E2 ModerateModerate confidencePEM unclearCase-ControlPeer-reviewedReviewed
Risk markers for both chronic fatigue and irritable bowel syndromes: a prospective case-control study in primary care.
Hamilton, W T, Gallagher, A M, Thomas, J M et al. · Psychological medicine · 2009 · DOI
Quick Summary
This study looked at whether ME/CFS and irritable bowel syndrome (IBS) share common triggers or underlying causes. Researchers compared nearly 4,400 patients with fatigue syndromes to two control groups and found that infections—especially viral infections—appeared before ME/CFS developed, while stomach infections were more common before IBS. The findings suggest that while both conditions may have similar predisposing factors, the specific triggers that cause them to develop are different.
Why It Matters
Understanding whether ME/CFS and IBS share common roots helps explain why many patients experience both conditions simultaneously. By distinguishing between predisposing factors (long-standing vulnerabilities) and triggering factors (events that precipitate illness), this study provides clues about the underlying mechanisms of ME/CFS and may eventually inform prevention and treatment strategies.
Observed Findings
- Viral infections were a significant recent risk marker for fatigue syndromes, with stronger associations the closer the infection occurred to diagnosis (odds ratios 2.3–6.3)
- Gastroenteritis conferred greater risk for IBS than for fatigue syndromes
- CFS shared more distant predisposing risk markers with IBS than other fatigue syndromes, including depressive disorders (OR 2.3–2.4) and other symptom-based disorders (OR 3.8)
- Viral infections were a more prominent recent risk marker for CFS (OR 2.8) compared to IBS
- Both conditions appeared to have common predisposing factors but different triggering mechanisms
Inferred Conclusions
- Fatigue syndromes and IBS are heterogeneous conditions with partially overlapping predisposing factors, suggesting a shared underlying predisposing pathophysiology
- CFS in particular shares predisposing risk markers with IBS, supporting the hypothesis that both may arise from similar constitutional vulnerabilities
- The different triggering factors (viral infection for fatigue syndromes, gastroenteritis for IBS) suggest distinct precipitating mechanisms despite shared predisposition
- Psychiatric and somatic comorbidities in the years before diagnosis may identify patients at risk for developing these conditions
Remaining Questions
What This Study Does Not Prove
This study does not prove that infections cause ME/CFS or IBS—it shows only temporal association. The study cannot establish why some people develop these conditions after infection while others do not, nor does it identify the biological mechanisms connecting infections to disease development. Additionally, findings are limited to patients who sought primary care, potentially missing undiagnosed cases.
Tags
Symptom:Fatigue
Phenotype:Infection-Triggered
Method Flag:PEM Not DefinedWeak Case DefinitionMixed Cohort
Metadata
- DOI
- 10.1017/S0033291709005601
- PMID
- 19366500
- Review status
- Editor reviewed
- Evidence level
- Single-study or moderate support from human research
- Last updated
- 12 April 2026
About the PEM badge: “PEM required” means post-exertional malaise was an explicit required diagnostic criterion for participant inclusion in this study — not that PEM was studied, observed, or discussed. Studies using criteria that do not require PEM (e.g. Fukuda, Oxford) are tagged “PEM not required”. How the atlas works →
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