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Legionellosis -- Staffordshire, England, and Wayne County, Michigan

The largest reported outbreak of legionellosis outside the United States occurred during April and early May 1985 in Staffordshire, England. During this period, 158 persons were hospitalized with acute respiratory infections; 36 (23%) of these cases have been fatal. To date, 60 patients have laboratory evidence of legionellosis, including 11 of the fatal cases. Patients are predominantly elderly, and most reside within an 8-10 mile area. The only common exposure noted among the 50 confirmed cases was a visit to the Outpatient Department (OPD) at the Stafford District General Hospital. A case-control study to confirm this association and to define specific exposures within the OPD is under way. Most visits to the OPD occurred in the week following Easter vacation. The OPD was not open during the vacation period, and the water supply was not circulating at that time. Samples from the potable water system have been negative for Legionella to date. There is also a cooling tower from the air conditioning system in the vicinity of the OPD, and L. pneumophila serogroup 1 has been isolated from water samples. The cooling tower and the potable water system have been chlorinated, and the potable hot water system temperature has also been increased. No further cases have occurred.

An outbreak of legionellosis also occurred in Michigan during early May. Fourteen cases of pneumonia with high fever have been identified in the approximately 380 persons who attended a church banquet at a hotel on April 27; three (21%) of these cases have been fatal. To date, seven cases have laboratory evidence of legionellosis, including all the fatal cases. No common exposures other than attending the banquet have been identified. Samples of the hotel's potable water, a nearby swimming pool and whirlpool, and the 12 functioning heat and ventilation air conditioning units have been obtained. Washings obtained from the external surface of the cooling coils of both air conditioning units supplying the banquet hall have grown L. pneumophila serogroup 1. Passive surveillance of the over 800 persons attending 12 other banquets held at the hotel between April 25 and May 10 has identified only one suspected case with pneumonia. No recent cases have been identified. Reported by The Communicable Disease Surveillance Center, London, England; KA Tait, MPH, DW Lawrenchuk, MD, V Vangieson, DVM, Wayne County Health Dept, Michigan, WN Hall, MD, KR Wilcox, Jr, MD, Michigan Department of Public Health; Respiratory and Special Pathogens Epidemiology Br, Div of Bacterial Diseases, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: Legionnaires' disease occurs in epidemic and sporadic forms. Sporadic cases outnumber the epidemic cases; an estimated 25,000-50,000 cases of sporadic legionellosis occur in the United States each year (1). Despite this, the occurrence of large outbreaks, such as that in Staffordshire, underlines the continuing public health hazard of epidemic legionellosis. During outbreaks, attack rates tend to be highest in specific high-risk groups, including the elderly, smokers, and immunocompromised persons.

Epidemic legionellosis usually results from exposure of susceptible individuals to an aerosol generated by an environmental source of water contaminated with Legionella. In previous outbreaks, disease has been associated with exposure to evaporative condensers, cooling towers, showers, whirlpools, and respiratory therapy equipment (2-6). A specific source has not yet been epidemiologically implicated in either of these recent outbreaks. Recovery of Legionella from an environmental site does not by itself constitute proof of the source of the outbreak because Legionella is frequently isolated from water sources unrelated to outbreaks of human disease. Additional efforts must be made to find an association between exposure to a given potential source of the organism and occurrence of the disease, including appropriate epidemiologic studies, specific sub-typing of Legionella isolates, and identification of a mechanism of aerosol generation that could allow transmission to occur (7). Further epidemiologic and laboratory investigation of potential environmental sources is currently under way in both outbreaks.

Routine testing of potable water systems or cooling towers for L. pneumophila is of questionable value and, therefore, has not been recommended, since the organism is ubiquitous, and the significance of a positive culture in the absence of associated illness cannot be defined. In addition, routine decontamination of potable water systems or cooling towers specifically directed at Legionella is not without hazard. Routine treatment with biocides active against Legionella does not necessarily eradicate the organism (8). Studies are under way to determine the settings in which Legionella causes human disease and to evaluate effective control measures.


  1. Foy HM, Broome CV, Hayes PS, Allan I, Cooney MK, Tobe R. Legionnaires' disease in a prepaid medical-care group in Seattle 1963-75. Lancet 1979;I:767-70.

  2. Dondero TJ, Rendtorff RC, Mallison GF, et al. An outbreak of Legionnaires' disease associated with a contaminated air-conditioning cooling tower. N Engl J Med 1980;302:365-70.

  3. Spitalny KC, Vogt R, Witherell L, et al. Legionnaires' disease and Pontiac fever associated with a whirlpool. Miami Beach, Florida: 22nd Interscience Conference on Antimicrobial Agents and Chemotherapy, 1982 (abstract #87).

  4. Shands KN, Ho JL, Gorman GW, et al. Potable water as a source of Legionnaires' disease. Clin Res 1981;29 (abstract #260A).

  5. Jones E, Checko P, Dalton A, et al. Nosocomial Legionnaires disease associated with exposure to respiratory therapy equipment, Connecticut. In: Legionella. Thornsberry C, Balows A, Feeley JC, Jakubowski W, eds. Washington D.C.: ASM, 1984:225-7.

  6. Cordes LG, Wiesenthal AM, Gorman GW, et al. Isolation of Legionella pneumophila from hospital shower heads. Ann Intern Med 1981;94:195-7.

  7. Broome CV. Epidemiologic assessment of methods of transmission of legionellosis. Zbl Bakt Hyg, I. Abt. Orig. A 1983;255:52-7.

  8. Fliermans CB, Harvey RS. Effectiveness of 1-Bromo-3-Chloro-5, 5-Dimethylhydantoin against Legionella pneumophila in a cooling tower. Applied Environ Microbiology. 1984;47:1307-10.

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