Results from a study of the vaginal microbicide candidate Ushercell suggest it was not effective in preventing HIV infection, researchers told this week's 4th International AIDS Society Conference in Sydney. The gel contains cellulose sulphate, a cotton-based compound.

"We don't think it's effective, and there may be an indication of increased risk [of contracting HIV]," said Lut van Damme, international clinical research manager at Conrad, a US-based research group. Interim analysis of data from the trial, which enrolled about 1,400 women, showed 25 who used Ushercell contracted HIV, compared to 16 women using a placebo. Based on that data, Conrad shut down the trial in January.

Ten previous studies and two contraceptive trials had shown the gel was safe.

Van Damme said the surprising interim data might have several explanations. She said Ushercell might have caused irritation or disturbed the natural vaginal flora. A new US safety study of Ushercell is planned involving 60 women, said van Damme. "It would be unethical not to try and understand what's going on," she said.

An Ushercell trial in Nigeria was stopped when Conrad's trial was suspended, even though its data showed no apparent increased risk of HIV among those using the gel, Willard Cates of Family Health International told the conference.

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