(KRON) — Contra Costa County health officials said water samples collected from a Richmond day spa’s hot tub contained high levels of legionella bacteria, making it the likely source of two Legionnaires’ disease deaths.

Contra Costa Health began investigating Zen Day Spa on August 4, less than 24 hours after two patients died in hospitals. Both patients had visited the spa before becoming ill with Legionnaires’ disease.

County health officials discovered that the spa, located at 12230 San Pablo Avenue, was operating without a health permit and had an illegal hot tub. The hot tub at Zen Day Spa was designed for private — not commercial — use.

“CCH collected water and swab samples and, while still awaiting final reports from the lab, initial results show high concentrations of legionella bacteria,” health officials announced Monday.

CCH contacted more than 30 recent customers of Zen Day Spa as part of its investigation, as well as multiple customers who became sick with Legionnaires’ disease.

In addition to the two people who died, CCH identified four more customers whom investigators suspect had Legionnaires’ disease.

While legionella bacteria naturally live in fresh water, health concerns can arise in hot tubs and pools where the bacteria can grow if the water is not maintained properly. People can become infected after breathing mist containing the bacteria. Symptoms include shortness of breath, muscle aches and fever. The disease can cause serious serious cases of pneumonia, health officials said.

The business voluntarily closed on August 5. On Monday, the county health department issued an abatement order declaring the business a “public nuisance” and ordered the spa to remove its hot tube. The business cannot reopen until it is re-inspected by CCH.

Deputy health officer Dr. Meera Sreenivasan said, because the spa has been closed since August 5, health officials do not anticipate new cases arising. The disease does not spread from person to person, Sreenivasan said.

The public can use CCH’s swimming pool and spa inspection database to see recent inspection results of public pools and hot tubs in Contra Costa County.