The use of molecular techniques in the epidemiology and control of infectious diseases

The ability to identify specific strains within a given species of pathogen is an important aid in the rational development of effective measures to prevent and control nosocomial infections. The efforts of both microbiologist and hospital epidemiologic are facilitated greatly by the availability of the newer molecular epidemiologic typing techniques. Although these methods clearly have limitations, they generally are a significant improvement over the more conventional typing methods, many of which are too cumbersome, insensitive, and time-consuming to be of practical value for epidemiologic evaluations. Based on current experience, the molecular typing methods that appear to be the most practical and useful for both large and small scale epidemiologic studies are the DNA-based methods of REAP and PFGE. Many questions remain concerning the appropriate role of molecular typing methods in the clinical microbiology laboratory. Often, molecular typing may be performed more efficiently in a reference laboratory. In contrast, selected methods such as plasmid analysis are well within the scope of clinical microbiology laboratories and may be an important adjunct to the hospital infection control effort. Given the limitations of the available methods and the complex nature of patients at risk for nosocomial infections, it is imperative that these methods be employed with clear epidemiologic objectives in mind. Typing should always include unrelated as well as epidemiologically related isolates and, whenever possible, all organisms should be typed under identical conditions, preferably within the same test run. In addition, results are most effectively used to supplement rather than to replace hypotheses and questions thoughtfully developed by the clinician or epidemiologist. Ideally, typing is performed independently by the laboratory to avoid bias, but the results are applied collaboratively to ensure that both the potential insights and the unavoidable ambiguities presented by the results are clearly appreciated. Additional studies based upon sound epidemiologic principles will help clarify the role of the various molecular typing methods as epidemiologic markers and advance our understanding of the epidemiology of nosocomial infections.