This is the first GBS carriage study to be performed in a rural South East Asian population and it adds to the scant knowledge of GBS carriage in this region and the developing world generally.
The GBS carriage rate in the pregnant women living in Maela camp for displaced persons is 12%. Two previous studies carried out in Thailand showed GBS carriage rates of 16% and 18% [21, 22]. The difference in these rates is not unexpected as the study participants were from different ethnic groups and geographic locations, with our study population being more reflective of a developing world country such as Myanmar.
The rate of culture positive GBS carriage was found to be lower than that detected by PCR. The PCR method used in this study has been compared to standard culture techniques and other PCR methods by Rallu et al. When compared to the scpB PCR, the cfb PCR was found to have a sensitivity of 75.3% and culture a sensitivity of 42.3% . Various hypotheses for this effect have been suggested: antibiotics in the lead up to the time of the swab or suppression of growth of GBS by enterococci present in vaginal and rectal flora. In addition, there may be difficulty in identifying GBS on culture due to overgrowth of Gram positive bacteria from the recto-vaginal swab or due to a light growth of GBS [23, 24].
Antibiotic susceptibility remains high in this population with most isolates retaining susceptibility to the macrolides despite reports of increasing erythromycin and clindamycin resistance in GBS carriage isolates in other regions . This most probably reflects the low use of these antibiotics in this population.
A large range of carried serotypes were identified, with only a small number (4.5%) being non typeable. All of the non typeable serotypes were on isolates identified by PCR not on culture positive isolates, which raises the possibility of false positive GBS cfb PCR results. However, the cT values for these specimens were well within the expected range. Four GBS culture positive isolates that were initially non typeable by latex agglutination were subsequently identified to be capsular genotype VI by PCR.
A recently published meta-analysis of geographical GBS serotype distribution of carriage isolates, showed that in Canada, North America and South America serotype Ia was the predominant serotype. In Europe, the Middle East, Africa, Australia and Asia serotype III predominated. Serotype II, which was the most common serotype found in this study, was not found to be a predominate serotype in any region .
There is very little published data on GBS carriage in Asia and in particular on the serotype distribution, however studies from Japan and Korea have described the GBS serotype distributions in their populations [27, 28]. In Korea the predominant serotype was serotype III (20.3%), followed by serotype Ia (12.1%). In the Japanese study serotype VIII was the most common serotype making up 35.6% of isolates. Another common serotype isolated in this study was serotype VI, which is rarely reported in carriage studies from other parts of the world. Interestingly this was the second most common isolate in our study. The frequency of isolation of this serotype was not significantly different to that in our study (24.6% vs 16.7% p = 0.3).
One of the strengths of the current study is that GBS serotyping was performed on both culture isolates and PCR positive isolates giving an accurate picture of serotype distribution in this population.
An ongoing study in the same population will define the incidence of early onset neonatal sepsis and the specific role of GBS, with the aim to combine the results of both studies in order to formulate a preventative strategy for GBS neonatal sepsis.