Epidemiologic Investigation

The South Carolina Department of Health and Environmental Control (DHEC) Division of Acute Disease Epidemiology (DADE) used the South Carolina electronic disease surveillance system to collect epidemiologic data for this study. We identified confirmed and suspected legionellosis cases on the basis of the 2020 Council of State and Territorial Epidemiologists case definitions (12).

During September 2022, DADE received reports of 3 Legionella-positive urinary antigen tests among patients hospitalized with pneumonia who all worked at the same manufacturing facility in Richland County, South Carolina. DADE informed company management about the cluster of legionellosis cases among facility employees and shared an employee awareness notification letter for distribution to employees. Company management informed employees of the legionellosis cluster and the DHEC investigation through both in-person meetings and virtual and electronic communications. DHEC released a statewide health advisory to healthcare providers that had specific recommendations and a reminder to report positive Legionella test results and legionellosis cases to DHEC. Because of the occupational setting of the cluster, DADE requested assistance with the epidemiologic investigation from subject matter experts from CDC, including those from the National Institute for Occupational Safety and Health.

Regional epidemiologists conducted telephone interviews of ill persons to collect epidemiologic data for the 14-day period before symptom onset. All patients linked to this cluster were interviewed by using a standardized epidemiologic questionnaire, which gathered demographic information, clinical manifestations, laboratory results, travel history, and potential exposure to high-risk settings and water sources. Patients were asked questions about job title, job description, job location, frequently visited areas aside from the assigned workplace, and visits to other potential exposure sites. Company management provided information about the building and the water distribution systems that included all water processing equipment. We considered the location’s potable water points of use as possible exposure sites, in addition to the water processing equipment. To estimate disease burden, we classified cases into the following 4 categories: confirmed Legionnaires’ disease, defined as a patient who was at the facility and had a clinically compatible case of severe pneumonia with confirmed laboratory evidence of Legionella infection and onset of illness on or after May 2022; probable Legionnaires’ disease, defined as a patient who was at the facility and had a clinically compatible case with no laboratory evidence of infection but with onset of illness on or after May 2022; confirmed Pontiac fever, defined as a patient who was at the facility and had a clinically compatible case of mild respiratory disease (no pneumonia) with confirmed laboratory evidence of Legionella infection and onset of illness on or after May 2022; and probable Pontiac fever, defined as a patient who was at the facility and had a clinically compatible case with no laboratory evidence of infection but with onset of illness on or after May 2022.

Case Finding

DADE asked the facility’s occupational health service to actively identify all persons who had new or recent (previous 3 months) self-reported lower respiratory symptoms or clinically diagnosed pneumonia. Those persons were encouraged to contact their primary care physicians for Legionella bacteria assessment by using both culture of lower respiratory secretions and a Legionella-specific urinary antigen test. In addition, the lead regional investigators (R.W., V.G.) reached out to symptomatic co-workers who were identified by patients with confirmed legionellosis or the employee health service. DADE also conducted a retrospective search of the South Carolina electronic surveillance system for all legionellosis patients who reported working at the same facility within the previous 12 months, in addition to looking for similar worksite exposures reported by patients living in other regions. The DHEC health advisory and employee communications letter promoted seeking early healthcare and made employees aware that they should be tested for Legionnaires’ disease if any respiratory symptoms developed.

Environmental Investigation and Sampling

Company management hired a Legionella consultant (M.G.) who collected preremediation and postremediation environmental samples and sent them to an Environmental Legionella Isolation Techniques Evaluation Program member laboratory. The laboratory conducted serial Legionella bacteria testing of potable and nonpotable water sources. In preremediation environmental samples, L. pneumophila and Legionella spp. were detected by using qualitative PCR. Results were reported as detected or not detected. Preremediation and postremediation environmental samples were also collected and tested by using traditional culture (spread plate); those results were reported as colony forming units per volume. The environmental samples were from traditional potential exposure sources, such as showerheads, sinks, and cooling towers, and multiple unique sources, such as floor scrubbers and water jet cutters.

Legionella Bacteria Environmental Risk Assessment

After DADE notified the company of the cluster, company management engaged a consultant with Legionella bacteria expertise. They used the CDC’s Legionella Environmental Assessment Form to collect information about the water supply, water system design, and potential sources of exposure (13). They then used that information to create a water use inventory with detailed information and descriptions for 42 devices, including plumbing and bathroom fixtures, throughout the facility. A map of the facility that indicated where patients routinely worked within the plant was also provided. DHEC staff and CDC subject matter experts conducted a site visit to collect more information about the workplace, including an overview of the cleaning and industrial processes that create aerosolized water, the usual work locations of persons who became ill, and potential areas of stagnation in the facility plumbing system.

Demographic Characteristics

Figure 1

Figure 1. Classification of cases associated with a cluster of legionellosis in a manufacturing facility in South Carolina, USA, 2022. LTFU was defined as failure to reach a patient after 3 attempts...

A total of 77 workers and other staff at the facility were investigated (Figure 1). Of those persons, 9 were lost to follow-up (defined as failure to reach a patient after 3 attempts within 1 week), 34 were excluded because they either did not meet the case definition or had documentation of an alternative etiology in their medical records, and 34 met the case definition for legionellosis. The 34 patients who met the case definition were classified further; 10 had confirmed Legionnaires’ disease, 20 had probable Legionnaires’ disease, and 4 had probable Pontiac fever (Table 1). Most employees at the facility worked first shift (n = 817 [58.1%]), followed by second shift (n = 460 [32.7%]) and third shift (n = 130 [9.2%]); employees from different shifts had the same work responsibilities. The overall attack rate among employees was 2.4%. The attack rate was 2.1% during the first shift, 1% during the second shift, and 3.8% during the third shift.

Figure 2

Figure 2. Epidemic curve of reported cases of legionellosis associated with a manufacturing facility and timeline of corrective actions for potential exposure sources, South Carolina, USA, 2022. Of 34 total cases, 10...

Figure 3

Figure 3. Usual work location of employees with confirmed and probable legionellosis according to shift and proximity to water jet cutters at a manufacturing facility in South Carolina, USA, 2022. Stars without...

More patients with legionellosis were male (n = 23 [67.6%]) than female (n = 11 [32.4%], and the median age was 40 years (Table 1). Fifteen patients were hospitalized because of Legionnaires’ disease. The highest proportion of hospitalizations were reported among persons who were 18–49 years of age (n = 11 [73.3%]), male (n = 10 [66.7%]), and worked during the first shift at the facility (n = 7 [46.7%]) (Table 2). Most (n = 10 [66.7%]) hospitalized patients reported illness onset began during September 2022 (Figure 2). The retrospective search for legionellosis cases in the South Carolina surveillance system identified 1 patient who tested positive for Legionella and worked at the facility, reported in May 2022. Two fatalities were reported in this cluster. No clustering of cases according to work locations within the facility was identified (Figure 3). The facility did not keep routine records of employee demographic information; therefore, no comparisons with the general population at the facility could be made.

Clinical Sampling Results

Twelve urine specimens from workers at the facility who had symptoms consistent with legionellosis were collected by their healthcare providers and were tested by using an L. pneumophila serogroup 1 (Lp1) urinary antigen test either at commercial laboratories or by the South Carolina public health laboratory. Urinary antigen tests for 10 of 12 urine specimens were L. pneumophila–positive, indicating infection was most likely from Lp1. For hospitalized patients, we coordinated with infection preventionists to collect lower respiratory specimens if the patient had received antimicrobial drugs for <7 days. We shipped 1 sputum sample to CDC for further testing and characterization. No isolate was recovered from that specimen; therefore, nested sequence-based typing (SBT) results were generated by using DNA extracted directly from the specimen (14,15). The culture-negative respiratory specimen tested at CDC was identified as Lp1 ST36.

Environmental Sampling Results

The Legionella consultant collected 316 samples from different potable and nonpotable water sources during September 2022–February 2023. Of those samples, 82 were tested in September 2022 by using qualitative PCR specific for Legionella bacteria. Legionella spp. and L. pneumophila were detected in 37 samples. In addition, 234 samples were tested by using a culture method to isolate L. pneumophila and non–L. pneumophila Legionella spp. All L. pneumophila isolates were characterized further to determine if they were serogroup 1. Lp1 was isolated from 8 different samples collected from water jet cutters 1 and 2 (Figure 3) and a floor scrubber in September and October 2022. No Legionella spp. were isolated from samples collected from other sources. L. pneumophila serogroups 2–15 were isolated from 1 sample collected from a water jet cutter in November 2022. All subsequent samples were negative for Legionella bacteria.

Nine Legionella isolates recovered from environmental samples collected at the facility in September 2022 were submitted to CDC for further characterization. CDC performed Legionella multiplex real-time PCR on the presumptive Legionella isolates and detected Lp1. CDC generated a complete SBT profile for the isolates and identified the environmental isolates as ST36, the same ST as the clinical respiratory specimen.

Environmental Assessment

The facility provided the following list of records that they maintained: cooling system maintenance records, facility and water inventory maps, Legionella Environmental Assessment Form, preventive and maintenance work instructions, safety data sheets, water management plan, and water system inventory. Two water jet cutters were present in the facility and were used on all shifts. The machinery works by combining garnet and water from the premise plumbing system under high pressure to cut parts from sheet metal. The garnet/water mixture is pumped through a circulation loop where the garnet is separated and water is returned to a catch basin. The plant operators had previously determined the basin temperature to be 35°C–40°C during use. The cutting piece and water catch basin were open to the environment, permitting aerosols and water spillage onto the surrounding area.

Floor scrubbers that capture water, sediment, and other particulates throughout the facility were used during all shifts. The manually operated machines sprayed water and detergent on the floor, where the mixture was then spread by large circular brushes and vacuumed into a collection tank. Spray from the machines and the scrubbing motion of the brushes are capable of producing aerosols that could spread Legionella bacteria. Although the facility has 5 floor scrubbers, only 1 tested positive for Legionella bacteria during this investigation. The area around the water jet cutters was frequently cleaned by the floor scrubbers to remove standing water on the floor resulting from overspray and overflow from the machinery.

Environmental Control Measures

Company management shut down both water jet cutters and discontinued use of all floor scrubbers after receiving the initial Legionella sampling results. The water jet cutters and floor scrubbers were turned off on September 18, 2022. The water jet cutters were returned to service on November 16, 2022. Although we provided the facility with recommendations on how to safely return the floor scrubbers to service on October 20, 2022, the facility management decided against putting them back in service and used backup scrubbers instead. In response to the legionellosis cluster, the water jet cutter control plan consisted of mechanical preventive measures, such as inspection, cleaning, maintenance, and filter change. The company developed chemical prevention measures, including biocide feed, water quality tests, pump inspections, and the use of slow dissolving tablets of the wide-spectrum biocide, 2,2-dibromo-3-nitrilopropionamide (92%–98%), which can achieve a 4-log reduction in Legionella bacteria concentrations when used in appropriate concentrations and causes less corrosion than chlorine (16).

Floor scrubber remediation measures consisted of regular mechanical preventive maintenance and disinfection, which included adding chlorine bleach to the recovery tank and filling the tank with clean water. Postremediation samples collected from both the water jet cutters and the floor scrubber were negative for Legionella spp.