An overall colonisation rate of 64% was obtained among the pregnant women attending antenatal clinic and labour ward of LUTH between December 2010 and October 2011 because I used PCR in addition to culture. The rate obtained by culture only was much lower and falls in the range of carriage rates (6.6 to 20%) reported from previous studies in pregnant Nigerian women.12,25-27 This shows how insensitive culture is for isolating GBS. Colonisation rates by GBS vary widely from 4 to 40% globally47,59,116-117 and these rates have been shown to be affected by many factors including source of samples i.e. vaginal or rectovaginal samples, gestational age at which sample is taken, laboratory experience and method of detection36,57,118-122 However, despite this high colonisation rate, the mother-to-baby transmission rate was low, only 6.8%. This was much lower to the 28% transmission rate obtained from a similar study in the hospital in 1988.52 These rates however are lower than rates from some western countries which range from 35% to 70%.53-54 Though the reason for this is not clear, in this study, GBS is still much susceptible to penicillin and with high rates of antibiotic misuse and abuse in Nigeria129 it is possible that this high maternal carriage of GBS may not translate to corresponding high transmission rates to their newborns. In addition, none of the colonised babies on follow up developed invasive disease. This finding confirms earlier findings which show that GBS is not a common cause of neonatal infection in Nigeria.12,25,52 In fact, Staphylococcus aureus and Klebsiella pneumoniae are the most common cause of neonatal sepsis in Nigeria.123-126 In recent times though, studies from Kenya,17,127 South Africa,18,20 Zimbabwe16,59 and Malawi19 suggest that GBS is emerging as an important cause of neonatal sepsis in Africa. However, these trends are not shown in Nigeria; thus far there is 49 DR CHARLES J. ELIKWU (Studies On Group B Streptococci Carriage In Pregnant Women in A Tertiary Institution In Lagos Nigeria) MAY 2012 Department Of Medical Microbiology And Parasitology, LUTH Lagos only one study from South-Eastern Nigeria and it reported only one single case of GBS neonatal sepsis from 33 septicaemic neonates of 138 that was screened.125 Unlike in the 1988 study in this hospital in which the predominant strain isolated was serotype III (20/36; 55%) from both mothers and babies52 but now there were a variety of colonising serotypes and they were similar to serotypes circulating globally. In this study, serotypes Ia and III were the predominant serotypes and were found in 44.7% of mothers with serotypes Ib, V and II making up the rest in contrast to what was found in the babies in whom serotype II was predominant accounting for 71.4% of all isolates. This could suggest a changing epidemiology or better laboratory typing methods because of the molecular typing methods used as opposed to serotyping by antisera raised in rabbits in 1988.52 This range of serotypes is similar to those found across the African subcontinent though the most common serotypes may differ from country to country. 13, 19, 59 The ST-17 lineage was also determined to identify the ST-17 clone which has been recognized as a hyper virulent strain especially with reference to serotype III among invasive strains in newborns. Only 4 of 7 isolates belong to this clone which comprised two strains of serotype II and one strain each of serotype Ia and III. GBS serotype II-ST-17 strains are rarely associated with invasive disease in neonates unlike their serotype III-ST-17 counterparts. The reason for this is that relative to serotype III strains, other serotypes showed reduced invasive potentia.20,128 The usual risk factors such as poor socio-economic status of women, maternal age, parity, gestational age at sampling or bacteria vaginosis were not significantly associated with GBS carriage rate however there was a significant association between GBS carriage and coital frequency of twice a week or more (X2 = 2.2; p value < 0.05). This finding raises a number of questions? Is GBS sexually transmitted? Or is there an association between GBS 50 DR CHARLES J. ELIKWU (Studies On Group B Streptococci Carriage In Pregnant Women in A Tertiary Institution In Lagos Nigeria) MAY 2012 Department Of Medical Microbiology And Parasitology, LUTH Lagos vaginal colonization and an elevated pH of vaginal environment (since semen is alkaline). The possible association of raised pH as a risk factor was not supported by the evidence since there was no significant association with bacterial vaginosis. The possibility that GBS may be transmitted sexually is novel and will require further study. Also, other factors that increases the risk for a baby being colonised and getting disease, such as gestational age <37 completed weeks, prolonged rupture of membrane and intra-amniotic infection76-81 were absent in all the mothers studied except in three women with GBS carriage who had intrapartum fever. However none of their babies developed GBS invasive disease. All GBS isolated in this study were susceptible to penicillin G, the recommended antibiotic for intrapartum antibiotic prophylaxis49-50 though 6.5% were resistant to erythromycin. This is unexpected because of the high rates of antibiotic misuse and abuse in Nigeria129 especially as high rates of resistance of up to 35% against erythromycin have been reported from other parts of the world.60 The mechanism of resistance was found to be as a result of the presence of the genes that expresses macrolide efflux and erythromycin methylases in the resistant isolates. This was also recorded in this stud