EPIDEMIC TYPHOID IN CHILE - ANALYSIS BY MOLECULAR AND CONVENTIONAL METHODS OF SALMONELLA-TYPHI STRAIN DIVERSITY IN EPIDEMIC (1977 AND 1981)AND NONEPIDEMIC (1990) YEARS

From 1977 to 1986, Chile experienced an important typhoid fever epidem ic, despite statistics that indicated apparently improving levels of s anitation of drinking water and sewage disposal. The lack of antibioti c resistance among the Salmonella typhi strains isolated during this p eriod, the mild clinical presentation of the disease, and the initiall y low level of efficacy of the S. typhi Ty21a vaccine in the populatio n exposed to the epidemic suggested that this epidemic might have resu lted from the dissemination of S. typhi strains with unique characteri stics. To investigate this hypothesis, we used conventional methods (b acteriophage typing and biotyping) and molecular methods (restriction fragment length polymorphism analysis, ribotyping, IS200 typing, and P CR amplification of the fliC-d gene) to study a population of 149 S. t yphi isolates during 1977, 1981, and 1990, the Sears that included per iods with low (when the disease was endemic) and high (when the diseas e was epidemic) morbidities. Our results indicate that these S. typhi isolates in Chile represent a number of highly diverse variants of the clone of S. typhi with a worldwide distribution described by Selander et al. (R. K. Selander, P. Beltran, N. H. Smith, R. Helmuth, F. A. Ru bin, D. J. Kopecko, K. Ferris, B. D. Tall, A. Cravioto, and J. M. Muss er, Infect. Immun. 55:2262-2275, 1990). For example, we detected 26 Ps tI and 10 ClaI ribotypes among 47 and 16 S. typhi strains belonging to this clone, respectively. These results suggest that the Chilean epid emic nas probably produced by multiple sources of infection because of deficient sanitary conditions. These findings illustrate the usefulne ss of molecular methods for characterizing the potential causes of the typhoid epidemics and the possible routes of transmission of S. typhi strains in typhoid epidemics.