(CNN) A pediatric healthcare worker in Michigan was ill with tuberculosis and didn't know it while working in several locations over nine months, the state's health department said.

The worker was recently diagnosed with pulmonary tuberculosis, and the department is working with medical groups to find out whether patients who were in close contact with the worker were exposed, the Michigan Department of Health and Human Services said in a release.

The worker, who is receiving treatment, was at the locations between April 1, 2019, and January 9.

All associates and providers at the pediatric practice have been tested and do not have active TB disease, according to the health department.

"TB is a treatable bacterial disease that is spread through the air from one person to another," said Dr. Joneigh Khaldun, chief medical executive and chief deputy for health for the department, in the release. "While the infection can be serious, not everyone who is exposed to TB will be infected, and many people who are infected never develop symptoms."

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