Environmental Reporter
Home > Resources > Education > Environmental Reporter > Legionnaires' Disease and Travel

Legionnaires' Disease and Travel

Travel-Related Legionnaires' Disease

By Dr. Harriet Burge, EMLab P&K Chief Aerobiologist and Director of Scientific Advisory Board

Legionnaires' disease continues to be an important cause of severe pneumonia in the United States. In fact, there has been a large increase in the incidence of legionellosis since 2003 (Neil & Berkelman 2008). Between 2003 and 2005, the incidence of legionellosis increased to 12,000 reported cases per year. Many pneumonias are not diagnosed specifically and therefore not reported, so actual incidence is probably much higher. The cost of treating patients with Legionnaires' disease far exceeds the cost of even intensive investigations, making the understanding of how and why Legionella colonizes human-associated reservoirs remain essential (Lock et al, 2008).

Although we know more about how Legionella occupies reservoirs that lead to human exposure, control of the most important reservoirs remains limited. Briefly, Legionella, particularly Legionella pneumophila, colonizes warm water biofilms. Once in the biofilm, the bacteria colonize amoebae, thus sequestering themselves from chlorine and other biocides. If the reservoir has the potential for releasing droplets into the air, human exposure is inevitable, and disease will occur if those exposed have the necessary risk factors.

Well recognized reservoirs for Legionella pneumophila that have resulted in human disease include cooling towers, potable water systems, hot tubs, showers, spas, fountains, and machining coolants. In fact, ANY situation that is continually wet and warm has good potential for bacterial colonization, and controlling exposure is probably not possible. Thus, those with specific risk factors need to avoid aerosols released from such reservoirs. Major risk factors for Legionnaires' disease are male gender, age greater than 60, smoking, alcohol abuse, diabetes, and, of course, diseased and immunocompromised individuals.

It is estimated that approximately 20% of hospitalized Legionnaires' disease cases are travel-related. The CDC reported 6 cases of cruise ship-related Legionnaires' disease in 1994, 8 cases in 2003-2004, and 2 clusters of travel-associated Legionnaires' disease cases in 2005 and 8 in 2006. Of the 10 clusters, 7 were associated with hotels and 3 with cruise ships. (CDC 1994, CDC 2005, CDC 2007). A summary of reports available in the ISB Web of Knowledge are presented below. This represents only a fraction of cases since most remain unreported or even undiagnosed.

Total Passengers Affected Passengers / Deaths Exposure Source Comments Authors of Report
215 8/1 Spa   Beyrer, 2007
696 3/0 Spa Same ship, 2 cruises Kura, et al., 2006
900 3/1 Water system Same ship, 3 cruises Pastoris, et al., 1999
Unknown 16 confirmed
34 probable
Spa Same ship, 9 cruises Jernigan, et al., 1996

The two most common sources for exposure to Legionella on cruise ships appear to be whirlpool spas and potable water systems. In addition to cruise ships, Legionnaires' disease associated with whirlpool spas has been reported from residential environments, retail venues, hotels, and even a flower show (Mathys et al., 2008; Vogt et al., 1987; Thomas et al., 1993; Den Boer et al., 2002; CDC 1997). Whirlpool spas appear to be ideal incubators for heat-loving bacteria, especially when they are operated 24 hours a day (as occurs on cruise ships) and can be poorly maintained. In addition, Pontiac fever, also caused by Legionella, has been reported from exposure to whirlpool spas (Mangione et al., 1985; Spitalny et al., 1984; Fallon and Rowbotham 1990).

Potable Water Systems
Potable water systems are also important sources for Legionella exposure in a variety of environments including cruise ships (Pastoris et al., 2005). One report describes Legionnaries' disease in mechanics who were exposed to Legionella in a ship's fresh water pump (Cayla et al., 2001), which affected nearly 40% of the water distribution systems. In this same study, samples from 10 cruise ships were all negative (Goutziana et al., 2008).

Residential hot water systems are also risky. In a German study, 12% of residences that had hot water tanks were Legionella positive. The primary risk factor was water temperature (Luck et al., 2008). This data should be considered when advocating energy conservation measures. In California, the Pacific Gas and Electric Company is recommending reducing hot water temperatures below 140°F, into a range that will support the growth of Legionella pneumophila.

Control of Legionella in whirlpools, water distribution systems, and other warm water sites involves rigorous attention to chlorination or other treatment methods, and periodic removal of biofilms. The CDC has published health and safety guidelines for public spas and hot tubs (CDC 1985). An important concern is new data that indicates the development of resistance to chlorine in repeatedly treated populations of Legionella (Casini et al., 2008). Thermal disinfection is not effective unless applied repeatedly. Unfortunately, Legionella pneumophila appears to be more resistant to thermal shock than less virulent species (Mouchtouri et al., 2007). Because maintenance of Legionella-free water systems is problematic, those individuals with specific risk factors should avoid exposure to water aerosols from any warm water source.

Beyrer et al. Legionnaires' disease outbreak associated with a cruise liner, August 2003: epidemiological and microbiological findings, Epidemiol. Infect. 2007; 135, 802–810.

Casini et al. Molecular epidemiology of Legionella pneumophila serogroup 1 isolates following long-term chlorine dioxide treatment in a university hospital water system, Journal of Hospital Infection 2008; 69, 141-147.

Cayla et al. A small outbreak of Legionnaires' disease in a cargo ship under repair, Eur Respir J 2001; 17: 1322–132.

Centers for Disease Control. Suggested health and safety guidelines for public spas and hot tubs. United States Department of Health and Human Services publication, 1985; 99 960. Atlanta, CDC.

Centers for Disease Control and Prevention. 1994. Outbreak of pneumonia associated with cruise ship, MMWR 1994; 43: 521.

Centers for Disease Control and Prevention. Legionnaires' Disease Associated with a Whirlpool Spa Display - Virginia, September-October, 1996; January 31, 1997; 46(04);83-86.

Centers for Disease Control and Prevention. Cruise-Ship-Associated Legionnaires' Disease, November 2003-May 2004, November 18, 2005; 54(45);1153-1155.

Centers for Disease Control and Prevention. Surveillance for Travel-Associated Legionnaires' Disease - United States, 2005—2006 December 7, 2007; 56(48);1261-1263.

Den Boer JW, et al. A large outbreak of Legionnaires' disease at a flower show, the Netherlands, 1999. Emerging Infectious Diseases 2002; 8: 37–43.

Fallon RJ, Rowbotham TJ. Microbiological investigations into an outbreak of Pontiac fever due to Legionella micdadei associated with use of a whirlpool. Journal of Clinical Pathology, 1990; 43: 479–483.

Goutziana et al. Legionella species colonization of water distribution systems, pools and air conditioning systems in cruise ships and ferries, BMC Public Health, 2008; 8:390.

Jernigan DB, et al. Outbreak of Legionnaires' disease among cruise ship passengers exposed to a contaminated whirlpool spa. Lancet, 1996; 347: 494-99.

Kura F., et al. Outbreak of Legionnaires' disease on a cruise ship linked to spa-bath filter stones contaminated with Legionella pneumophila serogroup 5,Epidemiol. Infect., 2006; 134, 385–391.

Lock et al., 2008. Public health and economic costs of investigating a suspected outbreak of Legionnaires' disease, Epidemiol. Infect. 136, 1306–1314.

Luck et al., Community-acquired Legionnaires' disease caused by Legionella pneumophila serogroup 10 linked to the private home, Journal of Medical Microbiology, 2008; 57: 240–243 DOI 10.1099/jmm.0.47382-0.

Mangione EJ, et al. An outbreak of Pontiac fever related to whirlpool use, Michigan. JAMA, 1985; 253: 535-39.

Mathys, W. et al. Occurrence of Legionella in hot water systems of single-family residences in suburbs of two German cities with special reference to solar and district heating, Int. J. Hyg. Environ. Health 211, 2008; 179–185.

Mouchtouri, V et al. Thermal disinfection of hotels, hospitals, and athletic venues hot water distribution systems contaminated by Legionella species, Am J Infect Control, 2007; 35:623-7.

Neil K, Berkelman R. Increasing Incidence of Legionellosis in the United States, 1990 2005: Changing Epidemiologic Trends. Clinical Infectious Diseases, 2008; 47:591–9.

Pastoris, MC et al. Legionnaires' Disease on a Cruise Ship Linked to the Water Supply System: Clinical and Public Health Implications, Clinical Infectious Diseases, 1999; Vol. 28, 1:33-38.

Pastoris, MC et al. Legionnaires’ disease on a cruise ship linked to the water supply system, Clinical and Microbiology, 2005; 43: 2047–2052.

Spitalny, KC et al. Pontiac fever associated with a whirlpool spa. Am J Epidemiol, 1984; 120: 809-17.

Thomas, DL et al. Hot tub legionellosis. Arch Intern Med, 1993; 153: 2597-99.

Vogt, RL et al. Legionnaires' disease and a whirlpool spa. Ann Intern Med, 1987; 107: 596.


This article was originally published on February 2009.