PHILADELPHIA (AP) — Philadelphia is reinstating its indoor mask mandate after reporting a sharp increase in coronavirus infections, the city’s top health official announced Monday.

Confirmed COVID-19 cases have risen more than 50% in 10 days, the threshold at which the city’s guidelines call for people to wear masks indoors, said Dr. Cheryl Bettigole, the health commissioner.

The city is reporting more than 140 cases per day, a fraction of what it saw at the height of the omicron surge, and hospitalizations remain low. But Bettigole said the recent increase in infections indicates the city might be at the beginning of a new wave, and city officials are seeking to stay ahead of it by requiring indoor masking.

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Health inspectors will start to enforce the mask mandate at city businesses starting April 18.