Hanevik, Kurt, Kristoffersen, Einar K, Sørnes, Steinar et al. · BMC infectious diseases · 2012 · DOI
This study looked at immune system changes in people who developed chronic fatigue and gut problems after a Giardia infection. Researchers found that people with post-infectious chronic fatigue had lower levels of natural killer (NK) cells, which are important for fighting infections. The more severe someone's fatigue and stomach symptoms were, the lower their NK cells tended to be.
This study provides evidence that post-infectious ME/CFS may involve measurable immune system abnormalities, particularly reduced NK-cell populations that correlate with symptom severity. Identifying specific immune markers could help validate ME/CFS as a biological condition and potentially guide future diagnostic or therapeutic approaches.
This study cannot prove that NK-cell reduction causes ME/CFS symptoms, only that they are associated. The cross-sectional design shows immune differences at one time point (5 years post-infection) and cannot establish whether these changes persist, resolve, or precede symptom onset. Findings are specific to post-infectious cases and may not generalize to ME/CFS of other etiologies.
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 →
Spotted an error in this entry? Report it →