CDC profiles outbreaks linked to untreated recreational water

As many people head to beaches and other bodies of water for the Fourth of July holiday, the US Centers for Disease Control and Prevention (CDC) today provided a snapshot of outbreaks linked to untreated recreational water and said specific steps can minimize the risk of getting sick.

Writing in today's issue of Morbidity and Mortality Weekly Report (MMWR), researchers analyzed 140 outbreaks involving untreated water that occurred between 2000 and 2014, sickening at least 4,958 people from 35 states, 2 of them fatally.

Fecal contamination a common theme

Beaches and public parks containing lakes, reservoirs, and ponds were the leading settings, and of 95 outbreaks with a known cause, 80 were caused by enteric pathogens, which can be transmitted when fecally contaminated water is ingested. The most common ones were norovirus, Escherichia coli, Shigella, and Cryptosporidium. Sources of contamination can include storm water runoff, flooding, sewage overflows, boating waste, or animal waste on or near a beach.

The two deaths were both caused by Naegleria fowleri and were part of the same outbreak. The disease occurs when the ameba present in warm, untreated freshwater, enters the nose and travels to the brain through the olfactory nerve. Though the disease is often fatal, two people recently survived their infections, suggesting that early diagnosis and treatment might improve outcomes, the CDC said.

Swimmer's itch and toxic algae

Other illness sources include avian schistosomes, which can cause "swimmer's itch," and toxins or chemicals, of which the most common type involves toxins from harmful algal blooms. The CDC is seeing more frequent and widespread harmful algal blooms in recent years, possibly because of increasing nutrient pollution, warming water, or improved surveillance. In 2016, the CDC launched an electronic system to help state and territory health officials report illnesses and environmental data specific to the threat. "A better understanding of harmful algal blooms is needed to optimize prevention of associated illness and harmful algal blooms," the authors wrote.

Staying safe in the splash zone

People can minimize their risk by avoiding swimming in untreated water that is shallow, poorly circulating, overcrowded, frequented by children younger than 5 who have limited toilet skills, and in locations that lack accessible well-stocked hygiene facilities, such as diaper-changing stations.

Also, the CDC said swimming after a heavy rain can increase exposure to enteric pathogens. Discolored, smelly, foamy, or scummy water is always a red flag for avoiding swimming, according to the report.

The CDC offered several other tips for preventing exposure to untreated recreational water threats, such as staying out of the water when beaches are closed or if advisories are posted, avoiding swimming or letting sick children swim if they have diarrhea, avoiding swallowing recreational swimming water, and towel drying or showering immediately after getting out of the water.

See also:

Jun 28 MMWR report

Newsletter Sign-up

Get CIDRAP news and other free newsletters.

Sign up now»


Unrestricted financial support provided by

Bentson Foundation Unorthodox Philanthropy logo and text 'Leading Underwriter'3M logoGilead 
Grant support for ASP provided by


  Become an underwriter»