The concurrent prevalence of chloramphenicol-sensitive and multi-drug resistant Salmonella typhi in Vellore, S. India.

A multidrug resistant (MDR) variety of Salmonella typhi emerged as the cause of epidemic typhoid fever in some Asian countries including India, during the late 1980s. We faced the epidemic from April 1990 to the first quarter of 1993. However, during this period we continued to isolate chloramphenicol sensitive (CS) S. typhi also. The relative prevalences showed that the frequency of CS variety was unaffected by the epidemic of MDR variety. This is an unusual epidemiological pattern, which indicates that there may have been factors which favoured the epidemic of the MDR variety but not the CS one.