Infection as an Exertional Heat Illness Risk Factor: A Prospective Cohort Study

Tyson, HC, Zurawlew, MJ ORCID: 0000-0003-3608-1028, Robinson, MR, Hemingway, R, Corbett, J, Tipton, MJ, Gould, AAM, Moore, C, Jones, R, Pheasant, K, Rawcliffe, AJ, Izard, RM, Roberts, AJ and Walsh, NP ORCID: 0000-0002-3681-6015 (2026) Infection as an Exertional Heat Illness Risk Factor: A Prospective Cohort Study. Medicine and Science in Sports and Exercise. ISSN 0195-9131

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Abstract

Purpose:
Strenuous physical activity for work or leisure increases the risk of exertional heat illness (EHI), which can be fatal. Respiratory infection may increase EHI risk, but empirical evidence is equivocal and relies upon clinical case reviews that lack objective measures and comparator controls. This prospective cohort study investigated the association between respiratory infection and EHI.

Methods:
N=807 UK infantry recruits (M=805/F=2) completed a 6.4-mile loaded march between Spring and Fall (2021-2024, WBGT, 11.2 ± 3.6°C). Participants completed the Jackson Common Cold Questionnaire on each of the 3 days preceding and before the loaded march on Day 0. Additional measures included clinical pathology on throat swabs (Day -3 and -1), serum C-reactive protein (CRP; Day -1) and gastrointestinal temperature (Tgi, Day 0). EHI was classified as mild (exercise-induced headache, dizziness, or nausea) or severe (CNS disturbance plus hyperthermia and/or end-organ damage). Logistic regression examined the association between respiratory infection and EHI after full adjustment for widely considered EHI risk factors.

Results:
N=118 participants were classified as mild (15%) and N=40 as severe EHI (5%). The likelihood of severe EHI was increased four-fold with respiratory infection symptoms on Day -1 and 0 (OR=4.09, 95% CI=1.29–12.90, P=0.016) and three-fold when restricting analysis to symptoms on Day 0 (OR=2.83, 95% CI=1.02–7.86, P=0.046). Participants with respiratory infection symptoms exhibited increased pathogen expression, systemic inflammation (CRP >3 mg·L -1) and pre-loaded march Tgi (+0.3°C, P=0.023). Respiratory infection symptoms were not associated with mild EHI susceptibility.

Conclusions:
Ongoing respiratory infection was associated with an increased likelihood of severe exertional heat illness. Individuals at risk of exertional heat illness (e.g., athletes) should avoid strenuous physical activity when suffering respiratory infection symptoms.

Item Type:	Article
Uncontrolled Keywords:	HEAT INJURY; HEAT STRESS; HEATSTROKE; RESPIRATORY INFECTION; 32 Biomedical and Clinical Sciences; 3202 Clinical Sciences; 42 Health Sciences; Prevention; Physical Activity; Lung; Infectious Diseases; Biodefense; 1106 Human Movement and Sports Sciences; 1116 Medical Physiology; 1117 Public Health and Health Services; Sport Sciences; 3202 Clinical sciences; 3208 Medical physiology; 4207 Sports science and exercise
Subjects:	R Medicine > RC Internal medicine > RC1200 Sports Medicine
Divisions:	Sport and Exercise Sciences
Publisher:	Wolters Kluwer Health
Date of acceptance:	26 March 2026
Date of first compliant Open Access:	11 June 2026
Date Deposited:	11 Jun 2026 09:11
Last Modified:	11 Jun 2026 10:14
DOI or ID number:	10.1249/MSS.0000000000004012
URI:	https://researchonline.ljmu.ac.uk/id/eprint/28807

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