Antimicrobial resistance and serotypes of Shigella isolates in Kigali, Rwanda (1983 to 1993): Increasing frequency of multiple resistance

Abstract

The serotype distribution and susceptibility to nine antibiotics was determined for 2491 Shigella isolates cultured in the medical laboratory of the Centre Hospitalier de Kigali, Rwanda, during 1983 to 1993. Overall, Shigella flexneri was the most frequent species, ranking before Shigella sonnei, Shigella boydii, and Shigella dysenteriae. However, the relative frequency of the different Shigella spp. showed an important variability over time. S. flexneri increased from 40% in 1983 to 68% of the isolates in 1993 whereas S. dysenteriae Type 1 decreased gradually from 30 to 0.5% of the isolates in 1992. After the outbreak of severe civil unrest, which caused the displacement of many people to the capital, a new epidemic of dysentery started in the Kigali area and S. dysenteriae Type 1 accounted again for 24% of the isolates in 1993. In 1983, resistance to tetracycline, streptomycin, and sulfonamides was common among the endemic Shigella spp. Resistance to chloramphenicol was observed in 17% (30/182) of the isolates. Only 10% were resistant to ampicillin and an equal proportion to trimethoprim, whereas 5% of the isolates showed resistance to both products. By 1993, 66% (195/295) of the isolates were resistant to chloramphenicol (for comparison with 1983, p < 0.001), 70% (207/295) to ampicillin ( p < 0.001), 67% to trimethoprim ( p < 0.001), and 58% had combined resistance to the latter two drugs ( p < 0.001). Resistance patterns differed strongly by species, S. flexneri being more frequently resistant than S. sonnei. In 1983, all S. dysenteriae Type 1 isolates were resistant to ampicillin, chloramphenicol, tetracycline, and sulfonamides. Trimethoprim resistance increased from 31% (25/80) in 1983 to 96% (26/27) of the isolates in 1986 ( p < 0.001). After the introduction of nalidixic acid as an alternative for trimethoprim-sulfamethoxazole, trimethoprim resistance decreased to 87%, during 1987 to 1992, and subsequently to 68% of the isolates in 1993. However, 20% of the isolates became resistant to nalidixic acid in 1993. Ampicillin and trimethoprim-sulfamethoxazole are no longer useful for the empirical treatment of shigellosis in Rwanda.