By David Willey
BBC News, Rome
The Catholic Church is due to discuss the use of condoms to fight Aids at a conference on infectious diseases opening at the Vatican.
The Pope has backed abstinence over condoms
The Catholic Church formally opposes any use of condoms, advising fidelity within marriage or sexual abstinence.
A senior Vatican cardinal has even publicly questioned the efficacy of condoms as a barrier.
But, as the UN reports growing levels of infection, there are signs a shift of Vatican policy is being discussed.
Pope Benedict XVI has commissioned a report on the scientific and moral aspects of the use of condoms.
Call for change
The head of the Vatican's Council for pastoral health care, Cardinal Lozano Barragan from Mexico, announced that the 200-page report has now been passed on to top theologians for possible use in a papal document.
Several prominent Church officials, including Cardinal Martini, the former Archbishop of Milan, have already called for a change in Catholic teaching.
They say that Church should consider allowing the use of condoms by married couples where one partner is affected by HIV or Aids.
This week's conference of health care workers will consider the problem both from scientific and ethical standpoints.
Cardinal Lozano Barragan says the spread of epidemics and new viral infections constitutes a serious threat to health all over the world.
Until now, the Vatican has been wary of issuing any document which could be interpreted as giving the green light for the use of condoms to stop the spread of aids on the grounds that this would encourage promiscuity.
"No response from the church can encourage a libertine sexual attitude," the Cardinal said.