Mendocino County public health officials reported Thursday that tests at a Ukiah motel for the bacteria that causes Legionnaires’ disease produced inconclusive results.

The Discovery Inn was the only common factor between three Mendocino County residents who recently became ill and were hospitalized for Legionnaires’ disease. The three individuals, who all stayed at the motel between June and August, have been treated and released from the hospital.

To date, there are no additional confirmed cases, officials said.

Legionnaires’ disease is a severe form of pneumonia that is transmitted by inhaling airborne water droplets containing the bacterium known as legionella; it is not spread from person to person. The illness often is cured through the prompt use of antibiotics but can be fatal if left untreated.

Investigators tested the motel’s water systems but the results were inconclusive. County public and environmental health officials continue to investigate for other possible common factors. The county said the Discovery Inn has contracted a company specializing in regulated public water system safety to disinfect water lines and fountains as a precautionary step.

According to the federal Centers for Disease Control and Prevention, legionella bacteria grow best in warm water, such as that found in hot tubs, cooling towers, large plumbing systems and decorative fountains.

An estimated 8,000 to 18,000 people in the U.S. are hospitalized with Legionnaires’ disease each year, according to the CDC. But only about 3,000 cases are reported to the agency annually.

Read all of the PD's fire coverage here