What is cryptosporidiosis?

Cryptosporidiosis is a diarrhoeal disease caused by Cryptosporidium parasites — microscopic protozoa that infect the small intestinal epithelium. In immunocompetent people, it causes self-limiting watery diarrhoea lasting 1-2 weeks. In immunocompromised patients (especially HIV/AIDS), it causes severe, life-threatening chronic diarrhoea. It is transmitted by: contaminated water (including swimming pools — resistant to chlorination); contaminated food; contact with infected animals (calves, lambs — common on farms); person-to-person fecal-oral contact.

Why is cryptosporidiosis dangerous in swimming pools?

Cryptosporidium is uniquely suited to cause swimming pool outbreaks: Oocysts are resistant to standard chlorination (even pools with correct chlorine levels cannot kill Cryptosporidium). An infected person sheds millions of oocysts per bowel movement — and children with diarrhoea or who defecate in the pool are the primary source. The infectious dose is very low (as few as 10 oocysts). Swallowing even a small amount of pool water is enough to cause infection. Prevention: children with diarrhoea or recent diarrhoea should not swim (minimum exclusion 2 weeks after symptoms resolve); don't swallow pool water; shower before entering pool.

Who is at highest risk?

Children under 5 years (especially in LMIC settings — a major cause of childhood malnutrition and stunting); HIV-infected patients with CD4 count below 200 cells/μL (risk of severe, life-threatening chronic cryptosporidiosis — AIDS-defining illness); organ transplant recipients on immunosuppressives; patients with primary immunodeficiency (particularly combined immunodeficiency, CVID, IgA deficiency); travellers to endemic areas; farm workers with animal exposure; swimmers in contaminated pools.

How is cryptosporidiosis treated?

Immunocompetent adults and children: Nitazoxanide (Alinia) — 500mg × 3 days (adults) or age-appropriate dose (children); reduces diarrhoea duration. Supportive: oral rehydration therapy. Immunocompromised patients with HIV: ART (antiretroviral therapy) restoring CD4 >200 cells/μL is the most important treatment — immune reconstitution allows the body to clear the infection. Nitazoxanide has limited efficacy in severe AIDS. Transplant recipients: reduce immunosuppression if possible. No licensed treatment has proven efficacy in severe immunocompromised cryptosporidiosis — research ongoing (halofuginone, paromomycin).

Is cryptosporidiosis present in Georgia?

Yes — Cryptosporidium is present in Georgian water sources, livestock (cattle, sheep, goats are natural reservoirs) and has been documented in human cases, particularly in rural populations. Swimming pool outbreaks are a risk in Georgian recreational water facilities. PHIG monitors waterborne disease outbreaks. The main prevention priorities: UV disinfection of swimming pools (in addition to chlorination), livestock management on farms, and water quality monitoring beyond chlorination in municipal water systems.

How does GMJ News cover cryptosporidiosis?

GMJ News covers WHO cryptosporidiosis data, the swimming pool outbreak challenge (chlorine resistance), HIV/AIDS life-threatening complication, GEMS study childhood burden, nitazoxanide treatment, water treatment (UV vs chlorination), and Georgian waterborne disease surveillance. Cryptosporidiosis is directly relevant to PHIG's water safety, One Health, and hospital infection control programmes.

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Cryptosporidiosis

GMJ News knowledge hub · last reviewed September 2026 · Georgian Medical Journal

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Cryptosporidiosis — caused by the apicomplexan parasites Cryptosporidium parvum (zoonotic, from cattle) and C. hominis (anthroponotic) — is a WHO Neglected Tropical Disease and ECDC notifiable infection causing an estimated 8.7 million diarrhoeal cases per year through contaminated water and food, with a uniquely dangerous property among waterborne pathogens: Cryptosporidium oocysts are highly resistant to chlorine disinfection — the foundation of municipal water treatment — making swimming pools and inadequately filtered water supplies persistent outbreak sources even in high-income countries (WHO). In immunocompromised patients — particularly those with HIV/AIDS (CD4 <200 cells/μL), organ transplant recipients and children with primary immunodeficiencies — cryptosporidiosis causes profuse, life-threatening chronic diarrhoea with associated wasting; in HIV, it was a hallmark AIDS-defining illness before ART.

Key messages

Chlorine-resistant — survives municipal water treatment

Cryptosporidium oocysts are uniquely resistant to chlorine disinfection — the cornerstone of municipal water treatment — making contaminated swimming pools and insufficiently filtered water supplies persistent outbreak sources even in high-income countries. UV and ozone treatment are effective (WHO/ECDC).

8.7M cases/year — massively underreported

WHO estimates approximately 8.7 million cryptosporidiosis cases per year globally; the true burden is much higher due to widespread underreporting, especially as most cases in immunocompetent individuals are not investigated.

Life-threatening in HIV/AIDS (CD4 <200)

In HIV-infected patients with CD4 counts below 200 cells/μL, cryptosporidiosis causes profuse, watery, life-threatening chronic diarrhoea — one of the defining AIDS-related illnesses. ART restoring CD4 counts is the most effective treatment.

Swimming pool outbreaks — the dominant HIC presentation

In HICs, Cryptosporidium is the most common cause of recreational water illness outbreaks — particularly in treated swimming pools, water parks and splash pads. A single infected child can shed billions of oocysts for weeks, contaminating heavily chlorinated pool water.

Nitazoxanide — the only approved treatment in immunocompetent

Nitazoxanide (Alinia) is the only FDA-approved treatment for cryptosporidiosis — effective in immunocompetent adults and children, reducing diarrhoea duration. It has limited efficacy in immunocompromised patients.

WHO NTD — childhood stunting in LMICs

In children in LMICs, repeated Cryptosporidium infections cause malabsorption, nutritional deficiency and growth stunting — contributing to the vicious cycle of poverty, malnutrition and infectious diarrhoea. Cryptosporidiosis is a WHO Neglected Tropical Disease.

Key statistics

~8.7M

cryptosporidiosis cases/year globally (WHO estimate)

WHO

Massively underreported

true burden far exceeds reported cases in most countries

WHO/ECDC

cause of recreational water illness outbreaks in HICs (swimming pools)

CDC/WHO

CD4 <200

HIV threshold for life-threatening chronic cryptosporidiosis

WHO

Resistant

to chlorine disinfection — UV and ozone required for water treatment

WHO

WHO NTD

Cryptosporidiosis is a WHO Neglected Tropical Disease

WHO

Cryptosporidiosis burden by population group — relative risk vs general population (WHO)

Source: WHO. Immunocompromised patients (especially HIV/AIDS) at massively elevated risk.

Glossary of key terms

Cryptosporidium parvum and C. hominis
WHOTwo major human-pathogenic species: C. parvum — zoonotic (cattle primary reservoir); predominant in LMICs and rural settings. C. hominis — anthroponotic (human-to-human); predominant in HIC outbreaks and swimming pool exposures. Morphologically identical; distinguished by PCR/genotyping. Both produce environmental oocysts (4-6 μm) resistant to chlorination.

Oocyst chlorine resistance
WHO/CDCCryptosporidium oocysts are among the most environmentally resistant parasites — surviving standard chlorine concentrations in swimming pools (typically 1-4 mg/L free chlorine) for days. Effective inactivation requires: UV irradiation (40-60 mJ/cm² at 254nm) — the most practical pool treatment; ozone; or hyperchlorination (10-20 mg/L free chlorine for >8 hours — impractical during pool operation). This explains why pool closure and hyperchlorination is required after a confirmed Cryptosporidium-positive bather.

Cryptosporidiosis in HIV/AIDS
WHOIn AIDS patients with CD4 <200 cells/μL, Cryptosporidium causes profuse cholera-like diarrhoea (10-15 litres/day), severe wasting, malabsorption, and can disseminate to biliary tract (cholangiopathy), pancreas, lungs and conjunctiva. ART restoring CD4 >200 cells/μL is the most effective treatment — allowing immune reconstitution to control the infection. Nitazoxanide has limited but some efficacy even in HIV.

Modified acid-fast stain
WHO/DiagnosticThe traditional diagnostic stain for Cryptosporidium in stool — oocysts appear as bright pink/red spheres (4-6 μm) on modified acid-fast (Ziehl-Neelsen) staining. More sensitive alternatives: direct immunofluorescence assay (DFA) using monoclonal antibodies; EIA antigen detection; PCR (most sensitive and allows species differentiation).

GLOBAL Enteric Multicenter Study (GEMS)
Gates Foundation/WHOA landmark multicenter study of 22,568 cases in sub-Saharan Africa and South Asia — the largest diarrhoeal disease study in children. GEMS found Cryptosporidium was the second most common identified cause of moderate-to-severe diarrhoeal disease in children <5 years, and was strongly associated with mortality and growth stunting — establishing cryptosporidiosis as a major childhood killer, not merely an opportunistic infection.

Nitazoxanide (Alinia)
FDA/WHOThe only FDA-approved drug for cryptosporidiosis — a thiazolide antiparasitic. Effective in immunocompetent adults (reduces diarrhoea duration by approximately 2 days) and children (500mg × 3 days for >12 years; 200-400mg × 3 days for children). On WHO Essential Medicines List. Limited efficacy in immunocompromised patients — particularly HIV (some benefit in CD4 >50 cells/μL; minimal benefit in severe AIDS).

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