Disease and non-battle injury incidence rate trends in the US military, 2010-2021.

Introduction: This study's purpose was to analyse disease and non-battle injury (DNBI) incidence trends in US military personnel from 2010 to 2021 to understand implications for medical readiness.

Methods: A retrospective cohort of deidentified DNBI cases was developed from the person-event data environment for all military personnel between 2010 and 2021. Chronic and acute conditions were identified using the clinical classification software for categorising International Classification of Disease-9-Clinical Modification (ICD-9-CM) codes and clinical classification software refined for categorising ICD-10-CM codes. The analysis focused on incidence rates (per 10 000 person-years) using negative binomial regression analyses and trend analysis using joinpoint regression to estimate annual percent change (APC) both within the continental US (CONUS) and outside it (OCONUS).

Results: Over 16.9 million person-years were analysed, including CONUS (87.5%) and OCONUS (12.5%). Acute diagnoses comprised 82% of all DNBIs, with the highest rates in musculoskeletal diseases (4494.8 per 10 000), nervous system disorders (2595.7 per 10 000) and non-battle injury (NBI) (2513.1 per 10 000). Chronic mental health disorders had the highest incidence (836 per 10 000) followed by chronic musculoskeletal diseases (661.8 per 10 000). Incidence rates for most diagnosis categories decreased. NBI rates decreased from 2010 to 2021 but most notably for acute NBI from 2018 to 2021 in CONUS (APC=-11.9%) and OCONUS (APC=-13.8%). Infectious disease incidence rates declined until 2019 and were markedly higher in 2020-2021 in CONUS (APC=37.9%) and OCONUS (APC=38.2%), mainly due to COVID-19. Chronic mental health disorder incidence decreased from 2010 to 2021 but acute incidence increased from 2014 to 2021 in both CONUS (APC=20.1%) and OCONUS (APC=19.7%). Incidence of chronic blood diseases increased steadily from 2010 to 2021 in CONUS (APC=3.8%).

Conclusions: Incidence rates for most disease categories decreased from 2010 to 2021. However, increases in the incidence of acute infectious disease during the COVID-19 pandemic, acute mental health disorders and chronic blood diseases reveal growing risks to medical readiness, which may require enhanced surveillance and prevention efforts.