2002 Lane County Fair O157

OUTBREAK SUMMARY
The 2002 Lane County Fair was the site of the largest outbreak of E. coli O157 in state history with 72 confirmed cases, 9 presumptive cases and 11 cases with hemolytic uremic syndrome (HUS). Oregon epidemiologists discovered that an animal exhibit, not food vendors, was the source of the outbreak. Individuals who visited goats and sheep in the small animal exhibit were exposed to E. coli O157 through touching the ground or dirt in the animal area. Although five handwashing stations were available, many visitors confessed they did not wash their hands after visiting the small animal exhibit. The facility was cleaned before public health investigators arrived; but culture of environmental samples from the ceiling of the exhibition hall ten days after the fair ended yielded E. coli O157, suggesting spread on dust particles.

DETAILS:
Background
On August 21, 2002, a Eugene-based pediatrician contacted the Lane County Health Department (LCHD) to report one child with E. coli O157 infection and another with bloody diarrhea. She also alerted other physicians about the illnesses and asked them to report any additional diarrheal illnesses. Two additional children with culture-confirmed E. coli O157 infections were reported to LCHD officials within a day. These were the first confirmed O157 cases reported to LCHD in more than a year.

Oregon epidemiologists began investigating to determine the source of the outbreak; preliminary interviews suggested a connection to the Lane County Fair. Although food is often the vehicle for E. coli O157, epidemiologists began suspecting the outbreak started in the animal barns, specifically where small animals such as pigs, sheep and goats were kept. E. coli O157 may be found on animals, on the ground, and even on fence rails in animal exhibit areas. Epidemiologists interviewed nearly 200 sick and healthy fairgoers and effectively ruled out food or water as sources of the outbreak.

Methods
Epidemiologists engaged in active case-finding through outreach to clinicians, labs, and other health departments. Confirmed cases had E. coli O157 infections with matching pulse-field gel electrophoresis patterns; presumptive cases were fair attendees or person epidemiologically linked to confirmed cases who had bloody diarrhea or HUS. A case-control study was conducted using culture-confirmed, primary cases identified through routine surveillance. Controls were identified through credit card receipts of fair attendees and from a list of children who entered an art competition at the fair. Analysis was stratified by age.

Fair organizers identified more than 35 vendors that sold food or beverages at the fair. Epidemiologists developed a four-page questionnaire to query about potential food and animal exposures. Maps of fair venues showing all food concessions were developed and used with the questionnaire to collect accurate information from cases and controls about food consumptions and visiting animal exhibits. Swabs collected from the small animal exhibition hall by Dr. William Keene August 29, 2002 (10 days after the fair had ended, and after the barns had been cleaned), were cultured at the Oregon State Public Health Laboratory.

Results
Ultimately, 72 confirmed and 9 presumptive cases were identified. Forty seven (58%) were <5 years of age; 52 (64%) were female. Eighty visited a clinician, and 22 (27%) were hospitalized at least overnight. Thirty-five cases and 38 controls were interviewed for the case-control study. Cases were no more likely to eat food from concessionaires, and no single concessionaire was named by even a suggestive plurality of cases.

Illness was associated with visiting the small animal exhibition hall (odds ratio 7.6, 95% confidence interval 2.4-24). Only 31% of cases, and 36% of controls, reported having washed their hands after leaving the animal areas. Culture of environmental samples from the ceiling of the exhibition hall yielded E. coli O157.

Lessons Learned
This was the largest E. coli O157 outbreak in Oregon history. Although food is often implicated of E. coli O157, in this case exposure to an animal exhibit was proved to be the source. Handwashing after petting animals or visiting animal exhibits is key in preventing infection and illness. In this outbreak, the finding of E. coli O157 in the rafters of a building supports the idea that O157 can survive on dust particles for significant lengths of time.

Documents
Document 1: Questionnaire
Document 2: CD Summary: Hemorrhagic escherichiosis from a county fair

Media coverage
Media story 1: Fairgoer E. coli cases on the rise
Media story 2: More E. coli cases from county fair
Media story 3: Probe ties E. coli to sheep, goat barns
Media story 4: Aerosol Transmission Of E-Coli 0157 Suspected
Public Service Announcement: Oregon Public Health PSA