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Florida Health

Disease Control

Cryptosporidiosis in humans is caused by infection with a protozoan parasite called Cryptosporidium parvum.


Oocysts, the infective stage of this parasite, cause an illness that presents as watery diarrhea with abdominal cramps, possibly accompanied by fever, nausea, vomiting, and myalgias. After exposure, the incubation period ranges from 1 to 12 days (median 7 days). In AIDS patients, the illness varies from asymptomatic carriage to severe watery diarrhea with weight loss, electrolyte imbalance and dehydration. Duration of illness can range from days to months, but usually resolves within 2 weeks in otherwise healthy patients. Shedding of oocysts, however, can occur up to 2 weeks after the patient is clinically well. 

Oocysts may be transmitted via contaminated food or water, by direct contact with infected livestock or pets, and from person to person by the fecal-oral route. Cryptosporidium oocysts are present in most surface waters (e.g. rivers, streams, and lakes) throughout the United States, and have shown resistance to chlorine. Oocysts are also difficult to remove by filters. Epidemiological studies have shown that municipal water supplies, camping, swimming, direct contact with feces while caring for an infected person, or association with kittens, puppies and young livestock are the most frequently identified risk factors. 

Cryptosporidiosis in Florida and the U.S. has a seasonal and cyclical trend. Following a sharp increase in cases in 2014 in all genders, races, and ethnicities, cases decreased in 2015, 2016, and 2017. Similar to giardiasis, another parasitic intestinal infection, incidence is highest in 1- to 4-year-olds, followed by infants <1-year-old, then children 5 to 9 years old.

During the past two decades, Cryptosporidium has become recognized as one of the most common causes of waterborne disease (recreational water and drinking water) in humans in the U.S. Cryptosporidiosis incidence peaked in 2014 when there were six waterborne outbreaks investigated, including 134 cases associated with swimming pools, a recreational water park, and kiddie pools. Additional community-wide outbreaks in 2014 were associated with person-to-person transmission and daycares.

There were no food or waterborne disease outbreaks due to Cryptosporidium in 2017. Clusters of illness were reported and associated with person-to-person transmission, travel, and daycares.

Data Summaries for Common Reportable Diseases/Conditions

CDC - Parasites - Cryptosporidium

Current Information

The CDC has recently produced a handbook entitled Cryptosporidium and Water that will help local health departments and water utilities deal with Cryptosporidium in community water supplies.5 Copies can are available online at or may be obtained by writing to: Centers for Disease Control and Prevention, National Center for Infectious Diseases, Division of Parasitic Diseases, Mailstop F-22, 4770 Buford Highway N.E., Atlanta, GA 30341-3724.


  • Klass, J., Cryptosporidium. In Clinical and Pathogenic Microbiology 2nd edition, Howard, BJ, et al., Mosby-Year Book Inc., St. Louis, Mo. 1994; pp. 704-07.

  • Juranek, DD, Cryptosporidiosis: Sources of infection and guidelines for infection prevention. Clinical Infectious Diseases 1995;21(Suppl) S57-61

  • Florida Department of Health, Cryptosporidiosis, Florida Morbidity Statistics.1995 pp. 32-34.

  • CDC, Outbreak of Cryptosporidiosis at a Day Camp-Florida MMWR Vol.45/No.21 May 31,1996;42-44.