Dr Wong Ka-hing, senior medical officer at the Department of Health's special preventive programme, said a study by his unit found that HIV-infected pregnant women who took anti-HIV drugs could reduce the chances of infecting their babies from 40 per cent to five per cent.

The same study also found that babies were 15 times more likely to be infected with HIV if their mothers' condition was not diagnosed before giving birth.

Dr Wong announced the results of the study while providing an Aids progress report for 2000.

There were 183 cases of HIV infections reported last year. Of these, 139 were men and 44 were women, with the ratio shrinking in recent years. Two are babies born to infected mothers. So far, official figures show 12 babies have been infected by their mothers since the first case in 1994. Five of them have developed Aids.

The study released yesterday involved 28 mothers who gave birth between 1993 and 2000. It found that of 14 mothers whose HIV status was known before childbirth, 10 babies born tested negative and two positive. In the other group of 14 mothers whose HIV status was not known, nine of the babies were HIV infected and two were negative.

HIV is transmitted from mothers to babies during pregnancy, delivery and breast-feeding.

The "cocktail of drugs" should start to be taken by expectant mothers after 24 weeks of pregnancy, continue until delivery and then be given to newborn babies for six weeks.

In the study, two babies were born positive despite intervention because one mother defaulted on the course of treatment, while a second mother was about to deliver when she went for HIV tests, Dr Wong said. He added the study showed that knowing the HIV status of expectant mothers was definitely beneficial in ensuring the HIV was not passed on.

"We have to know the HIV status of mothers before we can have intervention," he said. "Universal testing is one option we can explore."

The Advisory Council on Aids has recommended that a universal screening programme be implemented to prevent transmission of HIV to babies.

Dr Wong said he could not comment on the Government's position on universal screening, before adding: "But we know there's a good scientific basis supporting that testing is an effective means of reducing perinatal transmission, which can be more effective than behavioural modification."

He also raised concerns about a sharp increase in the number of injecting drug users who became infected, with nine cases reported last year. With the six cases in 1999, these account for half of the HIV infections among injecting drug users since surveillance began in 1984.