Background: This longitudinal study aimed to clarify the changes in the medical treatment behavior of Japanese patients with chronic diseases during the early phase of the COVID-19 pandemic and examine the factors associated with disease worsening.

Methods: Subjects with chronic diseases were selected from a panel survey that started at the beginning of the COVID-19 pandemic consists of 2,400 participants recruited via the Internet. Medical treatment behaviors (decrease in medical visit frequency, inability to take regular medications, and utilization of telephone/online medical care), psychological distress, and sociodemographic factors were evaluated at baseline (May 2020) and at the follow-up survey (February 2021). A worsening of chronic diseases was defined as those who answered yes to the question, "Has-the-condition-of-the-chronic-disease-worsened?". The factors related to the worsening of chronic diseases at follow-up were examined.

Results: A total of 514 participants (mean age 61.6±12.9 years) were analyzed. The percentage of participants who reported decreasing medical visit frequency was 34% at the baseline and 16.5% at follow-up, and those who reported a worsening of chronic diseases was 5.1% and 5.1%, respectively. A worsening of chronic diseases at follow-up was significantly associated with a younger age, a decreased frequency of medical visits, unemployment, a history of smoking, and psychological distress.

Conclusions: A decreased frequency of medical visits was observed among one-third of the participants with chronic disease in the early stage of the pandemic, and it reduced by half at follow-up. In the early stages of an emerging infectious disease pandemic, decreased regular hospital/clinic visits can lead to a worsening of chronic diseases. Those who had psychological distress, unemployment, and a history of smoking were vulnerable to a worsening chronic disease.