Fecal Leukocytes and Erythrocytes in Shigella Infections

We evaluated the usefulness of enumeration of fecal leukocytes and erythrocytes in making an early diagnosis of Shigella infection, where Shigella is a leading cause of invasive diarrhea. Stool specimens from 561 invasive diarrhea patients were submitted for microscopic examination. A presumptive diagnosis of shigellosis based on microscopic examination was made in 389 of them; 227 had stool cultures positive for Shigella spp (Shigella patients). One hundred sixty-two patients with no detectable Shigella infection (non-Shigella invasive diarrhea cases) served as a comparison group. Two hundred twenty-seven randomly selected Shigella patients and 227 non-Shigella infectious diarrhea cases from the surveillance system database of the hospital constituted another group for comparative evaluation. The stool specimens of the patients were examined under the microscope, and isolation, biochemical characterization and serotyping of Shigella were performed. In comparison with non-Shigella invasive diarrhea cases, the presence of >50 WBC/hpf in association with any number of RBC in the fecal sample had a modest sensitivity of 67%, specificity of 59%, positive predictive value of 70%, negative predictive value of 56%, accuracy of 64%, and positive likelihood ratio of 1.6 in predicting shigellosis. Comparison between Shigella and non-Shigella infectious diarrhea patients revealed the presence of >20 WBC/hpf was a less accurate predictor of shigellosis (sensitivity 51%, specificity 88%, positive predictive value 81%, negative predictive value 64%, accuracy 69%, and positive likelihood ratio 4.1). Direct microscopical examination of stool specimens for the presence of WBC and RBC may facilitate the early diagnosis of shigellosis, and may be a cheap alternative to stool culture in this setting. million deaths (Kotloff et al, 1999). Effective antimicrobial therapy for shigellosis shortens the duration of illness, hastens clinical recovery, lessens severity of the disease, and may prevent the development of life-threatening complications, particularly those which occur later in the course of il lness (Salam and Bennish, 1991). Delay in recognizing Shigella infection may also result in delay in initiating effective antimicrobial therapy. Shigella is known to penetrate the large gut mucosa, where it initiates an intense acute inflammatory response resulting in fecal excretion of leukocytes and erythrocytes (Mathan and Mathan, 1991). The possible value of fecal quantitative and qualitative cell counts in diSOUTHEAST ASIAN J TROP MED PUBLIC HEALTH 748 Vol 37 No. 4 July 2006 agnosing specific bacteria has been reported. Several authors (Harris et al, 1972; Pierce et al, 1974; Pickering et al, 1977; Korzeniowski et al, 1979; Stoll et al, 1983; Hossain and Albert, 1991) have emphasized the presence of leukocytes on microscopic examination of the stool as a rapid, reliable, and inexpensive method for distinguishing diarrhea due to invasive microbial infection (Shigella, Salmonella or Campylobacter) from other causes of diarrhea, such as those due to viruses, parasites or bacterial toxins (Harris et al, 1972; Pierce et al, 1974; Pickering et al, 1977; Korzeniowski et al, 1979; Stoll et al, 1983; Hossain and Albert, 1991). Investigators in Bangladesh (Stoll et al, 1983; Hossain and Albert, 1991; Bardhan et al, 2000) demonstrated the importance of the presence of both WBC and RBC in stool as a simple and inexpensive method for diagnosing shigellosis or invasive diarrhea in Bangladesh. Changes in the proportions of various Shigella serogroups over time has been observed in Bangladesh (Stoll et al, 1982a,b; Hossain et al, 1998). In recent years, several new subserotypes of Shigella have been identified in Bangladesh and in other developing countries (Simmons and Romanowska, 1987; Carlin et al, 1989; Talukder et al, 2001). We reassessed the comparative diagnostic values of fecal WBC and RBC in differentiating Shigella from non-Shigella invasive diarrhea cases and Shigella symptomatic infections from other nonShigella infectious diarrhea cases, to serve as a rapid screening test to identify patients whose stool should be cultured for isolation of Shigella and to identify patients who would benefit from antimicrobial therapy. MATERIALS AND METHODS