By Ethan Covey
A manufacturing facility in South Carolina has been identified as the source of a cluster of legionellosis cases that took place from August through November 2022.
The outbreak was notable for the severity of the illness. Among 34 cases of legionellosis identified during the epidemiological investigation, 15 hospitalizations and two deaths were reported (Emerg Infect Dis 2025;31[1]:41-49).
“To the best of my knowledge, this is the largest Legionella outbreak linked to an industrial facility in the U.S.,” said the lead author of the report, Hani M. Mohamed, MBBS, MS, a foodborne disease epidemiologist with the South Carolina Department of Health and Environmental Control (DHEC), in Columbia.
The DHEC Division of Acute Disease Epidemiology initially was alerted in September 2022 regarding three Legionella-positive tests among people who were hospitalized with pneumonia. All of the patients worked at the same manufacturing facility, located in Richland County, S.C.
An investigation revealed 34 people who met the case definition for legionellosis. Of these, 20 had probable Legionnaires’ disease, and four had probable Pontiac fever. The median age of the patients was 40 years, lower than the national median age of Legionnaires’ disease cases, which is 62 years.
Two unique equipment sources of Legionella bacteria were identified. Legionella pneumophila was isolated from three devices: two water jet cutters and one floor scrubber. L. pneumophila sequence type 36 was identified in environmental isolates and one patient specimen, indicating that those devices were the likely source of infection.
After receiving the initial Legionella sampling results, the company discontinued use of both water jet cutters and all floor scrubbers. The water jet cutters were returned to service in mid-November 2022, and the floor scrubbers were replaced with backup units.
“The investigation was initially challenging because a clear exposure pattern did not exist between worksites of ill workers, and the devices that aerosolize water,” Dr. Mohamed said. “However, this lack of a pattern suggested that the source had to be capable of causing widespread exposures.”
Dr. Mohamed noted that another challenge was associated with the remediation process.
“Remediation of the water jet cutter contamination was complicated by the absence of existing water management recommendations,” he told Infectious Disease Special Edition. “Because of vulnerable components in the devices, such as the cutting head that is susceptible to corrosion, chemicals added to the water reservoirs had the potential to damage the equipment.”
The authors noted that early reporting of the cluster and timely identification of the common occupational exposure among patients were key to limiting the duration of the outbreak, and information from the investigation will hopefully aid in preventing future outbreaks in manufacturing settings.
“Manufacturing facilities should consider maintaining updated Legionella water management programs that specify when, where and how control measures should be applied to prevent legionellosis cases and clusters, as new technology emerges,” Dr. Mohamed said. “Our experience highlights the need for public health authorities to consider nontypical sources of Legionella exposure when investigating legionellosis cases and clusters at manufacturing facilities.”
The sources reported no relevant financial disclosures.
