According to the St. Louis Post-Dispatch, Five people have become ill with E. coli after visiting Grant’s Farm since late May, the Missouri Department of Health and Senior Services said Friday. The DHSS, along with the state and federal departments of agriculture and St. Louis area health agencies, is investigating what specifically led to the Shiga toxin-producing E. coli, or STEC.

Shiga toxin is harmful to humans. Symptoms can begin one to 10 days after exposure and can include severe stomach cramps, bloody diarrhea, vomiting and sometimes a low fever. Most people get better in about a week, according to the DHSS, but some infections can be severe or even life-threatening.

Grant’s Farm is participating in the investigation and is allowing investigators to take samples from the animals. Grant’s Farm already takes part in routine visits from state inspectors that provide oversight for the health of all the animals in the park, according to a DHSS statement.

While the investigation is taking place, the health department’s preliminary recommendation to Grant’s Farm is to remind patrons of the importance of washing their hands after having direct contact with animals.

“At Grant’s Farm, the safety of our patrons, our employees, and our animal population is our highest priority,” a Grant’s Farm official said in a statement. “Out of an abundance of caution, we will also be taking further safety measures, including the addition of several more hand-washing/antibacterial stations, and increased signage to remind our visitors of the importance of proper hygiene after coming into contact with the animals.”

Five to 10% of those infected with STEC can develop a serious kidney condition called hemolytic uremic syndrome, which requires hospitalization and can be fatal. Antibiotic treatment of STEC might increase a person’s risk for developing the syndrome and is not recommended, according to the DHSS.