Treated Water Venue: Cryptosporidiosis
Cryptosporidium is an oocyst-forming protozoa that causes a self-limited watery, nonbloody diarrhea which usually resolves within 10-14 days. Most patients have associated abdominal cramps, fever, and vomiting although infected persons can be asymptomatic. Infection in the immunocompromised potentially can lead to profuse and prolonged diarrhea. Oocysts are excreted in the feces of infected hosts and as little as 10 can cause infection. They can survive extreme environmental conditions in water and soil for several months and even survive up to 7 days in a properly chlorinated pool. Transmission occurs between humans via contaminated food and water or from infected animals. Oocysts have been isolated in raw or unpasteurized milk and apple cider. Incidence is highest in children 1 through 4 years of age.
Diagnosis today is usually via molecular methods (nucleic acid amplification tests, aka NAATs), due to their high sensitivity and specificity and is the preferred method. These tests can identify multiple gastrointestinal tract pathogens with a single assay. Diagnosis by microscopy or fecal immunoassay antigens are still available. Treatment is supportive in most cases. If needed, a 3-day course of nitazoxanide can be prescribed. Immunocompromised patients should be managed in consultation with an infectious disease specialist.
Untreated Water Venue: Norovirus
Norovirus is a viral illness characterized by the abrupt onset of vomiting and/or watery diarrhea, usually associated with nausea and abdominal cramps. Symptoms persist 24-72 hours, however they may be prolonged in the immunocompromised and persons at the extremes of the age spectrum. Norovirus has replaced rotavirus as the major cause of medically attended gastroenteritis. While a major cause of recreational water–associated illnesses, high attack rates also occur in semi closed communities including cruise ships, childcare centers, and schools. Transmission is fecal-oral, vomitus oral, person to person, by ingestion of contaminated food and water or touching contaminated surfaces with subsequent touching of the mouth. Asymptomatic viral shedding may occur, especially in children. Prolonged shedding (> 6 mos.) has been reported in immunocompromised hosts.
Molecular diagnosis with stool is utilized most often. Treatment is supportive.
Take Home Message
When evaluating your patients for an acute gastrointestinal illness, consider water-related activities and their potential for being the source. Encourage patients not to ignore posted advisories on beaches, to not swim if they have diarrhea, not to swallow the water they swim in and to minimize water entering their nose while swimming in warm freshwater. If you start seeing several patients with similar symptoms and/or etiology, consider contacting your local or state health department. It could be the beginning of an outbreak.
Dr. Word is a pediatric infectious disease specialist and director of the Houston Travel Medicine Clinic. She has no relevant financial disclosures.
Suggested Readings
Graciaa DS et al. Outbreaks Associated with Untreated Recreational Water — United States, 2000–2014. MMWR Morb Mortal Wkly Rep. 2018 Jun 29;67(25):701-706. doi: 10.15585/mmwr.mm6725a1.
Hlavsa MC et al. Outbreaks Associated with Treated Recreational Water — United States, 2015–2019. MMWR Morb Mortal Wkly Rep. 2021;70:733–738. doi: 10.15585/mmwr.mm7020a1.
Kimberlin DW et al., eds. Red Book Report of the Committee on Infectious Diseases. 33rd ed. American Academy of Pediatrics. 2024. Cryptosporidiosis, p 338-40 and Norovirus, p 622-624.Waterborne Outbreaks Summary Reports. CDC. 2024 April 18.