Predictors of somatic symptoms during the COVID-19 pandemic: a national longitudinal survey in Japan

Abstract

Objectives: The COVID-19 pandemic has highlighted the long-term consequences of SARS-CoV-2 infection, termed long COVID. However, in the absence of comparative groups, the differentiation of disease progression remains difficult, as COVID-19 symptoms become indistinguishable from symptoms originating from alternative etiologies. This study aimed to longitudinally investigate the association between COVID-19 exposure and the somatic symptoms in the Japanese general population.

Design: This was a longitudinal cohort study with 1-year follow-up.

Setting and participants: Longitudinal data from 19 545 individuals who participated in the Japan Society and New Tobacco Internet Survey (JASTIS) 2022 and 2023 were included. In this study, we used data from the 2022 JASTIS as baseline data and the 2023 JASTIS as follow-up data. Based on questionnaire responses, respondents were classified into three categories of exposure to COVID-19.

Outcome measures: The somatic symptoms were assessed by the Somatic Symptom Scale-8 (SSS-8). Using generalised linear models adjusted for baseline covariates, we calculated the ORs of having very high somatic symptoms assessed by SSS-8, attributable to COVID-19 exposure (no COVID-19 cases as the reference group).

Results: Follow-up completers were divided into three groups according to COVID-19 exposure (no COVID-19, n=16 012; COVID-19 without O2 therapy, n=3201; COVID-19 with O₂ therapy, n=332). After adjusting for all covariates, COVID-19 cases with O₂ therapy had a significant positive association (OR 7.60, 95% CI 5.47 to 10.58) with a very high somatic symptoms burden while other COVID-19 exposure groups did not. Pre-existing physical and psychological conditions were also associated with increased risk of somatic symptoms.

Conclusion: The findings of our study suggest that the severity of COVID-19 symptoms requiring O₂ therapy in the acute phase led to high somatic symptoms. Pre-existing conditions were also associated with a subsequent risk of somatic symptoms.

Keywords: COVID-19; EPIDEMIOLOGY; Public health.