Seasonal Patterns of Sepsis Incidence and Mortality in the United States: A Nationwide Analysis

Purpose: The aim of this study was to describe seasonal variation in the incidence and outcomes of sepsis in the United States. Methods: This is a retrospective study using National Inpatient Sample database from 2017–2019. Adult sepsis patients were identified based on the CMS SEP-1 measure codes. Monthly sepsis incidence, in-hospital mortality, and organ failure patterns were analyzed. Multivariable logistic regression was used to assess in-hospital mortality by month. We also analyzed the monthly variation in each type of organ failure to uncover patterns that could account for the observed differences in sepsis incidence and outcomes. Main Results: There were 57,019,369 hospitalizations due to sepsis during the study period. The incidence of sepsis hospitalizations was highest in January. January also had the highest in-hospital mortality rate (10.66%), while July had the lowest (8.66%). A multivariable logistic regression analysis showed that January had a significantly higher mortality rate compared to July (odds ratio of 1.22, p < 0.001). The relationship between month and in-hospital mortality for sepsis followed a U-shaped pattern (from January to December), both in raw and adjusted analysis. Respiratory failure similarly followed the U-shaped pattern, with January having the highest incidence, and July and August the lowest. Other organ failures showed consistent patterns throughout the year. The relationship between sepsis due to pneumonia was also U-shaped, especially in the Southern region. Conclusions: This study revealed a U-shaped relationship between both incidence and in-hospital mortality of sepsis, and month throughout the year, with a peak during winter months. Respiratory failure significantly increased in winter, while other organ failures remained constant throughout the year. These data suggest that respiratory infection and respiratory failure appear to mediate the seasonal variation observed in sepsis incidence and mortality, respectively.