The number of pregnant women infected with bacteria that can cause life-threatening infections in their babies has increased dramatically since the 1990s, a Chinese University study shows. The prevalence of Group B streptococcus (GBS) among pregnant women was only 0.8 per cent in the early 1990s, but had risen to 10.4 per cent by 2002, according to a paper published in the latest issue of the Hong Kong Medical Journal. Professional women were also more prone to infection, although the reason for this was unknown. Professor Ng Pak-cheung of the university's paediatrics department, who worked on the paper, said GBS was the most common cause of infection among newborns. If the bacteria entered the lungs, it could cause pneumonia, or meningitis if it entered the blood stream, Ng said. One to three babies died in Hong Kong every year from GBS. Babies were at their most vulnerable during birth, when the mother's water broke, as the bacteria lives in the vagina, according to Ng. The bacteria is harmless to the mothers. A total of 1,002 pregnant women, whose average age was 30, were asked to take part in the study between January and May 2002, when they went for antenatal check-ups at Prince of Wales Hospital in Sha Tin. Of them, 104 were infected with the bacteria, the study showed. Prevalence of the virus varied depending on women's working lives. One in 10 housewives had the bacteria, 21 per cent of professionals and 5 per cent of blue-collar workers. 'The significantly higher GBS carrier rate in professionals was unexpected, as in previous studies GBS carriage was associated with lower socio-economic status,' the researchers wrote. Whether this difference was because of lifestyle, such as sexual behaviour, needed further investigation, they said. The study also looked at 952 of the 1,002 women after they gave birth. No significant relationship was found between GBS infection and premature birth, despite there being a proven link. Of the babies born, 12 developed an infection, although three of the mothers had tested negative for GBS. Researchers said that although it was hard to predict which babies were at risk of infection, Hong Kong needed to deal with the issue and come up with a prevention strategy. Ng said a possible method was to give pregnant women antibiotics before they gave birth to ensure the drug was passed onto the baby, although this would not work for mothers allergic to antibiotics. Prenatal GBS testing was common in Western countries but not in Hong Kong, Ng said.