问：I am go glad to contact you. I am in UK. I donot have a Chinese software, so I have to write this one in English. I am so sorry for that. I would like to ask you some questions about AIDs. Is mouth to mouth kiss dangerous or not if your partner is HIV positive? One of my friend, who is gay, also want to know how dangerous to have an oral sex with a man who is HIV positive since the gay usually donot wear condom for oral sex? How can a gay protect himself from HIV if you donot wear a condom for an oral sex? AIDS seems have a long period development before it become dangerous disease. Is any chance that a person, who is HIV carrier, can be tested HIV negative because this long term period potential. Can he transfer hispotential HIV virus to the people even he is tested negative for HIV? Can I say is it 100% safe if I have a sex with a person, who just test HIV negative? Thank you very much and I would be very appreciate to you if you can help me to answer above quesiton, which are real important to me and my friend.

　　张大夫答：在爱滋病患者的血液、体液和分泌物(包括唾液)中都可以检测到病毒。但爱滋病一般却很少会由接吻传染，因为毕竟唾液中病毒含量微小，完整的口腔粘膜不易侵入，即使病毒进入消化道也容易被胃酸杀死。不过谁都不能保证口腔粘膜、生殖器粘膜没有微小的破损，所以仍然存在少量病毒入侵破损粘膜的危险性。一般感染爱滋病病毒后2-3个月能够检测出来，时间长的6个月以后也能够检测出来，如果在这之前发生性行为，即使病毒检测是阴性，也可以传染。