Postinfectious Syndromes and Long-Term Sequelae after Giardia Infections, 2025, Miko

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Postinfectious Syndromes and Long-Term Sequelae after <em>Giardia</em> Infections

Syndromes and Sequelae after <em>Giardia</em> Infections
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Volume 32, Supplement—February 2026​


SUPPLEMENT ISSUE

Supplement​

Postinfectious Syndromes and Long-Term Sequelae after​



Shanna Miko, Pallavi A. Kache, Erin Imada, Amy L. Freeland, and Julia C. HastonComments to Author

Author affiliation: Centers for Disease Control and Prevention, Atlanta, Georgia, USA
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Abstract​

Giardiasis, caused by the parasite Giardia duodenalis, is a common infection throughout the world. Acute infections can be asymptomatic, cause mild gastrointestinal symptoms, or be associated with severe, prolonged diarrhea.

Most Giardia infections are self-limiting; however, a subset of symptomatic and asymptomatic persons experience infection-associated chronic conditions that can affect multiple body systems.

Those conditions include stunting and impaired cognitive function in children, irritable bowel syndrome, chronic fatigue, arthritis, and fibromyalgia, all of which can persist for months or years.

Such conditions can impair daily functioning and quality of life; however, research has yet to fully elucidate underlying mechanisms, describe the prevalence, identify persons at increased risk, and develop effective treatment strategies.

We synthesized what is known about giardiasis-associated chronic conditions and illnesses to improve recognition of those complications and ensure appropriate management that can improve the well-being of persons affected.
 

Myalgic Encephalomyelitis or Chronic Fatigue Syndrome​

Myalgic encephalomyelitis or chronic fatigue syndrome (ME/CFS) is characterized by waxing and waning physical, cognitive, or emotional exertion intolerance that is not relieved by sleep or rest (7). Its pathogenesis remains unclear, and the time to onset varies, but the trajectory is similar. A prodromal phase progresses to a nadir, with some level of improvement (35), followed by a chronic phase in which preillness health and abilities are not regained (9). Impairments often are associated with extended leave from work and school (9,26,36). Regardless of symptoms, persons with giardiasis-associated ME/CFS report a negative impact on their quality of life associated with disabilities and disruptions of activities of daily living (6).

Giardiasis-associated ME/CFS was first reported after a 1986 California water contamination event (37). It was again documented after a 2004 water contamination event in Norway (31), when ≈5% of persons developed ME/CFS-like symptoms after giardiasis resolution (36). Two years after the event in Norway, questionnaire respondents reported more fatigue symptoms than gastrointestinal symptoms (31). A follow-up study 3 years postexposure validated the symptoms and identified persons with history of giardiasis as having an increased risk for ME/CFS compared with controls (aRR 4.0; 95% CI 3.5–4.5) (16). At 6 years, the fatigue risk decreased slightly but remained higher compared with unexposed persons (aRR 2.9; 95% CI 2.3–3.4) (17).

The severity of the giardiasis and having >1 treatment course are associated with ME/CFS (26). Chronic fatigue syndrome may also be associated with overactive bladder in both giardiasis-exposed and unexposed persons (OR 2.73, 95% CI 1.85–4.02 in exposed persons; OR 2.79, 95% CI 1.69–4.62 in unexposed persons) (38). Throughout follow-up studies, ME/CFS symptoms are associated with IBS symptoms across all age and sex groups (16,17,39).
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So interesting. I had giardia in 1997 and was so crummy for 2/3 years after that I was sure I still had an active infection... It's when I picked up sun exposure related rashes and worse GI issues that stayed long term.. Tests were always negative.. Very interesting. Thanks for sharing!
 
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