Surveillance for waterborne disease outbreaks--United States, 1991-1992.

PROBLEM/CONDITION: Since 1971, CDC and the U.S. Environmental Protection Agency have maintained a collaborative surveillance program for collection and periodic reporting of data on the occurrence and causes of waterborne disease outbreaks.

REPORTING PERIOD COVERED

January 1991 through December 1992.

DESCRIPTION OF SYSTEM

The surveillance system includes data about outbreaks associated with water intended for drinking and also about those associated with recreational water. State and local public health departments are the agencies with primary responsibility for the detection and investigation of outbreaks. State and territorial health departments report these outbreaks to CDC on a standard form.

RESULTS

For the 2-year period 1991-1992, 17 states and territories reported 34 outbreaks associated with water intended for drinking. The outbreaks caused an estimated 17,464 persons to become ill. A protozoal parasite (Giardia lamblia or Cryptosporidium) was identified as the etiologic agent for seven of the 11 outbreaks for which an agent was determined. Five (71%) of the outbreaks caused by protozoa were associated with a surface-influenced groundwater source. One outbreak of cryptosporidiosis was associated with filtered and chlorinated surface water. Shigella sonnei and hepatitis A virus were implicated in one outbreak each; both were linked to consumption of contaminated well water. Two outbreaks due to acute chemical poisoning were reported; one had an associated fatality. No etiology was established for 23 (68%) of the 34 outbreaks, including the largest one reported during this period, in which an estimated 9,847 persons using a filtered surface water supply developed gastroenteritis. Most (76%) of the 34 outbreaks were associated with a well water source. Twenty-one states reported 39 outbreaks associated with recreational water, in which an estimated 1,825 persons became ill. The most frequently reported illness was hot tub- or whirlpool-associated Pseudomonas dermatitis (12 outbreaks). Of 11 outbreaks of swimming-associated gastroenteritis, six were caused by Giardia or Cryptosporidium, including three outbreaks associated with chlorinated, filtered pool water. The first reported outbreak of Escherichia coli O157:H7 infection associated with recreational exposure occurred during this period. Primary amebic meningoencephalitis, caused by Naegleria fowleri infection, resulted in six deaths.

INTERPRETATION

The number of waterborne disease outbreaks reported per year has not changed substantially in the past 5 years. However, etiologic agents only recently associated with waterborne disease, such as E. coli O157:H7 and Cryptosporidium, are being reported more frequently and from new settings. Water quality data for outbreaks during the period 1991-1992 indicate that available water disinfection technology is not always in place or used reliably.(ABSTRACT TRUNCATED AT 400 WORDS)