The festival took place between Aug. 6 and 8.
"We are interested in learning more about COVID-19 transmission related to large public gatherings where people congregate in indoor and outdoor spaces," city officials said. "Learning more about these events will help us develop recommendations and guidance so that these events can continue to be held safely in the future."
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"Several" cases were identified during the investigation among Chicago, non-Chicago and out-of-state residents, health officials said.
Anyone who attended Market Days and later tested positive for COVID-19 can self-report their case directly to CDPH at https://redcap.link/reportmarketdays.