Emerging enteric fever due to switching biotype of Salmonella (paratyphi A) in Eastern Odisha

Background: Typhoid fever is classically caused by Salmonella enterica serotype typhi.Recently the frequency of isolation of S. paratyphi A (SPA) has been increased in comparison to S. typhi in Indian scenario. Aim: To observe the rate of isolation and antimicrobial susceptibility pattern of SPA from suspected enteric fever cases attending tertiary care centres of Eastern Orissa. Settings and Design: Retrospective study Materials and Methods: 1488 blood samples were collected during different duration of fever and cultured in BACTEC blood culture system and bottles showing signal for growth were subcultured and identified as Salmonella spp. by standard procedure and mini API (Biomeriux) and antimicrobial susceptibility by disc diffusion method. Statistical Analysis: Chi square test. Results: 167 Salmonella spp. were isolated including 83.8% Salmonella paratyphi A and 16.6% S. typhi. Among them 102 were males and 65 were females with mean age of 22.7 yrs. S. paratyphi A was the predominant spp. each year but during 2008 – 2011, there was a dramatic rise (significant P value- 0.034). Multidrug resistance was noticed in 10.2% of the isolates. 98% of S. paratyphi A were resistant to nalidixic acid and 41% to ciprofloxacin, but the MIC of ciprofloxacin was raised between 1-2 μgm/dl showing the relation between nalidixic acid resistance and raised MIC of ciprofloxacin. Conclusion: Nalidixic acid should be tested along with ciprofloxacin disc while testing for susceptibility and MIC of ciprofloxacin is mandatory before advocating therapy to prevent treatment failure.