PROVO — A state laboratory that tested samples taken from a Payson dairy farm did not find traces of the bacteria that sickened as many as 43 Utah County residents over the past week.

Health officials, however, say the outbreak of the food-borne illness still could have originated at Woolsey's Dairy and urge the public to be careful when considering drinking unpasteurized milk.

"It's very possible that an earlier batch had been contaminated and all the traces worked their way out of the system," said Lance Madigan, Utah County Health Department spokesman.

A spokesman for the Utah Department of Agriculture and Food confirmed that the contamination could have happened at the dairy at an earlier date.

"We were testing to check the current batch of milk," said UDAF spokesman Larry Lewis. "This doesn't speak to the milk that may have contributed to the illness of these people, which would have been produced weeks before."

Utah County Health Department officials issued a health advisory Wednesday after receiving multiple reports of campylobacteriosis, a disease caused by ingesting bacteria commonly found in unpasteurized milk products and improperly prepared chicken.

A number of those infected said they had purchased raw milk products from Woolsey's Dairy, 2232 West S.R. 198, prompting the health advisory and testing.

The Utah County Health Department has received 43 reports of people exhibiting the symptoms of campylobacteriosis in the last week, Madigan said. The department usually sees three such cases per month.

Culture testing has confirmed the presence of bacteria in 20 of those individuals, 11 of whom said they had consumed raw milk from Woolsey Dairy, Madigan said.

Campylobacteriosis is a relatively benign infection; its main symptoms are diarrhea, cramping, abdominal pain and fever. Some more severe cases may cause nausea and vomiting as well.

Symptoms are manifest within one to 10 days after the bacteria are ingested.

Madigan said the health department investigates every reported case as a matter of procedure. Other tests, including a DNA test to see if the confirmed cases are from the same strain of bacteria, are still being conducted, and the outbreak could still be successfully traced back to its source, Madigan said.

He added that the current outbreak has most likely peaked.

"We suspect we'll start seeing (cases) drop off soon," Madigan said. "It does appear the current strain has run its course."

Dairy owner Lars Woolsey didn't immediately return phone messages Monday seeking comment.

Officials at the county health department and department of agriculture and food are emphasizing the potential dangers of consuming raw milk.

"Raw milk is not risk-free," Lewis said. "This test says (Woolsey Dairy) was doing everything right on that day, but raw milk is very volatile and consumers need to keep that in mind."