Strengths and Limitations
The high rate of vertical transmission found in our study differs from the results of previous studies that reported the vertical transmission of MRSA from mothers to their neonates13,15,18-22. In these reports, the vertical transmission rate of MRSA was as high as 10%, and no study reported as high as 40% observed in this study. This inconsistent observation may in part be due to small sample size in our study with only nine pregnant women detecting MRSA in the vagina. Another possible reason for the high rate of vertical MRSA transmission in our study may be that since the cultures are taken immediately after delivery, a large amount of maternal vaginal secretions can remain and lead to a high detection rate. However, this should be included within vertical transmission and not be considered as a false-positive result. Additionally, the vertical transmission rate of GBS by delivery is reported to be approximately 40%23,24. Taking those factors into account, the vertical transmission rate of 44.4% (4/9 pairs) for vaginal MRSA may be reasonable.
Although we performed further stratified analyses to determine other factors that would increase the vertical transmission rate, we did not detect any factors because of the low prevalence rate of vaginal MRSA carriers and the limited sample size. Further studies with larger sample sizes are needed to detect factors that could affect the vertical transmission rate of MRSA.