September 24, 2002
The E. coli bacteria that sickened 82 people at this summer's Lane County Fair may have spread through the air inside the goat and sheep expo hall, the outbreak's lead investigator said Monday.
"It's quite possible some people were exposed through airborne transmission," said Dr. William Keene, an epidemiologist with Oregon Health Services. "We don't know if it was a few or almost all of them."
Keene suspects that E. coli was in the air based on samples of dust and grime he took inside the barn after the outbreak.
He took 25 swabs from the floor, fencing stacked along the walls and spots up high in the barn. Three samples tested positive for the virulent E. coli O157:H7 strain, and all three were 15 feet to 18 feet off the ground, he said.
One sample was taken from atop some pipes; one from some rolled-up netting; and one from a fan housing.
"It indicates it blew up there," he said. "There weren't any animals up there."
Once airborne, the bacteria could settle on railings, animal fur, on human skin or in food. It's also possible people swallowed contaminated dust.
That means fairgoers wouldn't have had to touch an animal to get infected with E. coli, he said. It's likely some areas were more contaminated than others.
Last month's E. coli outbreak was the biggest in state history, and the latest in a series of E. coli outbreaks at county fairs and petting zoos around the country in the past three years.
Of the 74 confirmed and eight presumed cases here, nearly two-thirds involved children under 6 years old. Twelve children went to hospitals in Portland for treatment of hemolytic uremic syndrome, or HUS, a potentially deadly complication of E. coli infection that can cause the kidneys to fail.
One child, 23-month-old Carson Walter of Eugene, spent a month at Doernbecher Children's Hospital before coming home on Friday.
If Keene's theory is correct, it marks the second time in a year that airborne E. coli has infected people at county fairs.
Last year, E. coli sickened 23 people at the Lorain County Fair in Ohio, and public health investigators traced the outbreak to an animal show barn where a teen dance was held.
Investigators swabbed the barn and found E. coli in the rafters, on the bleachers and walls and in sawdust on the floor. Investigators suspect that the E. coli bacteria became airborne in the dust, then landed in the food and drinks of fairgoers in the barn.
Investigating an infectious disease outbreak has been compared to trying to assemble a jigsaw puzzle without knowing what the picture looks like. For Keene, being aware of the Ohio outbreak gave him a glimpse of the picture.
"If this were the first time (airborne transmission) was suggested, we'd be a little more cautious suggesting it was possible," he said. "You learn from what other people do."
Keene doesn't know what to tell county fair operators about how to protect people from airborne E. coli, but he'll consult with public health officials around the country to determine reasonable safeguards for fairs.
"We're just scratching our heads, trying to figure out what's both reasonable and reasonably effective," he said.
While hand washing remains the single most effective strategy for preventing the spread of disease, it appeared to be of little help in preventing the Lane County outbreak.
The percentage of sick people who washed their hands after leaving the animal barns - 31 percent - was only slightly lower than the percentage of healthy people who washed their hands - 36 percent.
The overall risk remains quite low at the fair, he said. Only 82 of the roughly 50,000 people who went through the small animal expo hall got sick, he said. "It's a low number," he said.
Still, finding E. coli lurking 15 feet off the ground inside the barn raises questions that have no clear answers. Keene hopes that the two suspected airborne outbreaks of E. coli will spur researchers to study the issue.
Among the questions:
How long had the E. coli been up in the rafters and pipes, and did it get there before the fair, during the fair, or after the fair?
Scientists know the bacteria can survive in the environment for weeks and even months, Keene said. It's less clear how long it presents a threat.
Warren Wong, the fair's managing director, said he didn't think the E. coli got up in the rafters during the fair. "I couldn't imagine manure drying so quickly it would get up in the dust," he said.
While cows, a common E. coli carrier, were in the building the month before the fair, Keene suspects the bacteria were blown up there during the fair.
"I lean pretty heavily on the fact that people did not get sick on the first two days of the fair," he said. "It's possible something happened (during the fair) to suddenly dislodge a bunch of grime on the pipes. It's much easier to imagine something started happening when the animals start pooping."
It's possible that a goat or sheep pellet could dry out in the heat and get ground up when people and animals walked on it, then get kicked up with dust into the air, Keene said.
"None of the people I talked to thought it was terribly dusty in there," he said. "That's a little unsatisfying."
Fans circulating air in the barn could have spread the bug. In addition to permanent exhaust fans at the roof's edge, some exhibitors brought their own fans, which they placed in the pens to cool their animals, said Rich Diamond, the fair's operations manager.
Wong said fair crews hosed down the inside of the barn after this year's fair, though they can't shoot water inside the heating unit or onto light fixtures.
Wong said he's looking into ways to sanitize the inside of the building, either with steam or a chlorine solution.
The expo hall should be safe now for other activities, Keene said. Any bacteria that were in the air would fall to the ground quickly, he said.
"I believe that finding the organism in the building does not necessarily translate to any significant risk to people going in there now," he said. "Stuff that blows around and sits in rafters doesn't necessarily come down and bite people."
OTHER CASES OF E. COLI
Since 1999, at least eight E. coli outbreaks have occurred at county fairs and dairy farms where visitors had contact with animals.
- August 1999: Washington County Fair, N.Y.: Public health officials confirmed 127 cases of E. coli O157:H7 and 45 cases of campylobacteriosis, another bacterial disease that causes diarrhea; about 800 people reported symptoms. Seventy-one people were hospitalized, 14 developed hemolytic uremic syndrome, or HUS. Two people died: a 3-year-old girl and a 79-year-old woman. The outbreak was traced to a well contaminated by a dormitory septic system and possibly by manure runoff from a cattle barn.
- Centers for Disease Control and Prevention