Nine children were hospitalized, two in critical condition, with a life-threatening kidney ailment after visiting petting zoos in Florida. The total increased after two more children were diagnosed on Thursday, officials said.

There were fears the number of children suffering from the rare disease — hemolytic uremic syndrome (search), or HUS — would continue to grow. HUS, which generally affects children up to 10 years old, attacks and shuts down the liver and also disrupts blood circulation, which can lead to multiple organ failure.

The afflicted children had all touched animals at fairs, including the Central Florida Fair (search) in Orlando and the Florida Strawberry Festival (search) in Plant City. Officials said the children may have been exposed to E. Coli bacteria after petting the animals and then putting their fingers in their mouths, while eating, for example.

In addition to those hospitalized, two children and an adult showing symptoms of HUS were under observation, said Dr. Mehul Dixit, who is treating some of the children at Florida Hospital Orlando (search).

Florida Department of Health officials advised people to watch their children for symptoms including bloody diarrhea, lethargy, anemia and decreased urine output. Doctors warned that HUS can spread quickly and easily.

Officials also suggested that anyone visiting a petting zoo wash their hands with hot, soapy water after touching animals. A change of clothing was also suggested, and dirty clothing should not be worn until it was washed and soaked in hot water.

Florida Agriculture Commissioner Charles Bronson said state veterinarians are tracking down the animals so they can be inspected to determine what infections, if any, might have been transmitted.

Veterinarians also are reviewing sanitary measures at the petting zoos.

The Associated Press contributed to this report.