 2020, stratified by the decade of age and sex.

Results: There were 33 positive IgG among 1000 serum samples (3.3%, 95%CI: 2.3-4.6%). By applying this figure to the census of Kobe City (population: 1,518,870), it is estimated that the number of people with positive IgG be 50,123 (95%CI: 34,934-69,868). Age and sex adjusted prevalence of positivity was calculated 2.7% (95%CI: 1.8-3.9%), and the estimated number of people with positive IgG was 40,999 (95%CI: 27,333-59,221). These numbers were 396 to 858-fold more than confirmed cases with PCR testing in Kobe City.

Conclusions: Our cross-sectional serological study suggests that the number of people with seropositive for SARS-CoV-2 infection in Kobe, Japan is far more than the confirmed cases by PCR testing.

Keywords: Coronavirus disease 2019 (COVID-19); SARS-CoV-2; Seroprevalence.