BMC Public Health 2009, 9:437 http://www.biomedcentral.com/1471-2458/9/437 Background Group B Streptococcus (GBS) is now recognized to be an important cause of maternal and neonatal morbidity and mortality in many parts of the world [1,2]. GBS infections tend to occur more commonly among adults than in neonates, but the overall mortality is higher in neonates [3]. Risk of disease is greater in pregnant women than in men and non-pregnant women. At birth, infants who are born to colonized mothers may also become colonised on their mucosal surfaces such as oral, nasopharynx, vaginal and anal mucosa and skin [4]. Approximately 60% of infants born to colonised mother become colonised with their mother's organisms [3]. The likelihood of neonatal colonisation at birth is higher if the mother is heavily col- onised [3]. GBS infection is the leading cause of perinatal bacterial infection [5], being commonly responsible for septicemia, meningitis and pneumonia in neonates. However, the burden of perinatal GBS disease varies between countries. Intrapartum antimicrobial prophylaxis to GBS carriers has been reported to be effective in reducing GBS disease. Pre- vention guidelines for perinatal GBS disease were issued by Centers for Disease Control and Prevention (CDC) in 1996, and revised in 2002 [6,7]. Since its introduction, the incidence of early-onset neonatal infections has decreased by 62% [7]. In Tanzania, as is the case in several other sub-Saharan countries in Africa, the rate of GBS colonisation among pregnant women and neonates has not been studied and therefore to date no strategies have been formulated to prevent neonatal GBS infection in the country. Thus the aims of this study was to determine the prevalence and risk factors of maternal and neonatal colonisation with GBS at Muhumbili National Hospital (MNH), Dar es Salaam Tanzania in order to generate local data that will inform the development of rational interventions for GBS infection and disease. Methods Study design and setting This was a hospital based cross-sectional study conducted at Muhimbili National Hospital (MNH), Dar es Salaam, Tanzania between October 2008 and March 2009. MNH is a tertiary facility which handles referrals from periph- eral and upcountry hospitals. Study population The study included 300 third trimester pregnant women (from 37 weeks of gestation) attending the antenatal clin- ics at MNH for routine antenatal visits and their neonates (180) delivered at the MNH labor ward. Sample size was calculated from the following formula n = z2p (100-p)/e2 where p, in the absence of local data, was taken as the median prevalence of GBS carriage among pregnant women in African countries (16%) [8,9]. All consenting mothers with gestation age ≥ 37 weeks were included. Par- ticipants with history of using antibiotic(s) within two weeks prior to recruitment were excluded from the study. Data collection Data was collected after obtaining written informed con- sent using a standard structured questionnaire designed to obtain social demographic data and other relevant infor- mation such as maternal age, gestational age, previous obstetric history, history of current pregnancy, parity, marital status, mode of delivery, administration of antibi- otics during labor and neonate's birth weight. Pregnant women were interviewed at 37 weeks of gestation, during labour and after delivery. Specimen collection and transport High vaginal and rectal swabs were collected at 37 weeks of gestation using sterile swab stick. In addition, umbilical swabs, ear canal and nasal swabs were collected from neonates within one hour after delivery. The swabs were inoculated directly into Todd Hewitt Broth (Oxoid Ltd) and transported to the central pathology laboratory of the MNH for processing within 2 hours of collection. About three millilitres of venous blood were drawn aseptically into sterile vacutainer tubes (BD NJ USA) without antico- agulant for detection of HIV antibodies and in EDTA (BD NJ USA) vacutainer tubes for quantification of CD4+T lymphocytes counts. Laboratory Procedures The swabs were inoculated in Todd-Hewitt broth (Oxoid Ltd) containing nalidixic acid (15 mg/L) and gentamicin (8 mg/L) and incubated at 37°C in 5% Co2 for 24 h. Sub- cultures were performed in 5% sheep blood agar for isola- tion of GBS. Broth cultures showing no visible turbidity after overnight incubation were further re-incubated and then sub cultured after 48 hours on sheep blood agar. Pre- sumptive identification of GBS was made by traditional physiological and biochemical methods. These included Gram stain, catalase reaction, hemolytic activity on sheep blood agar plates, hippurate and CAMP tests. Confirma- tive identification of Group B Streptococcus was done using Streptex- agglutination test (Remel Europe Ltd). Finally, antimicrobial susceptibility of all GBS isolates was determined by Kirby-Bauer disk diffusion method accord- ing to Clinical Laboratory Standard Institute (formerly NCCLS). The antimicrobials included; penicillin G (10 U), ampicillin (10 μg), clindamycin (2 μg.), erythromycin (15 μg), vancomycin (30 μg), ciprofloxacin (5 μg), ceftri- axone (30 μg) and co-trimoxazole 25 μg. S. agalactiae ATCC 27956 was used as a control organism. Page 2 of 7 (page number not for citation purposes)