Skip Navigation LinksSkip Navigation Links
Centers for Disease Control and Prevention
Safer Healthier People
Blue White
Blue White
bottom curve
CDC Home Search Health Topics A-Z spacer spacer
Blue curve MMWR spacer

Persons using assistive technology might not be able to fully access information in this file. For assistance, please send e-mail to: Type 508 Accommodation and the title of the report in the subject line of e-mail.


Water Sampling Strategies and Culture Techniques for Detecting Legionellae

Legionella spp. are ubiquitous and can be isolated from 20%--40% of freshwater environments, including man-made water systems (1,2). In health-care facilities, where legionellae in potable water rarely result in disease among nonimmunocompromised patients, courses of remedial action are unclear.

Scheduled microbiologic monitoring for legionellae remains controversial because the presence of legionellae is not necessarily evidence of a potential for causing disease (3). CDC recommends aggressive disinfection measures for cleaning and maintaining devices known to transmit legionellae, but does not recommend regularly scheduled microbiologic assays for the bacteria (4). However, scheduled monitoring of potable water within a hospital might be considered in certain settings where persons are highly susceptible to illness and mortality from Legionella infection (e.g., hematopoietic stem cell transplantation units and solid organ transplant units) (5). Also, after an outbreak of legionellosis, health officials agree monitoring is necessary to identify the source and to evaluate the efficacy of biocides or other prevention measures.

Examination of water samples is the most efficient microbiologic method for identifying sources of legionellae and is an integral part of an epidemiologic investigation into health-care--associated Legionnaires' disease. Because of the diversity of plumbing and HVAC systems in health-care facilities, the number and types of sites to be tested must be determined before collection of water samples. One environmental sampling protocol that addresses sampling site selection in hospitals might serve as a prototype for sampling in other institutions (6). Any water source that might be aerosolized should be considered a potential source for transmission of legionellae. The bacteria are rarely found in municipal water supplies and tend to colonize plumbing systems and point-of-use devices. To colonize, legionellae usually require a temperature range of 77ºF--108ºF (25ºC--42.2ºC ) (7) and are most commonly located in hot water systems. Legionellae do not survive drying. Therefore, air-conditioning equipment condensate, which frequently evaporates, is not a likely source (8).

Water samples and swabs from point-of-use devices or system surfaces should be collected when sampling for legionellae (Box 1, Box 2 in text) (9). Swabs of system surfaces allow sampling of biofilms, which frequently contain legionellae. When culturing faucet aerators and shower heads, swabs of surface areas should be collected first; water samples are collected after aerators or shower heads are removed from their pipes. Swabs can be streaked directly onto buffered charcoal yeast extract agar plates if the plates are available at the collection site. If the swabs and water samples must be transported back to a laboratory for processing, immersing individual swabs in sample water minimizes drying during transit. Place swabs and water samples in insulated coolers to protect specimens from temperature extremes.


  1. Arnow PM, Weil D, Para MF. Prevalence and significance of Legionella pneumophila contamination of residential hot- tap water systems. J Infect Dis 1985;152:145--51.
  2. Shelton BG, Morris GK, Gorman GW. Reducing risks associated with Legionella bacteria in building water systems. In: Legionella: current status and emerging perspectives. Barbaree JM, Breiman RF, Dufour AP, eds. Washington DC: American Society for Microbiology Press, 1993:279--81.
  3. Joly JR. Monitoring for the presence of Legionella: where, when, and how? In: Legionella: current status and emerging perspectives. Barbaree JM, Breiman RF, Dufour AP, eds. Washington DC: American Society for Microbiology Press, 1993:211--6.
  4. Hoge CW, Breiman RF. Advances in the epidemiology and control of Legionella infections. Epidemiol Rev 1991;13:329--40.
  5. CDC. Guidelines for preventing opportunistic infections among hematopoietic stem cell transplant recipients. MMWR 2000;49(No. RR-10).
  6. Barbaree JM, Gorman GW, Martin WT, Fields BS, Morrill WE. Protocol for sampling environmental sites for Legionellae. Appl Environ Microbiol 1987;53:1454--8.
  7. Brenner DJ, Feeley JC, Weaver RE. Family VII. Legionellaceae. In: Bergey's manual of systemic bacteriology. Vol. 1. Krieg NR, Holt JG, eds. Baltimore, MD: Williams and Wilkins, 1984:279--88.
  8. Katz SM, Hammel JM. The effect of drying, heat, and pH on the survival of Legionella pneumophila. Ann Clin Lab Sci 1987;17:150--6.
  9. CDC. Procedures for the recovery of Legionella from the environment. Atlanta, GA: US Department of Health and Human Services, Public Health Service, CDC, 1992:1--13.

Healthcare Infection Control Practices Advisory Committee

Chair: Robert A. Weinstein, M.D., Cook County Hospital, Chicago, Illinois.
Co-Chair: Jane D. Siegel, M.D., University of Texas Southwestern Medical Center, Dallas, Texas.
Executive Secretary: Michele L. Pearson, M.D., CDC, Atlanta, Georgia.

Members: Raymond Y.W. Chinn, M.D., Sharp Memorial Hospital, San Diego, California; Alfred DeMaria, Jr., M.D., Massachusetts Department of Public Health, Jamaica Plain, Massachusetts; Elaine L. Larson, Ph.D., Columbia University School of Nursing, New York, New York; James T. Lee, M.D., Ph.D., University of Minnesota VA Medical Center, St. Paul, Minnesota; Ramon E. Moncada, M.D., Coronado Physician's Medical Center, Coronado, California; William A. Rutala, Ph.D., University of North Carolina School of Medicine, Chapel Hill, North Carolina; William E. Scheckler, M.D., University of Wisconsin Medical School, Madison, Wisconsin; Beth H. Stover, Kosair Children's Hospital, Louisville, Kentucky; Marjorie A. Underwood, Mt. Diablo Medical Center, Concord, California.

Liaison Members: Loretta L. Fauerbach, M.S., Association for Professionals of Infection Control and Epidemiology, Inc. (APIC), Washington, D.C.; Sandra L. Fitzler, American Health Care Association, Washington, D.C.; Dorothy M. Fogg, M.A., Association of Perioperative Registered Nurses, Denver, Colorado; Chiquita Johnson-Bond, Council of Nephrology Nurses and Technicians, Rex, Georgia; Stephen F. Jencks, M.D., Centers for Medicare and Medicaid Services, Baltimore, Maryland; Chiu S. Lin, Ph.D., Food and Drug Administration, Rockville, Maryland; Joseph G. Ouslander, M.D., Emory University, Atlanta, Georgia; James P. Steinberg, M.D., Society for Healthcare Epidemiology of America, Inc., Atlanta, Georgia; Michael L. Tapper, M.D., Advisory Committee for the Elimination of Tuberculosis, New York, New York.

CDC Consultants

Matthew Arduino, Dr.P.H.; Joe Carpenter; Rodney Donlan, Ph.D.; Lynne Sehulster, Ph.D.; Division of Healthcare Quality Promotion, National Center for Infectious Diseases (NCID); David Ashford, D.V.M., D.Sc.; Richard Besser, M.D.; Barry Fields, Ph.D.; Michael M. McNeil, M.B.B.S.; Cynthia Whitney, M.D.; Stephanie Wong, D.V.M.; Division of Bacterial and Mycotic Diseases, NCID; Dennis Juranek, D.V.M., Division of Parasitic Diseases, NCID; Jennifer Cleveland, D.D.S., Division of Oral Health, National Center for Chronic Disease Prevention and Health Promotion.

External Consultants

Trisha Barrett, M.B.A., Alta Bates Medical Center, Berkeley, California; Judene Bartley, M.S., M.P.H., Epidemiology Consulting Services, Inc., Beverly Hills, Michigan; Michael Berry, University of North Carolina, Chapel Hill, North Carolina; Nancy Bjerke, M.A., M.Ed., M.P.H., Infection Control Associates, San Antonio, Texas; Walter W. Bond, M.S., RCSA, Inc., Lawrenceville, Georgia; Cheryl Carter, University of Iowa Health Center, Iowa City, Iowa; Douglas Erickson, American Society for Healthcare Engineering (ASHE) Park Ridge, Illinois; Martin S. Favero, Ph.D., Advanced Sterilization Products, Johnson and Johnson, Irvine, California; Richard Miller, M.D., University of Louisville School of Medicine, Louisville, Kentucky; Shannon E. Mills, D.D.S., HQ USAF/Surgeon General Detail, Bolin AFB, District of Columbia; Gina Pugliese, M.S., Premier Safety Institute, Oak Brook, Illinois; Craig E. Rubens, M.D., Ph.D., Children's Hospital & Medical Center, Seattle, Washington; James D. Scott, Michigan Department of Consumer and Industry Services, Lansing, Michigan; Andrew J. Streifel, M.P.H., University of Minnesota, Minneapolis, Minnesota; Dale Woodin, ASHE, Chicago, Illinois. 

Use of trade names and commercial sources is for identification only and does not imply endorsement by the U.S. Department of Health and Human Services.

References to non-CDC sites on the Internet are provided as a service to MMWR readers and do not constitute or imply endorsement of these organizations or their programs by CDC or the U.S. Department of Health and Human Services. CDC is not responsible for the content of pages found at these sites. URL addresses listed in MMWR were current as of the date of publication.

Disclaimer   All MMWR HTML versions of articles are electronic conversions from ASCII text into HTML. This conversion may have resulted in character translation or format errors in the HTML version. Users should not rely on this HTML document, but are referred to the electronic PDF version and/or the original MMWR paper copy for the official text, figures, and tables. An original paper copy of this issue can be obtained from the Superintendent of Documents, U.S. Government Printing Office (GPO), Washington, DC 20402-9371; telephone: (202) 512-1800. Contact GPO for current prices.

**Questions or messages regarding errors in formatting should be addressed to

Page converted: 5/27/2003


Safer, Healthier People

Morbidity and Mortality Weekly Report
Centers for Disease Control and Prevention
1600 Clifton Rd, MailStop E-90, Atlanta, GA 30333, U.S.A


Department of Health
and Human Services

This page last reviewed 5/27/2003