Hospital based surveillance of childhood diarrhea in Port Blair

A hospital based surveillance of childhood diarrhea cases was started in 1994. The study is being conducted based at G.B. Pant Hospital, Port Blair. Pediatric patients with diarrhoeal diseases are being investigated for bacterial enteric pathogens. Stool samples/rectal swabs are collected from the patients and are processed to isolate bacterial pathogens. Isolated Shigella, Salmonella and E. coli are serotyped using commercially available antisera. Antibiotic sensitivity of the isolates is tested using disc diffusion technique.

Isolation rate of Shigella spp. During 1994—2003

Proportion of different shigella species among all shigella isolates

Till November 2003, a total of 2459 fecal samples have been processed. The commonest bacterial pathogen isolated was Shigella spp. A total of 237 Shigella isolates have been obtained so far. Isolation rate of Shigella varied between 4.2% to 27.9% (Fig. 1).  Isolation rate of Shigella shows two peaks, the first during 1995 and the second during 2003. These peaks might represent periodic outbreaks of shigellosis.

Proportion of each shigella species among all shigella isolates during each year is shown in figure 2. During most of the years, Sh. flexneri is the predominant species. However,  Sh. dysenteriae replaced Sh. flexneri as the predominant species in 1995. During the past three years, Sh. sonnei is accounting for a higher proportion of cases than it used to before. In 2001 and 2003, Sh. sonnei was the predominant infecting strain. The dominance of Sh. dysenteriae during 1995 occurred when there was an outbreak situation in the islands. The dominance of Sh. sonnei during the past  few years appears to be an unusual phenomenon. This might be an indication of an ongoing or impending outbreak due to this species. Monitoring the species composition of shigella isolates serves  helps to detect outbreaks at early stages.

Change in the antibiotic sensitivity pattern of Shigella isolates during 1994—1999

In 1994 all isolates were sensitive to nalidixic acid, norfloxacin, ciprofloxacin and gentamycin while resistant to ampicillin. About 80% of the isolates were resistant to cotrimoxazole and about 10% to furazolidone. Nalidixic acid resistance started appearing in 1995 and gentamycin resistance in 1996. The change in the antibiotic sensitivity pattern of the Shigella isolates during the period 1994—1999 is shown in fig 3.

All Shigella isolates continue to be resistant to ampicillin and most to co-trimoxazole. Increasing proportion of the isolates is becoming resistant to nalidixic acid. Gentamycin resistance reached a peak in 1998 and then declined. Norfloxacin and ciprofloxacin resistant strains have not yet been isolated. The continuous monitoring of the antibiotic resistance pattern of the isolates have helped to identify emergence of multiple drug resistant strains and to modify the treatment regimen accordingly.