Legionnaires Disease Associated with a Private-Use Hot Tub in a Vacation Rental Property — New York, October 2024–April 2025

Abstract

In mid-October 2024, the New York State Department of Health (NYSDOH) was notified of two cases of Legionnaires disease in persons who stayed at the same short-term vacation rental property and had both used the rental property’s hot tub. The diagnoses were confirmed by urine antigen tests, and NYSDOH successfully isolated Legionella pneumophila serogroup 1 from the sputum of one patient. Local health department staff members collected three samples from three sinks and two samples from two showers to assess the rental property’s potable water system, which was supplied by a private well. Three samples were also collected from the rental property’s hot tub. Whole genome sequencing of isolates from the hot tub samples and the sputum specimen were closely related, suggesting that the hot tub was the likely source of exposure. Hot tubs create aerosols and typically maintain water temperatures of approximately 100°F–104°F (38°C–40°C). This temperature is within the most favorable range for Legionella growth and also accelerates the decay of disinfectants. Guidance from NYSDOH and CDC regarding proper operation, disinfection, and remediation of hot tubs was provided to the rental property owner. NYSDOH recommended that the owner close the hot tub until proper remediation was performed and postremediation samples without detection of any Legionella bacteria were collected by NYSDOH staff members. The rental property owner did not initially comply with NYSDOH recommendations, and a public nuisance law was used to ensure that proper measures were taken to disinfect the hot tub before use by future guests. Activities to raise awareness among short-term rental and vacation rental property owners regarding the risks associated with an improperly managed hot tub are needed to decrease the likelihood that rental property hot tubs are in a condition that is conducive to Legionella growth and reduce the risk for Legionnaires disease associated with vacation rental stays. Travelers staying in vacation rental properties should be aware that use of hot tubs might pose a risk for Legionnaires disease and exercise caution when using hot tubs, particularly those travelers with underlying medical conditions.

Introduction

In mid-October 2024, the New York State Department of Health (NYSDOH) was notified of an increase in in the number of reported cases incidence of Legionnaires disease in a western New York county (county A). Five patients in the same city (city A) had received positive urine antigen test (UAT) results, indicating recent exposure to Legionella pneumophila serogroup 1 (during 2022–2024, county A averaged 22 cases per year. Two of these patients were family members who had spent several nights together at a short-term vacation rental property in city B, 40 miles south of city A. NYSDOH began an investigation of the rental property in an effort to ascertain the extent of this outbreak, identify any additional cases, and investigate any potential sources of exposures so that proper remedial and preventive action could be taken.

Investigations and Results

Epidemiologic Investigation

Initial investigation. Epidemiology staff members from the local health department interviewed five persons (patients A, B, C, D, and E) who received positive UAT results using the NYSDOH Legionnaires Disease Questionnaire (part of the standard case report form developed based on CDC’s Legionella case report form) (Table 1). Two family members (patients A and B) who had stayed together at the rental property and had both used the hot tub, sauna, and shower reported similar symptom onset dates during the first week of October 2024. This outbreak investigation work represents standard public health practice by NYSDOH, and institutional review board review was not required.

Investigation of the rental property (patients A and B). After identification of the common exposures of patients A and B, and because Legionnaires disease has been associated with hot tub use (1,2), an investigation of the rental property was conducted. A confirmed case of Legionnaires disease associated with the rental property was defined as receipt of a positive UAT or Legionella species culture result in a person with a clinically compatible illness who reported a stay at the rental property in October 2024. Patient A and patient B experienced cough, fever, and chills. Patient A, who had comorbid conditions, was hospitalized and received antibiotics and invasive mechanical ventilation (Clinical Guidance for Legionella Infections | CDC) (Table 1). Patient A survived but the hospital discharge date is not known. Patient B visited an emergency department and was prescribed antibiotics but was not admitted. The results from a sputum sample collected from patient A were initially negative at a commercial laboratory. NYSDOH requested that the specimen be forwarded to the Wadsworth Center David Axelrod Institute (WC-DAI), a public health laboratory operated by NYSDOH, for further testing. No clinical specimen was collected from patient B. A line list of patients with Legionnaires disease associated with the rental property was developed by NYSDOH, which included demographic characteristics, signs and symptoms, underlying medical conditions, symptom onset date, travel and exposure history, and diagnostic testing results. Retrospective and prospective reviews of case exposure histories did not identify any additional cases associated with the rental property.*

Investigation of patients C, D, and E. A separate cluster investigation was conducted for patients C, D, and E; no common exposures were identified among these patients (Table 1). A potential occupational exposure was investigated for patient C, but no source was identified.

Rental Property Environmental Health and Laboratory Investigation

Collection of samples. Eight samples were collected from the rental property (Table 2): five potable water samples from the sinks and showers, two swabs of hot tub surfaces, and one nonpotable water sample collected directly from the hot tub basin. Each water sample was initially collected into a sterile 34-oz (1-L) bottle and subsequently divided into 4-oz (120-mL) and 10-oz (290-mL) sterile plastic bottles containing sodium thiosulfate, which was used to neutralize chlorine in the sample and prevent further disinfection during transport to the laboratory and to ensure preservation of any viable Legionella species present in the sample.^†

Analysis of water samples. All eight collected water samples were submitted to the Wadsworth Center Environmental Biggs Laboratory for analysis both by IDEXX’s Legiolert and by standard culture (International Organization for Standardization [ISO] 11731:2017) (3). Legiolert is a culture-based method that can be conducted more quickly (7 days) than standard culture (10–14 days).^§ Use of both methods increases the chances of recovering an organism and increases the likelihood of detecting any Legionella species in the sample.

Analysis of swab samples. Because the Legiolert test is only intended for use with water samples, the laboratory created a modified protocol for use with swabs. Swabs were prepared according to ISO 11731:2017 (3), generating 1:10 and 1:100 serial dilutions in phosphate-buffered saline. A 0.03-oz (1-mL) aliquot of each dilution was added to 3 oz (99 mL) of reagent water (highly purified water with no detectable concentration of the compound or element to be analyzed) and processed according to the manufacturer’s instructions for potable water.

Identification of L. pneumophila from hot tub samples. Legiolert detected L. pneumophila in all three hot tub samples, ranging from 134 to 13,677 most probable number (MPN) of colonies per milliliter^¶ (Table 2). Legiolert did not detect L. pneumophila in the potable water system samples. Standard culture (ISO 11731:2017) confirmed the presence of Legionella species in one sample, the swab from the air-water interface of the hot tub (3,700 colony-forming units per milliliter). The potable water samples were found to contain a total and free chlorine residual >10 mg/L, and the sodium thiosulfate contained in the sterile plastic bottles used for sample collection can neutralize up to 15 mg/L of chlorine, suggesting the presence of >25 mg/L. The high residual chlorine level would normally result in rejection of a sample, but the laboratory agreed to analyze these samples at the request of NYSDOH even though isolation of viable Legionella organisms from the potable water samples was deemed highly unlikely.

Whole genome sequencing (WGS) of isolates. WC-DAI performed the analysis and WGS of clinical specimens and environmental samples. A sputum sample from patient A that initially tested negative by culture at a commercial laboratory was forwarded to WC-DAI, which isolated L. pneumophila serogroup 1 via culture. The isolates from the hot tub differed by two to three single nucleotide polymorphisms from patient A’s clinical isolate, indicating that they were closely related.

Public Health Response

Recommendations to the Rental Property Owner

Discussion between NYSDOH and the property manager revealed that the owner had disinfected the private well with a large amount of liquid chlorine bleach the night before health department officials were scheduled to visit the site. NYSDOH staff members learned that the hot tub was not regularly disinfected and recommended the hot tub immediately be closed to guests until it was cleaned professionally, and a chemical treatment program was implemented. CDC guidance was provided to the property owner (4), who was instructed to notify NYSDOH when proper remediation of the hot tub was completed.

Follow-Up After Remediation Recommendations

Approximately 4 weeks after sample collection and recommendations were provided to the rental property owner, local health department officials informed NYSDOH that the hot tub was back in use; NYSDOH had not been notified by the property owner. The rental property owner had personally cleaned the hot tub (i.e., did not hire professionals), tested a sample using an unapproved method, and reopened the hot tub for guest use without consulting NYSDOH. NYSDOH staff members reiterated the importance of having the equipment cleaned professionally and allowing NYSDOH staff members to collect the samples for analysis by a laboratory certified by the New York Environmental Laboratory Approval Program (5). After an additional 4 weeks, NYSDOH staff members were notified that the rental listing still advertised the hot tub, and guests were leaving new reviews that mentioned hot tub use.

Use of the New York Public Nuisance Law

Because the hot tub had not been satisfactorily disinfected, and the rental property owner continued to allow its use by guests, local health department officials charged the owner with violation of the Erie County Sanitary Code, and the hot tub was deemed a public nuisance. The health department also issued a commissioner’s order to close the hot tub until it was deemed safe to use.

Subsequent Remediation and Testing Results

After the hot tub was cleaned and disinfected by a professional, two rounds of follow-up sampling were conducted by the local health department staff members. The commissioner’s order was lifted on March 31, 2025, after two successive rounds of sampling from the hot tub did not identify any viable Legionella organisms. The professional hired by the rental property to clean the hot tub was subsequently hired to service it weekly.

Discussion

By positively matching an environmental source of L. pneumophila with Legionnaires disease cases (6), WGS determined that the clinical specimen collected from patient A was closely related to the environmental samples collected from the hot tub, thereby establishing it as likely source of infection. Rental property hot tub use is frequently associated with reports of Legionnaires disease, and NYSDOH has successfully matched clinical samples from persons with Legionnaires disease to environmental samples from hot tubs in recent years (1,6).

According to CDC’s Supplementary Legionnaires Disease Surveillance System, during 2014–2021, one in seven patients with Legionnaires disease report having stayed overnight in a hotel or vacation rental property; among those, approximately one half report having used a hot tub (1). A 2021 NYSDOH investigation concluded that at least one case of Legionnaires disease was associated with shared use of a private property hot tub (6), and CDC recently reported that two Legionnaires disease outbreaks were associated with outdoor hot tubs intended for private use on cruise ships (2). NYSDOH staff members added guidance to the program website designed to raise awareness about the risks involved with the use of an improperly managed hot tub and included guidance for proper routine water treatment practices.** New York has regulations designed to prevent Legionella contamination in cooling towers and in certain health care facilities^†† (7) and to ensure that proper sanitary practices are followed in public pools (8); however, residential spa pools, including those at homes rented for overnight occupancy, are exempt from both regulations.

Implications for Public Health Practice

Health department officials who perform waterborne disease investigations should prioritize testing any identified hot tub as a potential source of exposure when Legionnaires disease cases meet CDC’s outbreak definition (9). Public health officials should conduct on-site field visits, collect and test samples, and use all available tools, including public nuisance laws if needed, to protect public health. Regular postremediation follow-up samples should be collected to ensure long-term control. Vacation and other short-term rental property owners should be informed of the risks associated with improperly managed hot tubs, particularly for persons at increased risk for severe illness, including those with underlying medical conditions.