Fourteen of those cases are in Chicago and one is in DuPage County.
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What to know after monkeypox case confirmed in US
The health commissioner in Gary also confirmed the city's first case of monkeypox. It's one of two cases that have been identified in Indiana.
As of June 17, the CDC has confirmed a total of 113 monkeypox cases nationwide.
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Doctors say monkeypox is generally spread by skin-to-skin contact, though it can also be passed through contaminated clothing or bedding. And while it can make patients very sick, it is not usually fatal. Symptoms include rashes, sores and lesions that often look severe, as well as fever and muscle aches.
The Chicago Department of Public Health said individuals attending festivals or other summer events should consider how much close, personal, skin-to-skin contact is likely to occur at the events they plan to attend.