biostudies-literatureLewandowski SANational Institute of Environmental Health SciencesNIEHS NIH HHSAndrew and Corey Morris-Singer Foundatione0263803https://www.ebi.ac.uk/biostudies/studies/S-EPMC9683623biostudies-literatureUnknown17(11)This study characterized associations between annually scaled thermal indices and annual heat stress illness (HSI) morbidity outcomes, including heat stroke and heat exhaustion, among active-duty soldiers at ten Continental U.S. (CONUS) Army installations from 1991 to 2018. We fit negative binomial models for 3 types of HSI morbidity outcomes and annual indices for temperature, heat index, and wet-bulb globe temperature (WBGT), adjusting for installation-level effects and long-term trends in the negative binomial regression models using block-bootstrap resampling. Ambulatory (out-patient) and reportable event HSI outcomes displayed predominately positive association patterns with the assessed annual indices of heat, whereas hospitalization associations were mostly null. For example, a one-PloS oneHeat stress illness outcomes and annual indices of outdoor heat at U.S. Army installations.PMC9683623T32 ES007322Shaman JLLewandowski SAKioumourtzoglou MAfalseHeat stress illness outcomes and annual indices of outdoor heat at U.S. Army installations.This study characterized associations between annually scaled thermal indices and annual heat stress illness (HSI) morbidity outcomes, including heat stroke and heat exhaustion, among active-duty soldiers at ten Continental U.S. (CONUS) Army installations from 1991 to 2018. We fit negative binomial models for 3 types of HSI morbidity outcomes and annual indices for temperature, heat index, and wet-bulb globe temperature (WBGT), adjusting for installation-level effects and long-term trends in the negative binomial regression models using block-bootstrap resampling. Ambulatory (out-patient) and reportable event HSI outcomes displayed predominately positive association patterns with the assessed annual indices of heat, whereas hospitalization associations were mostly null. For example, a one-2022-01-01T00:00:00Z20222025-04-05T14:41:20.181Z2025-04-05T14:41:20.181ZS-EPMC96836233641734210.1371/journal.pone.0263803