At least seven children are sick with E. Coli infections in a new outbreak involving an unknown source, according to an outbreak announcement by Washington State health officials.

All of the sick children are younger than 14, with three of them younger than five years old.

“Our investigation is ongoing, and we have not identified any foods, restaurants, or other sources in common among all cases. It is not yet known whether these cases share the same source or not,” officials reported in the announcement.

The children became ill between April 22 and May 1. Six of the seven children have been so sick they had to be admitted to hospitals. One of the sick children is confirmed as having developed a life-threatening kidney complication called hemolytic uremic syndrome (HUS) and is recovering. A second child is suspected to have HUS.

Six of the patients have preliminary testing indicating infections with E. coli O157 via PCR, and the seventh case has a positive EIA test for STEC, according to the announcement.

Further testing to confirm the strain and do genetic fingerprinting — whole genome sequencing or WGS — is underway at the Washington State Public Health Laboratory. The WGS results will help determine whether the patients were infected with the same strain of STEC.

“Public Health is conducting interviews with cases and their parents/guardians to help identify any common exposures. We are also working with the Washington State Department of Health to complete further testing and to help identify possible related cases in other counties,” King County officials reported.