Dallas County Health and Human Services confirmed to FOX 4 that it is lab testing a cluster of E. coli cases caused by the shiga toxin-producing strain. The department said it is investigating whether the cases came from a petting zoo at the State Fair of Texas.

The department said the cases affect children of a range of ages and that interviews with those involved are ongoing. It does not currently classify the cases as an outbreak. At least two parents told FOX 4 their children are hospitalized in Dallas. Children's Medical Center Dallas said it has seen an uptick in cases.

According to the report, E. coli symptoms begin with bloody stools and vomiting, and people can be infected through contaminated food or water or from infected animals. Carla Garcia Carreno, medical director for infection prevention and control at Children's Health Plano, said young children often do not wash their hands or keep their hands away from their mouths.

The State Fair of Texas said it has not received official notification of the reports. It said it takes concerns about guest health and safety seriously and is prepared to work with public health authorities. The fair said it has health and safety precautions for its animal exhibits.