Prospective Case-Control Study of the Association between Common Enteric Protozoal Parasites and Diarrhea in Bangladesh

Background. The parasitic causes of diarrhea have historically been identified by use of microscopy; however, the use of this technique does not allow one to distinguish between subspecies or genotypes of parasites. Our objective was to determine, by use of modern diagnostic methods, the proportion of diarrhea cases in Bangladesh attributable to Cryptosporidium hominis, Cryptosporidium parvum, Entamoeba histolytica, and Giardia lamblia assemblages A and B. Methods. A prospective case-control study was performed involving 3646 case patients (both children and adults) who presented with diarrhea to the Dhaka hospital of the International Centre for Diarrhoeal Disease Research, Bangladesh, and 2575 control subjects with asymptomatic infection. Parasitic infection was detected by use of a stool parasite antigen test, and the parasite load and the species and/or genotypes were determined by use of polymerase chain reaction (PCR). Results. Cryptosporidium species and E. histolytica were more prevalent in patients with acute diarrhea than in healthy control subjects, for all ages (2.1% vs. 1.4%; P = .039) and, specifically, for those 0-12 months of age (2.2% vs. 0.4%; P = .009). G. lamblia assemblage A was also more prevalent in case patients with diarrhea than in healthy control subjects (20% vs. 5%; P <.001). For case patients with diarrhea, the parasite load in feces, as measured by quantitative real-time PCR cycle threshold, was not higher that that for control subjects with asymptomatic infection. Case patients with diarrhea and cryptosporidiosis were less likely to have abdominal pain, compared with control subjects (15% vs. 37%; P <.001); case patients with amebiasis more likely to have visible blood in stool, compared with control subjects (8% vs. 1.6%; P <.001); and case patients with giardiasis more likely to be dehydrated, compared with control subjects (81% vs. 71%; P = .001). Conclusion. E. histolytica, C. hominis, C. parvum, and G. lamblia assemblage A infections are important causes of diarrheal illness in Bangladesh.