The probability of transmission from a male to a female is approximately 0.1%-0.2% for a single sexual encounter without the use of a condom. The probability of transmission from female to male is less than 0.1%, and the probability of transmission from male to male is 0.5%-3.0%. From the above data, it can be seen that the chances of transmission between gay men will be higher. Although the chances of infection from these sexual behaviors are low, it may be possible to be infected just once if prevention is not taken. If one partner is acutely infected with HIV or if the patient also has a sexually transmitted disease or a broken genital mucosa, the probability of infection is greatly increased. Unlike other diseases, HIV infection is permanent once contracted. There are no effective drugs to treat it and no effective vaccine to prevent it.