Hospitalized patients with pulmonary tuberculosis in Shizuoka Prefecture in 2009-2020: risk factors for dead cases

Background : Japan had long been a medium-burden country for tuberculosis (TB) but became a low-burden country in 2021. Shizuoka Prefecture is geographically located in Central Japan, and the incidence rate of TB is also at the average level in Japan. This study aimed to understand TB patients' characteristics and risk factors by analyzing the data from 2009 to 2020 in Shizuoka Prefecture, a representative sample for Japan. Methods: We retrospectively collected 1,132 patients with smear-positive pulmonary TB who were admitted to Shimada General Medical Center or Shizuoka General Hospital in the central area of Shizuoka Prefecture from 2009 to 2020. Patients were divided into alive and dead (i.e., all-cause in-hospital death) groups, and clinical parameters were compared between the two groups. Results: The median age of all patients was 80. The number of patients decreased from 2009 to 2020. Moreover, the number of patients over 70 gradually reduced, which was similar for all patients. Immigrant TB patients were 5% of all patients, which was very small compared to the total number of patients. Almost all were from Southeast Asian countries. In multivariate analysis, older age, low body mass index, respiratory failure, low serum albumin, lymphocyte, high serum creatinine levels, and neutrophil were independent prognostic factors. Conclusions: The decline in TB among elderly patients, who comprise most of the population, might be one reason why Japan has become a low-burden country. Although the rate of immigrants is minimal, caution is needed about the increase, especially from Southeast Asian countries. There is a need for a TB medical system that can deal with complications and malnutrition, which are risk factors for death.