Emergence of multidrug-resistant Shigella dysenteriae type 1 causing sporadic outbreak in and around Kolkata, India.

Abstract

Sir, Shigella dysenteriae type 1 is known to cause epidemics of bacillary dysentery worldwide. In 1984, an extensive outbreak of bacillary dysentery swept through several districts of West Bengal, including the state capital Kolkata, and subsequently, spread to other parts of India (1). Multidrug-resistant S. dysenteriae type 1 was identified as the sole aetiological agent in this outbreak. In the later period, the number of shigellosis cases gradually declined. During the last five years, the number of dysentery cases admitted to the Infectious Diseases Hospital, Kolkata (which serves as a referral centre for all types of diarrhoea cases in Kolkata and suburbs) was relatively low. The isolation rate of Shigella species varied from 1% to 1.3%, and S. flexneri was the commonest serotype identified (2). However, continuous surveillance of diarrhoeal cases at the Infectious Diseases Hospital, Kolkata, revealed a sudden increase in acute bloody diarrhoea cases since July 2002. During 1 July-15 September 2002, stool samples were collected from 100 patients (both children and adults) suffering from acute bloody diarrhoea and were screened for the entire gamut of enteric pathogens following standard microbiological techniques (3). Among these 100 patients, Shigella species was isolated as the sole pathogen from 39 patients. S. dysenteriae type 1 was the commonest serotype (34 strains), followed by S. flexneri (4 strains), and S. sonnei (1 strain). Besides bloody diarrhoea, the other clinical manifestations of 39 bacteriologically-positive cases included severe abdominal pain (85.7%), fever ranging from 37.2[degrees]C to 38.3[degrees]C (63.8%), tenesmus (20.4%), and moderate dehydration (87.8%); only four cases showed signs of severe dehydration requiring administration of intravenous fluid. The table shows the age distribution of 39 bacteriologically culture-positive cases of shigellosis. When enriched stool samples were subjected to polymerase chain reaction (PCR) for detection of ipaH (invasive plasmid antigen H) gene using published primers (4), 49 samples (49%) were positive by PCR test, which included all 39 bacteriologically-confirmed cases. No other enteropathogens, such as Vibrio parahaemolyticus, Campylobacter species, and enterohaemorrhagic Escherichia coli, could be detected from the cases. During this sporadic outbreak of dysentery, clinicians of the Infectious Diseases Hospital were using conventional anti-Shigella drugs--norfloxacin or ciprofloxacin (the fluoroquinolone derivatives)--for treatment of the patients. The clinical response was, however, very poor. Subsequently, in vitro antimicrobial susceptibility test revealed that the strains of S. dysenteriae type 1 were resistant to ampicillin (100%), tetracycline (100%), nalidixic acid (100%), norfloxacin (100%), and ciprofloxacin (100%) but were susceptible to ofloxacin (100%), ceftriaxone (100%), gentamicin (100%), amikacin (100%), cefotaxime (100%), cefuroxime (100%), cefoxitin (100%), and ceftazidime (100%). Surprisingly, strains of S. flexneri and S. sonnei were susceptible to norfloxacin, ciprofloxacin, ofloxacin, and other newer generations of antibiotics. This finding prompted the physicians to switch over to oral ofloxacin (another fluoroquinolone derivative) for treatment with a total dose of 7.5 mg/kg.day in two divided doses for five days. The majority of the Shigella-positive cases responded well to ofloxacin; abdominal colic and tenesmus subsided within an average of 72 hours; and return of normal stool character was observed within 96 hours. …