MAQUOKETA — Health officials in eastern Iowa are looking for the source of an E. coli outbreak that has sickened several children in Maquoketa.

At least three children from Maquoketa are being treated at an Iowa City hospital after developing hemolytic uremic syndrome, a serious complication caused by a toxin-producing E. coli strain, the Telegraph Herald reported.

Doctors say the E. coli strain can cause diarrhea, stomach cramps and vomiting. HUS symptoms include dark-colored urine, increased fever, abdominal pain and headache and can affect kidney function.

The Jackson County Health Department is working to determine what might have caused the outbreak. Community Health Manager Michele Cullen said the process involves contact tracing, but a source has not been identified.