Environmental cultures.

Q Should a clinical microbiology lab in a community hospital be doing environmental cultures on specimens collected in the hospital? I am referring specifically to culturing of deionized water, swabs of cleaned whirlpools in physical therapy, water samples from cleaned endoscopes, water from dialysis tubing, and sterilized spore strips from the operating room and central processing. If it is appropriate, are there any references to use as guidelines for procedures and interpretation of results?

A The routine microbiologic sampling of the hospital environment is not useful or cost effective unless it is performed for a specific epidemiologic purpose (e.g., investigate a cluster of nosocomial respiratory infections), to monitor sterilization processes, or to detect contamination of water used in the dialysis unit and the laboratory. Therefore, the need to perform environmental cultures should be determined by the members of the infection-control committee and to include, as a minimum, a representative from the microbiology laboratory, the hospital epidemiologist, and the infection control practitioner. The specimens should be sent to an appropriate reference laboratory in the event that the hospital laboratory cannot perform the cultures.

After approval by the infection control committee, the microbiology laboratory must apply the appropriate procedure and interpretive guideline for the myriad of potential specimens that may be submitted for culture. The problem confronting the microbiology laboratory is that the procedures for culturing potential environmental specimens are scattered among numerous publications, associations, societies, governmental agencies, and organizations. For example, NCCLS (www.nccls.org) publishes a procedure for the evaluation of laboratory water. (1) The Association for the Advancement of Medical Instrumentation (www.aami.org) publishes standards for the water used to prepare dialysate used in dialysis units. These standards include the procedures and interpretive guidelines for endotoxin contamination and total viable microbial counts in the water. Often, the dialysis unit has a copy of these standards. The American Society for Microbiology (www.asmusa.org) publishes a handbook containing procedures for evaluating sterilization processes and culture of water and other environmental specimens. (2) Additional information can be obtained from the Centers for Disease Control and Prevention (www.cdc.gov/ncidod/hip) on healthcare guidelines; the American Public Health Association (www.apha.org) on standards for the examination of water and wastewater; and other selected publications. (3,4) Also, the members of the infection control committee are a valuable resource for identifying a source for a specific procedure.

References

1. NCCLS. Preparation and testing of reagent water in the clinical laboratory. 1997.

2. Gilchrist MRJ, ed. Epidemiologic and infection control microbiology. In: Clinical Microbiology Procedures Handbook, Isenberg HD, ed. American Society for Microbiology. 1992;pp:11.0.1-11.17.4.

3. Mietzner SM, Stout JE. Laboratory Detection of Legionella in Environmental Samples. Clin Microbiol Newsl. 2002;24:81-85.

4. Wenzel R. Prevention and Control of Nosocomial Infections. Lippincott, Williams and Wilkens. 1993. New edition 2003.

--David Sewell, PhD, ABMM 

Director of Microbiology Veterans Affairs Medical Center

Portland, OR