PROVIDENCE, Rhode Island — Public health officials are investigating a rise in the number of cases of Legionnaires’ disease in Rhode Island, the state Department of Health said Monday.

There have been 30 cases reported since June 2, the agency said in an emailed statement. Of those, 28 people have required hospitalization. The state has had an average of 10 cases per month in June and July since 2014, the agency said.

No common source of exposure has been identified.

“This is of particular concern now as some buildings’ water systems have been offline for a prolonged period due to the COVID-19 pandemic and are just now returning to service.”

Legionella is especially a concern in buildings that primarily house people older than 65, buildings with multiple housing units and a centralized hot water system like hotels or high-rise apartment complexes.

Symptoms, which typically start two to 10 days after breathing in the bacteria, can include cough, shortness of breath, fever, muscle aches and headaches.

It can be treated with antibiotics, and most people who get it make a full recovery, but about 1 in 10 people who get the disease die, the department said.