Epidemiology of shigellosis in Lagos, Nigeria: Trends in antimicrobial resistance

Antimicrobial susceptibility of Shigella spp. and Escherichia coli, isolate d from diarrhoeal patients in Lagos, was studied from March 1999 to Februar y 2000. Four hundred fifty-nine isolates were identified as shigellae (62) and E. coli (397). Shigella flexneri, S. dysenteriae, S. boydii, and S. son nei accounted, respectively, for 51.6%, 17.7%, 17.7%, and 13% of the total number of shigellae isolated. Eleven cases of shigellosis occurred in the a ge group of 0-9 years, 22 cases in the age group of 10-19 years, and 29 cas es in the age group of greater than or equal to 20 years. Of the 397 E. col i isolates, 11 were enteropathogenic E. coli (EPEC), and 7 of these strains were isolated with shigellae from stools of patients aged 0-9 year(s) (71. 4%) and 10-19 years (28.6%). Over 70% of the Shigella isolates were resista nt to two or more drugs, including ampicillin and tetracycline. Twenty-one distinct multidrug resistance patterns were observed in these isolates. Dur ing 1990-2000, resistance to ampicillin increased from 70% to 90%, co-trimo xazole from 77% to 85%, chloramphenicol from 71% to 77%, streptomycin from 71% to 79%, and nalidixic acid from 0% to 11.3%. Resistance to tetracycline decreased from 89% to 79% but with MIC50 and MIC90 values outside the susc eptible range. While resistance to ciprofloxacin and ofloxacin remained nil with MIC50 and MIC90 values of 0.008 and 0.0016 mug/mL respectively. The r esults of this study revealed the endemicity of shigellosis with S. flexner i as the predominant serogroup in Lagos. Children and young adults were at a higher risk of severe shigellosis. The results also suggest that ampicill in, tetracycline, co-trimoxazole, and streptomycin should not be used as th e first-line drugs in the treatment of shigellosis. Nalidixic acid should s till be selectively used for treatment, while ciprofloxacin and ofloxacin c an be ideal alternatives.