Gay lobby groups are campaigning to overturn a rule that forbids male homosexuals from giving blood in Switzerland. The ban on practicing homosexual males is aimed at preventing the spread of HIV through blood donations. All donated blood is screened for diseases, but if a donor who is HIV positive has not yet developed sufficient antibodies to be detected by tests, he may test negative. So the ban is considered by the Swiss authorities to be a further safeguard. The Swiss Aids Federation says that, in this country, the spread of HIV/AIDS is most prevalent among practicing gays, African migrants and intravenous drug users. (RTS/swissinfo.ch)