CDC Reports Outbreaks Associated With Untreated Recreational Water on the Rise: An Overview of the CDC’s Morbidity and Mortality Weekly Report

The Morbidity and Mortality Weekly Report (MMWR) is a weekly epidemiological digest for the United States published by the Centers for Disease Control and Prevention (CDC). It is considered by many practicing in the public health sector to be the primary publication for sharing public health information and recommendations that have been received by the CDC from state health departments.

Recently, The Environmental Law Monitor reported on the May 18, 2018 CDC Report: “Outbreaks Associated with Treated Recreational Water – United States, 2000-2014. The MMWR report assimilated outbreak data associated with treated recreational water from public health officials from 46 states and Puerto Rico for the period of 2000 through 2014. On June 29, 2018, The CDC complemented its May report with a review of assimilated outbreak data associated with untreated recreation water sources such as  lakes, rivers and oceans. The survey reviewed data from the 35 states and Puerto Rico during 2000 to 2014.

The data documented 140 outbreaks resulting in 4,958 cases and two deaths. Ninety five of the outbreaks were confirmed to be of infectious etiology. Among these, enteric pathogens (those affecting the intestines) caused 80 (84 percent); 21 (22 percent) were caused by norovirus, 19 (20 percent) by Escherichia coli, 14 (15 percent) by Shigella, and 12 (13 percent) by Cryptosporidium. Investigations of these 95 outbreaks identified 3,125 cases: 2,704 (87 percent) were caused by enteric pathogens, including 1,459 (47 percent) by norovirus, 362 (12 percent) by Shigella, 314 (10 percent) by Cryptosporidium, and 155 (5 percent) by E. coli. Avian schistosomes (birdborne parasites) were identified as the cause of 345 (11 percent) of the 3,125 cases. The two reported deaths arose from a single outbreak caused by Naegleria fowleri (brain eating ameba). Of the 103 outbreaks with confirmed etiology, 8 (8 percent) were caused by toxins or chemicals. Seven of the 8 outbreaks caused by toxins were traced to algal toxins from harmful algal blooms.

Public parks (36 percent) and beaches (32 percent) were the leading settings associated with the 140 outbreaks, most of which were associated with lakes, reservoir or pond venues. As might be expected, the majority of the outbreaks (84 percent) occurred between June and the end of August, with almost 60 percent occurring in July. The inoculation of these enteric pathogens is not unique to untreated water and are often traced to fecal contamination. Common sources are other swimmers (especially those under age 5), storm water runoff, flooding, sewage overflows, septic systems, boating waste and animal waste at or near the water source.

Other etiologies are more unique to untreated water. Avian schistosomes carried in most cases by birds cause cercarial dermatitis commonly known as swimmers itch. Naegleria fowleri, causes amebic meningoencephalitis after water containing the ameba enters the body through the nose and travels to the brain. This infection is usually fatal and is typically seen in persons who swim or dive in warm untreated fresh water. Many of these pathogens associated with illness are considered to be chlorine-susceptible and for this reason are rarely associated with outbreaks related to treated recreational water such as swimming pools.

Algal toxins produced by harmful algal blooms in fresh and saltwater can cause a range of illnesses ranging from skin or eye irritation to respiratory, gastrointestinal or neurologic symptoms depending on the type of toxin.

Per the CDC swimmers and parents of young swimmers are well advised to stay apprised of local swim advisories, and avoid swimming in discolored, smelly, foamy or scummy water. Additionally, swimmers should avoid or at least limit water entering the nose when swimming in freshwater.

Outbreaks caused by waterborne pathogens continue to make news and attract attention from local and state health officials. When these infections cause serious injury and death, lawsuits often follow. While there are far less water quality standards associated with untreated natural water sources such as lakes and beaches, any owner or manager of an untreated recreational water facility open for swimming or other exposure to untreated water, should be aware of and monitor conditions that increase the risk of a potential outbreak. This might include providing adequate and well stocked hygiene facilities, appropriate water testing and related record keeping, avoiding overcrowding, and prohibiting swimming soon after heavy rains or flooding, bird infestation or unusual algal growth.

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