Five children have contracted a life-threatening kidney infection, which health officials said may be the result of a rare infection picked up at petting zoos.

Three children remained in critical condition Wednesday, while another was in stable condition. The condition of the fifth child was not immediately known.

Four of the children were hospitalized after visiting the Central Florida Fair (search), which ended March 13 in Orlando. A fifth child was stricken after going to a petting zoo at the Florida Strawberry Festival in Plant City, which ended the same day.

The potentially dangerous kidney condition — hemolytic uremic syndrome (search), or HUS — is a rare complication arising from an infection most commonly associated with E. coli, a bacterium found in undercooked beef or contaminated food.

The children might have been exposed to the bacteria through the animals' feces, officials said.

Bill Toth, a spokesman for the Orange County Health Department, said not all the children showed signs of E. coli (search) exposure, and investigators were running additional tests.

Officials said three of the children tested positive for a different bacterium — Staphylococcus aureus — that can sometimes lead to the kidney problem.

Central Florida Fair manager Charles Price said petting zoo exhibits are inspected by health officials and veterinarians.

"We have hand-washing stations everywhere," he said. "A fair today is not like it was 15 years ago. We are under extreme scrutiny."

An official with the Strawberry Festival wouldn't comment.

Officials were looking into whether a sixth child treated for the same ailment about four weeks ago also came into contact with petting zoo animals.

Last fall, 15 children developed the life-threatening kidney ailment in North Carolina, and a petting zoo exhibit at the state fair in October was determined to be the likely source. In all, 108 people, more than half of them small children, were affected by E. coli traced to the fair, though most had far milder symptoms than the 15.

About 73,000 cases of E. coli infection are reported in the United States each year; an average of 61 prove fatal.