Mohammad-Mehdi Soltan-Dallal PhD

Diarrhea is a major cause of mortality in 15 to 20 percent of the under 5-year-old children¹ and it contributes to approxi-mately 5 to 10 million cases of mortality in Asia, Africa and Latin America. Diarrhea is caused by a variety of infectious agents. Among the bacterial agents, the five most important are Shigella, Salmonella, Escherichia coli, Yersinia, and Campylobacter.

This study was conducted in cooperation with the local health center of Islamshahr (allied to Tehran University of Medical Sciences), South of Tehran, with the aim of obtaining etiological, epidemiological and demographic data on children with acute bacterial diarrhea.

During a one-year period (June 1998 to June 1999), a total of 1600 rectal swabs were collected from children less than 5 years of age presenting with acute diarrhea. Acute diarrhea was defined as illness less than 2 weeks duration.

The specimens were inoculated in Cary-Blair transport medium and immediately sent to the Microbiology Laboratory of the Public Health Faculty, Tehran University of Medical Sciences. Each specimen was examined microscopically and then cultured according to the standard method adopted from the WHO on Endo agar, Salmonella-Shigella (SS) agar, CIN agar and Campylobacter-selective agar.² For isolation of Salmonella, the specimens were incubated in selenite F medium for 12 hours before primary culture. For isolation of Yersinia, the cold enrichment method was used in which the specimens were incubated at 4˚ C for 2 weeks, inoculated in selective medium (CIN agar) and finally incubated at 25˚ C for 48 hours. For isolation of Campylobacter, regarding its microaerophilic conditions of growth, Gaspack system and anaerobic jar were used. After inoculation, the plates were incubated at 4˚ C for 48 hours, and the suspected colonies were identified. For isolation of Enteropathogenic E. coli (EPEC) and Shigella, without a non-specific process, rectal swabs were inoculated on Endo agar and SS agar. The suspected colonies were identified by anti-serum manufactured by DifCo, USA.

Table 1. Enteropathogenic bacteria isolated from children with diarrhea in Islamshahr.

From the 1600 rectal swabs analyzed, 235 (14.7%) revealed positive bacterial cultures. Table 1 shows the various enteropathogenic bacteria isolated from the specimens. Enteropathogenic E. coli was the most prevalent agent comprising 6.8% of all positive cultures. Shigella spp (3.4%) and Salmonella spp (2.9%) ranked second and third respectively.

The prevalence of various pathogens was different across age groups. Campylobacter spp were only met in children less than 2 years of age. While, two-thirds of EPEC (67%) and Yersinia (63.6%) and around one-third of Shigella (25.9%) and Salmonella (21.7%) infections occurred in children waged less than 2 years (Table 2).

Seasonal investigations showed that diarrhea due to EPEC, Shigella, Salmonella, and Campylobacter mostly occurred in the summer whereas diarrhea caused by Yersinia enterocolitica was prevalent in the spring (Figure 1).

Acute diarrhea is an important health problem in children as well as adults.³ This study showed that five bacterial agents i.e. E. coli, Shigella, Salmonella, Campylobacter and Yersinia play a major role in pediatric gastroenteritis in southern Tehran. The prevalence rate of bacterial diarrhea in our sample was 14.7%, whereas Naqvi in the USA⁷ and Germani⁸ in New Caledonia (tropical climate), reported a prevalence of 8.6% and 28% respectively.

The etiology of diarrhea varies according to geographic and climatic conditions. In contrast to the warm and tropical areas^4,5, in cold regions including Europe, Vibrio cholera, Aeromonas, Plesiomonas and Shigelloides are seldom isolated. The prevalence of psychrophilic bacteria such as Yersinia in intestinal infections is higher in the colder than the warmer climates.^6-8

The results of this study present a profile of various pathogens including Campylobacter and Yersinia, specifically the Y. intermedia and Y. fredriksenii among other intestinal pathogens in the region. Individuals and health services should be aware of this prevalence pattern and perform necessary medical interventions.

Table 2. Age distribution of 235 culture-positive children with gastrointestinal bacterial infections.

Figure 1. Isolation of gastrointestinal pathogens from children with diarrhea in different seasons.