CDC notes 72% rise in water-related outbreaks

Sep 23, 2011 (CIDRAP News) – Outbreaks linked to both recreational water and drinking water have increased substantially, according to two reports from the US Centers for Disease Control and Prevention (CDC), which said that Cryptosporidium contamination and groundwater problems pose special challenges.

The reports contain 2007 and 2008 data from waterborne illness surveillance collected by the CDC, the Environmental Protection Agency (EPA), and the Council of State and Territorial Epidemiologists (CSTE). The reports, one on recreational water and one focusing mainly on drinking water, were published today as Morbidity and Mortality Weekly Report (MMWR) surveillance summaries.

Snapshot of recreational water outbreaks
In 2007 and 2008, 134 outbreaks linked to recreational water were reported, up from 78 in the previous 2-year period—a nearly 72% increase. The CDC said in the first report that this is the most outbreaks ever reported during a 2-year period.

Outbreaks frequently involved treated water and resulted in acute gastrointestinal illnesses.

Reported from 38 states and Puerto Rico, they occurred in all months of the year, but more than half (61%) occurred during summer months. Recreational waterborne outbreaks resulted in at least 13,996 illnesses.

Parasites were the top cause of these outbreaks, led by Cryptosporidium, which was responsible for nearly 83% of infections involving gastrointestinal symptoms. The CDC said Cryptosporidium outbreaks typically started with a focal outbreak that spread to other recreational water venues.

Eighteen recreational water outbreaks were caused by bacteria, five were linked to viruses (all norovirus), and nine were linked to toxins such as chlorine gas.

Twenty-five states reported a total of 236 individual vibriosis cases, which represented about 20% of such cases reported for the 2 years. Eight individual cases of Naegleria fowleri were reported, all fatal and all occurring in warm, untreated freshwater in southern states.

In its analysis of the findings, the CDC attributed the rise in recreational-related waterborne illness outbreaks to changes in reporting and the emergence of Cryptosporidium as the single most important etiologic agent. Among outbreaks in the study, 60 were caused by the pathogen, only two of which involved untreated water.

The central role Cryptosporidium played in the outbreaks may relate to its chlorine tolerance, the CDC said, noting that it can survive in properly treated water for more than 10 days and has a long incubation period, about 7 days.

Modifying swimming behavior, such as bathing with soap before entering the water, is a key component of reducing the number of Cryptosporidium outbreaks, the CDC said. Other types of disinfection systems, such as ultraviolet and ozone, can inactivate the parasite and are available for treating recreational water.

Stronger outbreak control plans can also reduce the impact of outbreaks. The CDC highlighted public awareness campaigns in Salt Lake County, Utah, and Idaho launched before the 2008 swim season that focused on preventing Cryptosporidium outbreaks. For that year, Utah reported no such outbreaks, and Idaho reported only one that involved two cases.

The CDC report also noted the challenges of controlling pathogens in other settings, such as spas, interactive fountains, fill-and-drain pools, and temporary water slides.

Drinking water outbreak patterns
Outbreaks involving drinking water rose 80% over the previous 2 years, according to the second CDC report, which put the total at 36 outbreaks from 23 states and Puerto Rico. Those outbreaks caused 4,128 illnesses and 3 deaths. More than half (21) were linked to bacterial contamination, and 13 were associated with groundwater.

Drinking water outbreaks predominately occurred in the spring and fall. Gastrointestinal illnesses led the outbreak symptom list.

Twelve outbreaks were related to Legionella contamination, of which 5 occurred in hospitals and 3 in nursing homes.

In its discussion of the drinking water outbreaks, the CDC said the large role of untreated or inadequately treated groundwater suggests that more efforts are needed to monitor and protect it from contamination. It suggested that full implementation of 2006 groundwater legislation over the next few years is expected to reduce the number of related outbreaks, similar to what occurred after surface water regulations took effect.

Though the findings pointed to the need for better control and elimination of Legionella, the CDC said more than half of the outbreaks were from one state (New York), which could stem from differences in outbreak detection and reporting.

Hlavsa MC, Roberts VA, Anderson AR, et al. Surveillance for waterborne disease outbreaks and other health events associated with recreational water--United States, 2007-2008 MMWR 2011 Sep 23;60(ss12):1-32 [Full text]

Brunkard JM, Ailes E, Roberts VA, et al. Surveillance for waterborne disease outbreaks associated with drinking water--United States, 2007-2008. MMWR 2011 Sep 23;60(ss12):38-68 [Full text]

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