Revisiting Bacterial Gastroenteritis: Issues, Possible Approaches, and an Ever-Expanding List of Etiologic Agents, Part II

Isolation of bacteria from stool is difficult, even when looking only for Salmonella, Shigella, and Campylobacter jejuni/Campylobacter coli or other known diarrheal pathogens. Many factors compromise the process, ranging from host factors, the time that the stool specimen is collected in relation to the onset of symptoms, the quality of the specimen, and the number of isolation and enrichment media used to the experience and skill of the microbiologist. Either in combination or alone, any of these factors can contribute to a suboptimal stool report. Diarrhea can also be attributed to non-infectious causes. So, when and why should the laboratory, often already overburdened, be tasked with the prospect of looking for putative diarrheal pathogens? We have tried to provide a convincing argument here that (i) for patients with severe diarrheal disease, whether it is acute or persistent, or (ii) for outbreaks of diarrhea where no etiologic agent is found, other putative bacterial pathogens may be responsible. Laboratories often come upon these agents routinely in stool specimens without ever suspecting that, in the absence of conventional pathogens, these organisms may be responsible for the patient's disease. Part I of this article discussed the rationale for testing diarrheal stool specimens, along with a brief introduction to various putative bacterial diarrheal agents. Part II of this review expands on the “when and how” of isolation of uncommon organisms responsible for enteric infection. We hope that this review provides incentive and encouragement for clinical laboratories, so that when circumstances allow, they may choose to pursue the isolation and identification of these organisms. Isolates could then be forwarded to a reference laboratory for definitive identification and detection of virulence characteristics.