Nov 26, 2003 (CIDRAP News) – A contaminated multipurpose building apparently was the source of Escherichia coli O157 exposure for at least 19 people who got sick after attending a county fair in Ohio in 2001, according to a study published this week.
Widespread contamination of surfaces in the building probably resulted from airborne spread of the pathogen from sawdust on the floor, according to the report in the Journal of the American Medical Association. People most likely became infected when they ate or drank after touching tainted surfaces or when airborne bacteria landed on their food or in their mouths, the report says.
E coli O157 usually spreads to people in contaminated food or water or through contact with farm animals or other sick people. The Ohio outbreak appears to be the first in which "both epidemiological and microbiological data implicate a contaminated building as the source of infection," says the report by a team of public health officials led by Jay K. Varma, MD, of the Centers for Disease Control and Prevention (CDC).
The investigators identified 23 people who experienced diarrhea within a week after attending the Lorain County Fair in August 2001 and who met other case criteria, such as laboratory-confirmed E coli O157. Six of these were hospitalized and two had hemolytic uremic syndrome (HUS), but all survived. For comparison purposes, the investigators found 53 age-matched people who had attended the fair but remained healthy afterward. The case-patients and controls filled out questionnaires about their clinical history and their activities at the fair.
Patients were more likely than controls to have visited the multipurpose building (19 of 23 versus 23 of 52; matched odds ratio [MOR], 21.4; 95% confidence interval [CI], 2.7 to 170.7). Among those who visited the building, illness was independently associated with attending a dance in the building (MOR, 7.5; 95% CI, 1.4 to 41.2), handling sawdust from the floor (MOR, 4.6; 95% CI, 1.1 to 20.0), and eating or drinking in the building (MOR, 4.5; 95% CI, 1.2 to 16.6). Eating a hamburger or dinking beverages made with fairgrounds water was not linked with illness.
The multipurpose building, a wooden structure with open rafters and bleachers surrounding a central show area, is used for exhibits, concerts, dances, and animal shows, the report says. The clay floor is covered with sawdust. The authors collected environmental samples in the building 6 weeks, 14 weeks, and 42 weeks after the fair and sent them to the CDC for culturing. Twenty-four of 54 specimens collected 6 weeks after the fair yielded Shiga toxin–producing E coli O157. Molecular fingerprinting (pulsed-field gel electrophoresis) of 12 of the 24 specimens showed they matched isolates from 10 patients.
Fourteen weeks after the fair, 8 of 16 samples from the building, including some from railings, bleachers, and rafters, still yielded Shiga toxin–producing E coli O157. At 42 weeks, the pathogen was still found in sawdust from the floor but not on other surfaces.
The authors speculate that the building first became contaminated when an infected cow or other animal shed E coli O157 by defecating on the floor. The pathogen survived and possibly multiplied in the sawdust, and sawdust may have become airborne during the dance or another large event, the report says. Some of those who attended the dance said the air was dusty.
"Individuals who touched contaminated surfaces in the building became infected when they ate or drank without adequately washing their hands," the authors suggest. "It is possible that some may have swallowed bacteria that landed directly into their mouths or onto their food or drink."
The authors recommend that fair managers and health officials warn the public that hazards in animal environments can persist for months after the animals have been removed. Frequent handwashing is known to reduce the risk of E coli O157 infection, but further research is needed to determine if this measure "is sufficient when environmental contamination is widespread and bacteria may be dispersed in the air," the report concludes.
Airborne spread of E coli has been cited as a possible factor in at least one other recent outbreak, in Lane County, Ore., in 2002. More than 80 cases occurred in people who visited a building housing sheep, goats, and other animals during a fair there, according to information on the Oregon Department of Human Services Web site. Although the exact route of transmission was never determined, "it was learned that at some point the pathogen became airborne in quantities sufficient to be recovered under the pavilion's roof weeks after the fair," the department reports.
Varma JK, Greene KD, Reller ME, et al. An outbreak of Escherichia coli O157 infection following exposure to a contaminated building. JAMA 2003;290(20):2709-12 [Abstract]