CDC Warns of Recent Jump in Cryptosporidiosis Outbreaks

Agency Offers Resources to Promote Healthy, Safe Swimming

June 06, 2017 11:02 am News Staff
[Young girl sitting poolside]

Each year, Memorial Day signals the unofficial start of summer, with swimming pools, water parks and other aquatic attractions opening all across country. To ensure fun in the sun doesn't turn into a trip to the doctor's office -- or worse -- the CDC is emphasizing the importance of proper swimming hygiene and sharing healthy swimming resources that clinicians can pass along to patients.

According to a May 19 article in Morbidity and Mortality Weekly Report (MMWR)( that describes a recent national uptick in recreational water-associated disease outbreaks caused by the parasite Cryptosporidium, engaging swimmers in prevention efforts -- rather than taking remedial action after contamination occurs -- is key to avoiding these outbreaks.

In short, said Michele Hlavsa, R.N., M.P.H., chief of the CDC's Healthy Swimming Program in a May 18 CDC news release,( "To help protect your family and friends from Crypto and other diarrhea-causing germs, do not swim or let your kids swim if sick with diarrhea."

Story Highlights
  • A May 19 article in Morbidity and Mortality Weekly Report describes a recent national uptick in recreational water-associated disease outbreaks caused by the parasite Cryptosporidium.
  • In response, the CDC is emphasizing the importance of proper swimming hygiene and sharing healthy swimming resources that clinicians can pass along to patients.
  • Simple prevention messages such as "Don't swim while ill with diarrhea" and "Don't swallow the water" can help keep patients safe and healthy this summer.

Furthermore, she cautioned, "Protect yourself from getting sick by not swallowing the water in which you swim."

Focus on Outbreaks in Three States

Overall, the MMWR article notes, as of Feb. 24, 2017, 13 of 24 states that reported provisional data for 2016 identified at least 32 aquatic facility-associated cryptosporidiosis outbreaks. By comparison, 20 such outbreaks were reported to CDC via the National Outbreak Reporting System for 2011, 16 for 2012, 13 for 2013 and 16 for 2014.

In addition to highlighting specific cryptosporidiosis outbreaks associated with aquatic facilities in Alabama, Arizona, and Ohio in 2016, the MMWR report illustrates the use of CryptoNet, the first molecularly based surveillance system for a parasitic disease in the United States. By elucidating Cryptosporidium chains of transmission and clarifying the epidemiology of cryptosporidiosis, CryptoNet data should prove helpful in devising and optimizing evidence-based prevention strategies.

Here's a brief review of the MMWR report's findings:

Alabama: On Aug. 12, 2016, the Alabama Department of Public Health received a report of 35 individuals who developed gastrointestinal (GI) symptoms after visiting a single aquatic facility. Additional case-finding activities identified 23 outbreak-associated cases. Three patients were found to have laboratory-confirmed Cryptosporidium infection; molecular characterization by CryptoNet of one of these specimens identified it as the C. hominis IfA12G1R5 subtype. Data collected from 15 patients indicated the median incubation period was eight days after visiting the aquatic facility on July 31.

Arizona: That same month, Arizona public health officials were notified about a cluster of GI illness cases affecting members of a Little League team and their family members. According to patient reports, 36 people became ill within six or seven days of visiting the same recreational water facility in Maricopa County on July 22. Molecular characterization of four specimens again identified the C. hominis IfA12G1R5 subtype. Further efforts to determine the magnitude of the outbreak revealed that from July 1-Oct. 31, 2016, a total of 352 laboratory-confirmed cryptosporidiosis cases were detected statewide, compared with an annual median of 46 cases detected from 2011 to 2015. Of 317 patients who were interviewed, 204 reported recreational water exposure at various public aquatic venues, with dozens of interviewees saying they swam at one or more facilities while symptomatic.

Ohio: From 2012 through 2015, the Ohio Department of Health and local public health departments detected a median of 399 cryptosporidiosis cases each year across the state. In 2016, that incidence spiked nearly fivefold to 1,940 cases. Ten of 24 cryptosporidiosis outbreaks detected throughout the state that year were associated with aquatic venues. This time, CryptoNet identified the C. hominis IdA19 subtype, which has rarely been seen in the United States, in a number of specimens.

According to the report's authors, "The emergence of Cryptosporidium as the leading etiology of aquatic facility-associated outbreaks results from the parasite's extreme chlorine tolerance." Whereas free available chlorine administered at CDC-recommended concentrations (i.e., at least 1 part per million) inactivates most infectious organisms within minutes, CDC researchers demonstrated in a 2015 study that Cryptosporidium oocysts can survive in such an environment for days, in large part due to a highly chlorine-resistant outer shell.

It was this very finding that last year led the agency to issue revised recommendations for hyperchlorination( when responding to diarrheal incidents in public aquatic venues (i.e., high-risk Cryptosporidium contamination events) and aquatic facility-associated cryptosporidiosis outbreaks.

Health Swimming Resources for Patients

Still, as the old adage goes: An ounce of prevention is worth a pound of cure. To that end, the CDC offers a comprehensive collection of information( for various audiences, including medical professionals, public health officials and swimmers.

Resources for physicians( include educational materials developed by the CDC and other partners that can be used when instructing patients about proper water hygiene practices.

For starters, the agency offers these five simple messages physicians can share with patients:

  • Don't swim while ill with diarrhea.
  • For patients with cryptosporidiosis, don't swim for an additional two weeks after diarrhea has resolved.
  • Don't swallow the water.
  • Keep ears as dry as possible, and dry them thoroughly after swimming.
  • Don't swim when you have open wounds.

A wide range of statistical and other data-based publications( also are available from the CDC so clinicians can gauge for themselves the extent of the problem posed by waterborne illnesses.

Finally, the agency has assembled a diverse collection of promotional resources and tools( that includes brochures( that can be handed out to patients or posted in exam rooms, buttons and banners( for use on physicians' practice websites, infographics( encouraging healthy swimming behaviors, posters( on swimming-related topics, and much more.

Related AAFP News Coverage
Cryptosporidiosis Outbreaks on the Rise, CDC Warns
Educate Patients on How to Best Avoid Pool-related Illnesses


Help Your Patients Prepare for a Safe Summer
AAFP Resource Offers Tips for Hydration, Sun Protection and Pool Safety


More From AAFP
American Family Physician: Recreational Waterborne Illnesses: Recognition, Treatment, and Prevention

American Family Physician: Information from Your Family Doctor: Waterborne Illnesses

Additional Resource
CDC: Parasites - Cryptosporidium (also known as "Crypto")(