CDC report finds possible source for deadly 2022 Legionnaires’ disease outbreak in Napa

An outbreak of Legionnaires’ disease in downtown Napa that killed one person and hospitalized 16 others in 2022 has been linked to a cooling tower at an unspecified facility, according to a recent report.

A report from the U.S. Centers for Disease Control and Prevention that examined the disease outbreak that occurred from July to August 2022 contained new information about its possible origin and plans for remediation.

The report found that the identification of a specific strain of the disease in two patient specimens and at a cooling tower at a location referred to as “Facility A” supported a potential link between the facility and the outbreak.

A cooling tower is designed to remove heat from a building or facility by spraying water down through the tower to exchange heat into the inside of the building.

A clogged pipe that led to the chemical feed system at the facility impeded the controller’s ability to detect water flow, resulting in low or no injection of biocide — or disinfectant — into the tower, according to the report.

Maintenance records indicated the clog was detected in early July, the report says, at about the same time of several cases of exposure. The clog was resolved in early August.

While no precise location was given for “Facility A,” the CDC report places it on a map of Napa at the location of Embassy Suites by Hilton Napa Valley on California Boulevard. Napa County’s Health and Human Services previously said they detected Legionella bacterium in samples from a rooftop cooling tower there during the outbreak.

The Legionella bacteria that causes the disease are typically found in water, and the disease is contracted by inhaling small droplets of water or mist containing the bacteria. Legionnaires' disease is not transmitted from person to person.

Common sources of Legionella bacteria include cooling towers, hot tubs, plumbing systems, and air-conditioning systems. Symptoms of Legionnaires' disease can include high fever, cough, shortness of breath, muscle aches and headaches. It can be a serious illness, especially for individuals with weakened immune systems or underlying health conditions.

The report goes on to say that no cases of Legionnaires’ were detected among occupants of “Facility A.”

Given that studies show cooling towers can spread the Legionella bacterium over a wide geographic area, “this investigation further highlights the risks cooling towers can pose for susceptible persons in surrounding neighborhoods,” according to the report.

Cooling towers that aren’t properly maintained are associated with increased risk of bacteria, the report says.

A complaint filed Feb. 8, 2023, in Napa County Superiour Court by Southern California-based Riley Ersoff law firm on behalf of Calistoga resident Jason Groshart names Hilton Franchise Holding LLC, Embassy Suites Management LLC, Mani NVR Napa LLC, Chem-Aqua Inc. and Homeyer Consulting Services Inc. as defendants. All have been involved in some way with planning or maintaining the hotel’s water systems, according to the complaint.

A representative of Embassy Suites previously said the hotel did not comment on active litigation. Court proceedings in the matter are still ongoing.

The CDC’s report concluded that the response to the outbreak demonstrated the need to swiftly identify and mitigate sources of infection to stop transmission. That requires collaboration, according to the report, and includes public health agencies building close relationships with local businesses. In doing so the agencies can provide guidance on operation and maintenance of water systems.

“The investigation response to this community outbreak illustrates the importance of interdisciplinary collaboration by public health agencies, laboratory support, timely communication with the public, and cooperation of managers of potentially implicated water systems,” the report says.

The investigation kicked off after Napa County Public Health received three reports of positive tests for the disease on July 11 and 12, 2022, the report says. By July 21, six cases had been confirmed among Napa County residents, which compares to an average of one or two cases a year.

An environmental health investigation proceeded to identify possible exposure sources within a 1-mile high-risk zone, drawn around a cluster of patients’ residences. The public health agencies then mapped out a total of nine potential sources, including seven cooling towers, a decorative fountain and a produce mister.

“Visual inspection, review of records, and sampling of devices within the high-risk zone revealed a lack of maintenance at most cooling towers,” the report says. “Many had low or no detectable chlorine at the time of sampling, because of lack of routine biocide application, improper distribution methods, or other problems with the system.”

The five facilities that tested positive for Legionella were notified to remediate their cooling towers, the report says. One required a legal order to shut down a cooling tower because they failed to respond, according to the report.

The last case was detected Aug. 15, 2022, and facilities with cooling towers outside the high-risk area were told about the outbreak, along with best practices for cooling tower maintenance.

“A coordinated public health response was critical to the investigation of and response to this outbreak,” the report says.

You can reach Staff Writer Edward Booth at 707-521-5281 or edward.booth@pressdemocrat.com.