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From The Editor
The lead article written by Ellen Jo Baron for this issue of the On-DEMAND Report, contains something of a revelation. Starting with the use of culture-based methods for proving the etiology of nosocomial diarrhea, the article chronicles the evolution of testing methods for C. difficile over the years. Culture-based methods, especially when coupled with detection of toxin-producing strains, were invaluable as aids in the epidemiologic correlation of C. difficile with nosocomial infection, but ultimately proved to be impractical for the management of patients with suspected C. difficile infection. The turnaround time for culture-based tests is several days, with results arriving long after physicians have already made up their minds as to the probability of infection.
According to several recent studies cited in this article, toxin tests vary in sensitivity levels to as low as 33%, making toxin detection a poor surrogate for detection of the infectious agent itself. From a practical standpoint, this means that many, if not most, cases of C. difficile are not currently subjected to isolation procedures that could ameliorate transmission of C. difficile in the healthcare setting. Considering the number of patients who serve as unmitigated reservoirs, perhaps it is no coincidence that C. difficile rates nationwide have risen at a pace that parallels the introduction of these tests. For laboratorians, this is an opportunity for reflection: How did we get it so wrong for so long? Over the next few years, there will plenty of opportunities for finger-pointing in the direction of test manufacturers, proficiency testing programs, and ourselves as lab directors. However, with the advent of sensitive and specific molecular diagnostic methods, the good news is that better options for C. difficile testing are on the horizon.
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Unfortunately, efforts to improve turnaround time have come at the price of accuracy. In the past decade, C. difficile immunoassays have essentially overtaken the diagnostics market for C. difficile. Most laboratories in the United States now use toxin antigen detection systems, which despite improvements, still show poor correlation with the historical gold standard of toxigenic culture.
