Legionellosis is caused by Legionella bacteria and can present as Legionnaires’ disease or Pontiac fever. Legionnaires’ disease typically presents as pneumonia and frequently requires hospitalization. Pontiac fever is a milder illness characterized by symptoms of fever and muscle aches. Most Legionella infections in humans are caused by Legionella pneumophila serogroup 1 (Lp1). Transmission of Legionella occurs through inhaling aerosolized water droplets or aspirating water that contains the bacteria. In water systems, stagnation, warm temperatures, and sediment can facilitate Legionella growth and subsequent risk for legionellosis (Sciuto et al., 2021). Legionellosis outbreaks have been commonly associated with aerosolizing water sources such as showers, hot tubs, decorative fountains, and cooling towers (Centers for Disease Control and Prevention [CDC], n.d.).

Nationally and in Tennessee, legionellosis cases have increased during the past 2 decades to 3 cases per 100,000 population (Barskey et al., 2022; Tennessee Department of Health [TDH], n.d.). Shelby County includes Memphis and has a population estimated at 1 million individuals. In Shelby County, an average of 3 legionellosis cases a month have been identified during the past 10 years. In Tennessee, all positive test results for Legionella are reported to public health departments. After notification of a patient with positive test results for Legionella, health departments routinely collect information that includes chest radiograph results from medical records and interviews patients about symptoms, date of illness onset, and potential exposures (e.g., healthcare facilities, hotels, whirlpool spa).

In May 2023, the Shelby County Health Department (SCHD) initiated an outbreak investigation after identifying 3 people with Legionnaires’ disease whose only common reported exposure was attending the same church during the 14 days before illness onset. To identify the Legionella source and prevent additional illnesses, SCHD and the Tennessee Department of Health (TDH) initiated epidemiologic, environmental, and laboratory investigations.

Initial case ascertainment occurred through routine public health surveillance. After initiating the outbreak investigation, SCHD implemented an enhanced legionellosis survey questionnaire, which also included questions about attendance at places of worship, community events, retail shops, and grocery stores in subsequent interviews. SCHD officials also asked the Mississippi Department of Health for information about recent legionellosis illnesses among Mississippi residents because of that state border’s proximity to the church and concurrent admission of Mississippi residents for legionellosis at the same hospital as the initial Tennessee cases.

An outbreak-specific survey was developed and administered among church attendees to facilitate finding cases and assessing exposure (Supplemental Survey, www.neha.org/jeh-supplementals). The survey included questions about demographic information and if the church participants had experienced symptoms (e.g., fever, muscle aches, cough, difficulty breathing) ≤14 days after having attended an event at the church.

If a participant reported symptoms, they were asked about healthcare facility visits and if they had either a chest radiograph or a test for legionellosis. Survey questions about church attendance included what day of the week they had attended a service, which events they attended, where they sat, and if they had used a bathroom. Additionally, church leadership invited their congregation to complete the online survey by email. The survey link was also posted on the church website and a telephone number for SCHD was provided for anyone who wanted to complete the survey by telephone. Survey data were collected and managed using REDCap (Research Electronic Data Capture) tools hosted at TDH (Harris et al., 2009, 2019).

The outbreak case definition was self-reported fever, muscle aches, or cough ≤14 days of attending the church in person between April 1 and April 30, 2023, which was before initial remediation measures. If laboratory confirmation of legionellosis was established (e.g., Lp1 was detected by urinary antigen testing), cases were classified as confirmed Legionnaires’ disease; otherwise, they were classified as probable legionellosis. Individuals responding to the survey who did not have symptoms of legionellosis and who had attended the church after April 1 composed the control group. We used SAS version 9.4 to conduct chi-square (or Fisher’s exact tests for cells with <5 observations) to compare frequency of exposures among cases and the control group.

SCHD and TDH officials conducted an on-site environmental assessment, where they asked staff about the source and management of water as well as the use, maintenance, and layout of the building. Next, 1 L of water was collected from locations identified as plausible sources of Legionella (e.g., kitchen, bathrooms, baptismal font) using l-L bottles that contained sodium thiosulfate. Surfaces in contact with water were sampled using environmental sponge-stick swabs with a neutralizing buffer (3M). Water samples and swabs were stored and transported under refrigerated conditions (2–8 °C). An ExTab reagent was dissolved in an additional 20 ml of water from each source and total chlorine levels and water temperature were measured using a handheld meter (EXTECH EX900, Grainger Industrial Supply) with a minimum detection limit of 0.01 ppm . SCHD asked local health systems that were treating people with Legionnaires’ disease to send clinical respiratory specimens to the TDH Division of Laboratory Services (TDH-DLS) for Legionella testing.

TDH-DLS tested for Legionella in all environmental samples via culture and tested water samples via real-time polymerase chain reaction (PCR) testing. Water samples were vacuum filter-concentrated through a 0.2-μm polycarbonate filter. The filter was then placed in 5 ml of sterile water and vortexed to free the bacteria and organic material. Next, 1 ml of the filtered sample was added to a sterile cryotube for Legionella PCR extraction, and 0.1 ml of the mixture was spread on buffered charcoal yeast extract and glycine-vancomy-cin-polymyxin-cycloheximide (BYCE-GVPC) agar plates (Remel, Thermo Fisher Scientific) for culture. For PCR testing, iQ-Check Legionella Real-Time PCR kits were used with the CFX96 Touch Real-Time PCR Detection System (Bio-Rad).

Suspect isolates of Legionella grown in culture were identified by matrix-assisted laser desorption/ionization (MALDI)–time of flight mass spectrometry (Bruker micro-flex used with RUO database version 4.3.18, Bruker Daltonics). Legionella serogroup was determined by latex agglutination. Isolates of L. pneumophila were sent to the Centers for Disease Control and Prevention (CDC) for further characterization. Isolates were first screened for genetic diversity by sequencing their mompS locus and determining the mompS allele numbers based on the European Society of Clinical Microbiology and Infectious Diseases Study Group for Legionella Infections (ESGLI) allele database. Although the database has not been publicly accessible since 2020, it is curated by UK Health Security Agency staff, and inquiries can be sent to legionella-sbt@ukhsa.gov.uk. A full (SBT)-based typing profile of seven L. pneumophila loci was generated for a subset of isolates (Lück et al., 2013).

This activity was reviewed and deemed not research by CDC and was conducted consistent with applicable federal law and CDC policy (45 C.F.R. § 46.102[1][2]; 21 C.F.R. § 56; 42 U.S. Code 241 [d]; 5 U.S. Code § 552a; 44 U.S. Code § 3501 et seq.).

We identified a legionellosis outbreak with 16 cases associated with a local church. Growth of Lp1 (the serogroup detected by urinary antigen testing) from the baptismal font, coupled with the temporality of congregational exposure after filling and operation of the font, support the baptismal font as the primary source of exposure. Although Lp1 was isolated also from the women’s restroom behind the auditorium, we did not attribute illnesses to this location because the restroom was minimally used. Established partnerships among TDH, SCHD, TDH-DLS, and CDC facilitated the appropriate environmental testing and subsequent identification of a novel L. pneumophila sequence type.

Temporary building closures that were implemented during the COVID-19 pandemic might have created conditions that promoted the growth and proliferation of Legionella in stagnant water systems, although the association of building closures and Legionella growth remains unclear in the literature (Dowdell et al., 2023; Liang et al., 2021). The jetted baptismal font was filled for the first time in February 2023 since the beginning of the pandemic in 2020. Water in the church water system that supplied the baptismal font was probably colonized, with further bacterial replication possibly occurring during water stagnation (i.e., while the font was unused for at least 2 years). Because building reopenings might present opportunities for increased spread of Legionella, assessment of trends and changes in facility water use is essential during investigations of community legionellosis clusters.

Churches and other faith-based buildings are uncommon sources of legionellosis outbreaks. Church staff were unaware that water in the building could harbor pathogens such as Legionella, and the church did not have a water management program, which is similar to many other facilities that have been implicated in Legionnaires’ disease outbreaks (Clopper et al., 2021).

We discerned a need to increase our trustworthiness with church leaders, who shared concerns about detrimental consequences to church attendance from public health responses. They feared that this outbreak, occurring shortly after stay-at-home orders related to the COVID-19 pandemic, might result in the church closing. Public health personnel strove to build trust through frequent and transparent communication, which included sharing tailored educational resources (CDC, 2016, 2024a; TDH, 2019), laboratory test results, and next steps as information became available. We also strove to honor the church’s priorities during the response (e.g., allowing services to continue in a different location, identifying firms that could quickly complete remediation).

During this investigation, we also identified that facilities such as churches with limited resources might experience financial and logistical barriers to implementing water management programs compared with well-resourced facilities. For example, churches do not have the professional guidance that healthcare facilities do, which have guidelines from professional societies such as ASHRAE (n.d.).

Moreover, professional guidelines specifically adapted for water management in community settings with limited resources might have benefited this outbreak response by providing recommendations that were more suited to church facilities, including the jetted baptismal font. We initially developed specific flushing guidance and a water management program for the church with the assistance of the local utility provider.

Although the church implemented this guidance, repeated environmental testing identified Lp1 bacteria 2 months after initial testing, which required the church to hire a remediation firm. Thus, public health partnerships with engineering and plumbing specialists to adapt water system maintenance guidance for buildings operated by resource-limited organizations could help prevent Legionella outbreaks in community settings and avoid costly remediation efforts.

In this legionellosis outbreak, environmental sampling in a church identified the likely L. pneumophila source as the immersive jetted baptismal font. Water stagnation in church plumbing during closures related to the COVID-19 pandemic might have increased Legionella risk when the baptismal font was refilled. Increased awareness of legionellosis risks and the importance of water management—including when reopening buildings (CDC, 2024b)—is needed among faith-based organizations. Collaboration with engineering and plumbing specialists is needed because public health agencies can be limited in providing expertise and resources for mitigating legionellosis risk in facility water systems in uncommon outbreak settings.