February 2000
PHILADELPHIA - A study of the first recognized major outbreak of Shiga toxin-producing Escherichia coli (STEC) O111:H8 infections in North America confirms that the disease causes severe illness in otherwise healthy individuals.
Details of the outbreak, which occurred at a three-day cheerleading camp at the University of North Texas in Denton in June 1999, were presented here at the 37th Annual Meeting of the Infectious Diseases Society of America.
"STEC infections are estimated to cause more than 110,000 illnesses annually in the United States," said John T. Brooks, MD, epidemic intelligence service officer with the Centers for Disease Control and Prevention. "Up to 50% of these infections may be due to serotypes other than O157:H7."
In addition, about 85% of E. coli O157:H7 infections result from the consumption of contaminated foods, and most of the remainder from exposure to contaminated water. However, "sources for non-O157 STEC have not been well characterized, primarily because few outbreaks have been identified," he said.
![[bar]](/art/gradred.gif){kind=small}
The investigators conducted a cohort study of camp attendees, performed an environmental investigation of the dormitory cafeteria and cultured stool specimens. The teaching staff and campers younger than age 12 were excluded from the cohort. Illness was defined as either diarrhea (three or more bowel movements in 24 hours) with abdominal cramping, or bloody diarrhea occurring within 14 days after arriving at the camp. Overall, 80% (521 of 650) of the campers were interviewed, and of those 11% (58) met the case definition for illness.
"Questionnaires focused on food and beverage consumed during the camp. Most people ate all their meals at the university cafeteria," Brooks said.
In total, 95% of ill people were female (median age 16). Most illness began two days after camp began. Among ill persons, 62% reported nausea, 56% headache, 38% vomiting, 37% bloody diarrhea and 29% fever. The median of maximum number of stools in any 24-hour period was five, and the median duration of illness was five days (range one to 37 days). In addition, 7% of ill campers were hospitalized. "Two women were hospitalized with hemolytic uremic syndrome (HUS) and two others underwent appendectomies," Brooks said. There were no reported deaths.
Multivariate analysis implicated two independent exposures: using ice from open buckets in the dormitory foyer and eating from the salad bar in the dormitory cafeteria.
"We identified 21 exposures that were significantly associated with risk of developing illness," Brooks said. "These exposures included 18 food items from among 202 foods and beverages served at meals throughout the three days at camp."
Dinner on the first day of camp was also a risk factor, as was the consummation of ice from large, trash can-style barrels that the camp provided outside the dormitory for filling water bottles. "Campers dipped their hands into this ice with their water bottles and occasionally submerged their hands and arms to cool off," Brooks said.
The investigators were unable to determine the ultimate source of the E. coli O111 contamination for the outbreak. "Samples of the implicated food items and ice actually served during the cheerleading camp were no longer available for testing at the time of our investigation," Brooks said. "Although both the salad bar items and the barrels of ice were prepared in the same kitchen, once they left that kitchen, both were self-served and thus open to outside contamination. Contamination may, therefore, have occurred before, during or after the items were prepared or served."
Stool cultures for STEC were obtained from eight ill camper attendees. Two of these cultures yielded STEC O111:H8. "Both were sorbitol-positive, had detectable Shiga toxin by enzyme immunoassay (EIA), and contained gene sequences for Shiga toxins 1 and 2 by polymerase chain reaction (PCR)." Shiga toxin was also detected in a third culture-negative specimen.
"The true burden of disease from E. coli O111:H8 is unknown," Brooks said. "Few clinical laboratories routinely test suspect stool specimens for this and other non-O157 STEC," despite that between 1983 and 1998, E. coli O111 was the second most common non-O157 STEC that was serotyped at the CDC. E. coli O111 has also been isolated worldwide. An Australian outbreak in 1995 that was linked to dry sausage resulted in 24 cases of HUS and one death.
"Although other large outbreaks have occurred in Europe and Japan, the source of infection could not be determined," Brooks said.
To facilitate more rapid diagnosis of STEC infections, and to measure the burden of disease caused by these pathogens, Brooks and his colleagues recommend that clinicians (especially those likely to encounter STEC-related illness) inform health departments about clusters of disease that are consistent with STEC infection.
"Clinical laboratories should also screen stools of anyone with bloody diarrhea or HUS for STEC, using commercially available kits for the detection of Shiga toxin," Brooks said. Furthermore, "STEC isolated from Shiga-toxin positive stools should be referred to health state laboratories for serotyping." Finally, "isolation of STEC by state public health laboratories should be made a reportable disease."
For more information:
- Brooks JT, Bergmire-Sweat D, et al. Outbreak of Shiga-toxin producing Escherichia coli O111:H8 infections among attendees of a cheerleading camp. Session 727. Presented at the 37th Annual Meeting of the Infectious Diseases Society of America. Nov. 18-21, 1999. Philadelphia.
You can
express your views on this article, or other relevant themes, in the
Infectious Diseases in Children
Specialty Forums.