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Legionnaires' Disease Associated With Potting Soil --- California, Oregon, and Washington, May--June 2000

Since Legionnaires' Disease (LD) was first reported in 1976, outbreaks have been associated with airborne transmission of Legionella bacteria through cooling towers, showers, and other aerosolizing devices (1). However, most LD cases are sporadic, and the source and mode of infection in many cases are unknown. Infections with one species, Legionella longbeachae, have been associated with gardening and use of potting soil in Australia and Japan (2,3). This report summarizes the findings of LD investigations in California, Oregon, and Washington, that suggest that transmission from potting soil has occurred for the first time in the United States, and that active surveillance and case finding are warranted to explore this association.

On June 13, 2000, CDC was alerted by a county health official in Washington of L. longbeachae infection in a 46-year-old woman who had been hospitalized with pneumonia. The patient reported that she had been potting plants during the 10 days before her symptoms began in May. An isolate from the patient's sputum was sent to CDC for species confirmation, and two samples of potting soil and one of compost from the original packages obtained from the patient's residence were sent for analysis. L. longbeachae was isolated from one potting soil sample. The compost contained other Legionella species but not longbeachae.

In May, two L. longbeachae isolates had been received at CDC from bronchial wash samples taken from both a 77-year-old Oregon woman and a 45-year-old California man who were both diagnosed with legionellosis. The California patient died and his house was cleaned before an investigation could be undertaken. State and local health officials determined that the Oregon patient had been potting plants using commercial potting soil mixtures and had been working in a home garden during the 10 days before her symptoms began in April. Two potting soil samples taken from her residence were tested for Legionella at CDC; one was positive for L. longbeachae. Isolates of L. longbeachae from the patients and soils will be compared using amplified fragment length polymorphism typing.

Reported by: JS Duchin, MD, J Koehler, DVM, Public Health--Seattle & King County, Seattle; JM Kobayashi, MD, State Epidemiologist, Washington State Dept of Health; RM Rakita, MD, K Olson, MD, NB Hampson, MD, Virginia Mason Medical Center, Seattle. DN Gilbert, MD, JM Jackson, Providence Portland Medical Center, Portland; KR Stefonek, MPH, MA Kohn, MD, State Epidemiologist, Oregon Dept of Human Svcs, Health Div. J Rosenberg, MD, D Vugia, MD, Acting State Epidemiologist, California Dept of Health Svcs. M Marchione-Mastroianni, CDC Foundation, Atlanta, Georgia. Respiratory Diseases Br, Div of Bacterial and Mycotic Diseases, National Center for Infectious Diseases; and EIS officers, CDC.

Editorial Note:

The findings in this report illustrate the importance of reporting cases of LD to local and state health officials and of culturing patient specimens for Legionella. Although urine antigen tests provide rapid and accurate diagnosis of Legionella pneumophila serogroup 1, these tests are not sensitive for other serogroups or species. Microbiologic and epidemiologic investigations are needed to identify less common species and may reveal risk factors and novel modes of disease transmission.

L. pneumophila serogroup 1 accounts for most legionellosis cases in the United States; L. longbeachae is reported less frequently. During 1990--1999, 37 cases of L. longbeachae were reported to CDC's Legionella reporting system. It is likely that legionellosis is underreported to CDC because of failure to obtain the appropriate diagnostic tests in cases of pneumonia of unknown etiology, difficulty of culturing Legionella from clinical specimens, and because legionellosis is not reportable in all states.

Soil surveys for Legionella have not been conducted in the United States; however, in a soil survey in Australia, 33 (73%) of 45 potting soil samples tested positive for Legionella; 26 (79%) of the 33 contained longbeachae (4). Nineteen (100%) soil samples in Europe and the United Kingdom were negative for L. longbeachae. A survey of 17 soil samples in Japan in 1998 yielded 31 different strains of Legionella; eight of the 17 samples (47%) contained L. longbeachae (3).

Health-care providers should report legionellosis cases to local or state health departments, and state health departments should report legionellosis cases, particularly L. longbeachae to CDC. Risk factors and behaviors associated with transmission of L. longbeachae are unknown; therefore, to better define the extent of disease, modes of transmission, and to develop prevention strategies, CDC urges state health departments to send Legionella cultures yielding non-pneumophila isolates to CDC's Legionella laboratory for speciation, telephone (404) 639-3563. Cases of L. longbeachae infection that have occurred during the previous 12 months should be reported to CDC's National Center for Infectious Diseases, Division of Bacterial and Mycotic Diseases, Respiratory Diseases Branch, telephone (404) 639-2215. For local and state use, a case report form may be obtained from the World-Wide Web,, and faxed to (404) 639-3970.


  1. Fiore AE, Nuorti JP, Levine OS, et al. Epidemic Legionnaires' disease two decades later: old sources, new diagnostic methods. Clin Infect Dis 1998;26:426--33.
  2. Steele TW, Lanser J, Sangster N. Isolation of Legionella longbeachae serogroup 1 from potting mixes. Appl Environ Microbiol 1990;56:49--53.
  3. Koide M, Saito A, Okazaki M, et al. Isolation of Legionella longbeachae serogroup 1 from potting soils in Japan. Clin Infect Dis 1999;29:943--4.
  4. Steele TW, Moore CV, Sangster N. Distribution of Legionella longbeachae serogroup 1 and other Legionella in potting soils in Australia. Appl Environ Microbiol 1990;56:2984--8.

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