GROUP B STREPTOCCAL INFECTIONS IN IBADAN

Abstract

This present study on group B streptococcal (GBS) diseases was carried out between 1977 and 1982 in Ibadan, the largest indigenous Black African city, and capital of Oyo State of Nigeria, with an estimated population of two million. Patients were those attending the University College Hospital, Adeoyo State Hospital and Jericho Maternity Hospital, the largest three government owned hospitals serving the whole population of Ibadan and the surrounding districts. Group B streptococcus (Streptococcus agalactiae) has now been established as a leading cause of neonatal sepsis in temperate countries, although it was previously recognized only as a major pathogen among the bovidae. The objectives of this study were to establish the types of human infections caused by this organism in Ibadan, a. tropical African city. It was also intended to determine the extent of the problem posed by this organism which had not previously been reported in Nigeria. Also by studying the factors that could contribute to the transmission and the development of infection and by performing antibiotics sensitivity testing on strains it was intended to formulate a comprehensive control policy for GBS infections in Nigeria.

Todd Hewitt broth containing 8mg/L gentamicin was used as an enrichment medium for the primary isolation of the organism. The ability of Streptococcus agalactiae to produce an orange pigment under anaerobic conditions on Columbia and Islam agar plates was used for a quick presumptive identification of the organism; while its gram reaction, its ability to hydrolyse sodium hippurate and its inability to hydrolise aecsculin were used as confirmatory tests. These were further confirmed by streptococcal grouping using the slide co-agglutination technique. A total of 1,038 patients were screened for colonization by the organism. Five hundred and eighty-eight (56.6%)of the patients were females of child bearing age; 150 (14.5%) were adult males and 300 (20.9%) were newborn babies of both sexes. An average vaginal colonization rate of 10.5 per cent was obtained for the women of child bearing age. Among 150 antenatal patients tested, 29(19.3%) were colonized. Colonisation rates among 236 pregnant women in labour and 200 female patients attending the clinic for the treatment of Sexually Transmitted Diseases (STD) were 17.6 and 19 per cent respectively. The differences in vaginal colonization rates among the various groups of female patients were not statistically significant (P>0.05). There was no significant association between genital carriage of GBS and STD among the female patients: genital carriage was generally associated with females, whether they had STD (P<0.01) or not (P< 0.01). There was however a strong association between genital GBS carriage and STD among the male patients (P<0.05) but this could not be linked with any particular STD. Using the external auditory meatus as an indicator site of superficial neonatal GBS colonization, it was found that 4.5 per cent of the 300 newborns screened in the hospitals were colonized by this organism. All serotypes of GBS were encountered: the commonest being types III (56.1%), Ic (14.4%) and X (11.4%). Type Ia was very rare indeed. There was a high incidence of R. (43.9%) and X (12.1%) antigens, being associated especially with types II and III strains. This high incidence of R and X strains were not, however, associated with zoonotic transmission of the organism. Both neonatal aid adult GBS infections were encountered during the course of this study. The early onset and the late onset types of neonatal sepsis were also encountered. Three newborns with the early syndrome were described and they all presented with septicaemia within the first 24 hours of birth. The predisposing factors were prematurity, premature rupture of the membranes, maternal fever and low birth-weight. They were caused by types Ic and II organisms. The patient presented with meningitis in association with epidural effusion at the age of four weeks. It was due to the type III organism. All the neonates responded favourably to systole treatment with gentamicin and ampicillin. Adult GBS infections were encountered only among females who presented with a somewhat bimodal age distribution. There was a younger group of patients with a mean age of 27 years presenting with urogenital symptoms mostly following premature rupture of the membranes, prolonged labour and surgery; and a 50-year old patient presenting with multiple skin abscesses complicating diabetes mellitus. One of the infecting strains in this study was the type X organ is. There was no mortality among the patients described. Using the Modified Stoke's Method of antibiotics sensitivity testing, it was shown that all the strains were sensitive to penicillin G, cefotaxime, chloramphenicol and erythromycin but 96.7 per cent were resistant to tetracycline. The minimum inhibitory concentrations (MIC) of penicillin G was determined for the GBS strains as this was the usual antibiotic used for treating infections caused by them. 95.6 percent had an MIC of 0.1 iu/ml; 3.2 per cent an MIC of 0.5 iu/nl and 1.2 per cent an MIC of iu/ml. The MIC results corroborate the results of sensitivity testing using the Modified Stokes Method, thus explaining the favourable clinical response of the patients who were all treated with penicillin in combination with other antibiotics. This study therefore showed that there were only occasional cases of GBS sepsis in Ibadan among neonates and also among adults. The female genital tract was confirmed to be a major colonized site by this organise with an average carrier rate of 16 per cent. The risk of developing neonatal infection as reported in literature is about one per 100 colonized infants. From this figure a neonatal infection rate of 2 - 4 cases per 1000 births was expected for Ibadan. However from the result of collaborative studies no neonatal cases were recorded during a 4-month period; and there were only cases of neonatal sepsis reported during a 2 year period at the University College hospital Ibadan; this was an incidence of 0.4 cases per 1000 births. A possible explanation for the low incidence of neonatal GBS sepsis in this report is the preponderance of the type III organism in the female vagina. Type III GBS possesses immunogenic antigens which could evoke the development of maternal antibodies of the IgG type that would be protective for newborn babies. Another possible explanation is the fact that other pyogenic organisms including the enterobacterioceae predominate in infections in the Tropics, thus competing with GBS. An increased incidence of GBS infections was associated with a decline in the incidence of infection caused by the enterobacterioceae in the United States of America. Potentially therefore, the latter could pose a major health problem in future when infections due to the other organisms have been controlled. As a result of the foregoing, a comprehensive control policy for an outbreak of GBS disease was formulated which included treatment of cases and prophylaxis of neonatal infections.