Infection as an exertional heat illness risk factor: a prospective cohort study

Hayley C. Tyson; Michael J. Zurawlew; Megan R. Robinson; Ross Hemingway; Jo Corbett; Mike Tipton; Alexander Andrew Main Gould; Catherine Moore; Rachel Jones; Kathleen Pheasant; Alex Rawcliffe; Rachel Izard; Andrew Roberts; Neil P. Walsh

doi:10.1249/MSS.0000000000004012

Infection as an exertional heat illness risk factor: a prospective cohort study

Hayley C. Tyson
, Michael J. Zurawlew
, Megan R. Robinson
, Ross Hemingway
, Jo Corbett
, Mike Tipton
, Alexander Andrew Main Gould
, Catherine Moore
, Rachel Jones
, Kathleen Pheasant
, Alex Rawcliffe
, Rachel Izard
, Andrew Roberts
, Neil P. Walsh

Research output: Contribution to journal › Article › peer-review

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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 (T_gi, 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 T_gi (+0.3°C, P=0.023). Respiratory infection symptoms were not associated with mild EHI susceptibility.

Conclusion: 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.

Original language	English
Article number	1249
Number of pages	34
Journal	Medicine and Science in Sports & Exercise
Volume	10
DOIs	https://doi.org/10.1249/MSS.0000000000004012
Publication status	Published - 23 Apr 2026

Keywords

heat injury
heat stress
heatstroke
respiratory infection

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10.1249/MSS.0000000000004012

Infection as an exertional heat illness risk factorFinal published version, 753 KBLicence: CC BY-NC-ND

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Tyson, H. C., Zurawlew, M. J., Robinson, M. R., Hemingway, R., Corbett, J., Tipton, M., Gould, A. A. M., Moore, C., Jones, R., Pheasant, K., Rawcliffe, A., Izard, R., Roberts, A., & Walsh, N. P. (2026). Infection as an exertional heat illness risk factor: a prospective cohort study. Medicine and Science in Sports & Exercise, 10, Article 1249. https://doi.org/10.1249/MSS.0000000000004012

@article{4e5445246d494b6a9cbc912de47ba31a,

title = "Infection as an exertional heat illness risk factor: a prospective cohort study",

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. Conclusion: 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.",

keywords = "heat injury, heat stress, heatstroke, respiratory infection",

author = "Tyson, \{Hayley C.\} and Zurawlew, \{Michael J.\} and Robinson, \{Megan R.\} and Ross Hemingway and Jo Corbett and Mike Tipton and Gould, \{Alexander Andrew Main\} and Catherine Moore and Rachel Jones and Kathleen Pheasant and Alex Rawcliffe and Rachel Izard and Andrew Roberts and Walsh, \{Neil P.\}",

year = "2026",

month = apr,

day = "23",

doi = "10.1249/MSS.0000000000004012",

language = "English",

volume = "10",

journal = "Medicine and Science in Sports \& Exercise",

issn = "0195-9131",

publisher = "Lippincott Williams and Wilkins",

}

TY - JOUR

T1 - Infection as an exertional heat illness risk factor: a prospective cohort study

AU - Tyson, Hayley C.

AU - Zurawlew, Michael J.

AU - Robinson, Megan R.

AU - Hemingway, Ross

AU - Corbett, Jo

AU - Tipton, Mike

AU - Gould, Alexander Andrew Main

AU - Moore, Catherine

AU - Jones, Rachel

AU - Pheasant, Kathleen

AU - Rawcliffe, Alex

AU - Izard, Rachel

AU - Roberts, Andrew

AU - Walsh, Neil P.

PY - 2026/4/23

Y1 - 2026/4/23

N2 - 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. Conclusion: 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.

AB - 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. Conclusion: 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.

KW - heat injury

KW - heat stress

KW - heatstroke

KW - respiratory infection

U2 - 10.1249/MSS.0000000000004012

DO - 10.1249/MSS.0000000000004012

M3 - Article

SN - 0195-9131

VL - 10

JO - Medicine and Science in Sports & Exercise

JF - Medicine and Science in Sports & Exercise

M1 - 1249

ER -

Infection as an exertional heat illness risk factor: a prospective cohort study

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