Epidemiology of Shigellosis in Lagos, Nigeria: Trends in Antimicrobial Resistance
Iwalokun, B. A., Gbenle, G. O., Smith, S. I., Ogunledun, A., Akinsinde, K. A., Omonigbehin, E. A., Journal of Health Population and Nutrition
Shigellosis still remains a public-health problem in most developing countries where communities are ravaged by poverty, war, poor sanitation, personal hygiene, and water supplies (1). Epidemiologic reports show that about 140 million people suffer from shigellosis with estimated 600,000 deaths per year worldwide (2,3).
In Nigeria, shigellosis is still the major cause of dysentery in children aged 0-9 year(s), and many older children are hospitalized almost immediately after the onset of the disease (4). Although antibiotic therapy is important in the treatment of shigellosis in most endemic countries, antibiotics, including ampicillin, trimethoprim-sulphamethoxazole, and nalidixic acid, have been banned in the treatment of shigellosis in countries of Asia and sub-Saharan Africa (5,6). Furthermore, drugs, such as fluoroquinolones, azithromycin, and pivamdinocillin, have been found to be efficacious both in vitro and in vivo in the treatment of shigellosis in children and adults (7,8). These drugs have helped control and manage shigellosis in many countries (9).
In Nigeria, an active surveillance study on shigellosis was carried out over a decade ago (10). Since then, no studies were conducted to examine the status of drug resistance in shigellosis. This situation might have been responsible for the severity, prolonged illness, and high hospitalization rate of patients with shigellosis in Lagos recently (4). If this trend continues too long, the mortality rate due to shigellosis may rise in Lagos. Furthermore, there is a paucity of information on co-infection of shigellae with other pathogenic Enterobacteriaceae.
This study was, therefore, carried out to determine the antibiotic susceptibility profile of Shigella spp. and to determine the incidence of co-infection of shigellae with enteropathogenic Escherichia coli (EPEC).
MATERIALS AND METHODS
Patients and sample collection
During March 1999-February 2000, 1,020 stool samples were collected from diarrhoeal patients who sought treatments at the Massey Children's Hospital, Mainland Infectious Diseases Hospital, Central Medical Health Laboratory Services, Yaba, Lagos, and Randle Medical Health Centre, Lagos. These hospitals/clinics serve as referral centres for most communities and towns in Lagos metropolis. Patients included children, adults, and elderly people.
Fresh faeces of patients were collected into Cary-Blair tubes (10 mL per tube) and transported to Microbiology Laboratory of Nigerian Institute of Medical Research, Lagos, for immediate culture. The specimens were inoculated on MacConkey and Salmonella-Shigella agar. Colonies suspected to be shigellae were further subcultured on Simmon-citrate, motility-indole-urea and Kligler-iron agar. The Shigella isolates were speciated biochemically as outlined by Cowan (11). Colonies on MacConkey plates suspected to be E. coli were further tested for enteropathogenicity by slide and tube agglutination tests using E. coli polyvalent antisera A, B, and C (Biotec Laboratories, UK).
Antimicrobial susceptibility testing
Resistance patterns of the isolated Shigella strains to 12 antibiotics were determined by the agar-diffusion technique (12). Every inoculum was prepared by inoculating 5 mL of Mueller-Hinton broth with five colonies of 18-hour old pure Shigella culture followed by incubation in ambient air and at 37 °C for 16 hours. The resulting turbid culture was standardized to the turbidity of 0.5 McFarland (A^sub 625nm^=0.09) using 0.85% NaCl as the diluent. A sterile cotton swab was dipped into the standardized suspension, drained, and used for inoculating 25 mL of Mueller-Hinton agar in a 100-mm plate (Sterilin, UK). The inoculated plates were air-dried, and antibiotic disks from Oxoid (UK) and Mast Laboratories (Merseyside, UK) were mounted on them. The 12 antibiotics that were tested for susceptibility included: ampicillin, tetracycline, colistin sulphate, cotrimoxazole, cefotaxime, nitrofurantoin, nalidixic acid, streptomycin, ofloxacin, ciprofloxacin, chloramphenicol, and gentamicin. …