Current status of drug resistance & phage types of Salmonella typhi in India

A total of 11391 strains of S. typhi were received at the National Salmonella Phage Typing Centre at New Delhi during January 1990- August 1992, from various regions of India. Of these, 39.7 per cent were from north India, 37.5 per cent from central India and 22.8 per cent from south India. 64.5 per cent of S. typhi were found to be multidrug resistant (MDR), maximum resistance being observed in 1991 (71.6%) while it was least in 1990 (50.05%). There was a slight decline in the percentage of MDR strains in 1992. Region-wise analysis of the resistant strains showed maximum number in central India (71.32%), whereas it was least in the south (55.2%); 62.34 per cent of strains received from north India were MDR. Irrespective of the year or region, the predominant resistance pattern remained AMCSXTTE. The commonest phage type was E1, followed by 0 and A. This pattern was also seen in the MDR S. typhi. Certain degraded Vi strains, untypable Vi strains and Vi negative strains were also multidrug-resistant. An important change observed in this study was that a small number of strains belonging to phage types C1, K1, 28, 40, 41 and 42 which were always sensitive earlier, had developed multidrug resistance. Small outbreaks due to one phage type (e.g., 28 and 51) were short lived and subsided spontaneously. More diversity of phage types was observed in north India as compared to central and south India.