Sexual intercourse (male/female) is relatively low-risk except when the infection is brand new. Most of the spread from person to person seems to occur when the infected person has just been recently infected, few days, few weeks perhaps. Viral loads in that setting are known to be extremely high meaning that there may be more than 2 million virus particles per unit in the blood as opposed to later on in the infection when there may be a few hundred. Therefore, when body fluids are exchanged, they are exchanged with a very rich load of viruses. So that's where infections seem to cluster. Patients are not particularly ill most of the time. A few people feel like they are ill with some fever or sore throat, a little headache and maybe some swollen lymph nodes, but no worse than maybe a little more severe than an average cold. They aren't always in a major way ill. Which means that they are not going be lying in bed waiting for their next dose of aspirin. They're going be out living life, including having sexual contact. I think it's important for people to understand that you can get HIV from sexual intercourse, but not necessarily each and every time. Even without a condom, if a person is in a relatively low viral load in their blood it might be less likely for them to transmit the virus. However, that's playing Russian roulette. I don't know if Russian roulette translates into all cultures, but it's a risky game. If a person gets away with it 19 times maybe the 20th time they'll get infected. It's not worth the risk. How do we minimize the risk? Well, one is to use condoms. Condoms are typically latex rubber coverings of the penis. This can be used during sexual intercourse. Even though it's not perfect, even though sometimes they can break, even though sometimes they can slip, it is actually a very effective tool. There have been scientific studies done where one person, let's say a man, is infected and their sexual partner, let's say a woman, is not infected. They've been counseled but say we are going to have sexual intercourse anyway. When people have been counseled to use condoms and followed up over a year's time, the couples who said they always used condoms each and every time, none of the uninfected people became infected. On the other hand, people who said they rarely used condoms, a large number, perhaps 25 percent of the people became infected. But those who said they mostly used condoms, were almost as likely to have an infection transmission as the ones who almost never used condoms. The only group that escaped was the group that consistently used condoms. So that's evidence that condoms work. For all their faults they definitely can work, but they have to be used each and every time, and they have to be used properly. Education about condoms, the fact of even what they are is not universal. There are people in the world who do not know what a condom is no matter what name you call it. In addition, there are many of those who generally have an idea of what it is but don't know how to use it properly. And finally there are those who may know all of those things but can't get the condom, either because of expense or because of government prohibition or because of societal prohibition. Finally there are those who can know what the condoms are, they know how to use them, they'd like to use them and there's availability, they have them, but they run into resistance from their sexual partner. The resistance can be... complete. In other words, a woman whose livelihood depends on her husband bringing home some money from his job, and she in turn runs the household and keeps the children going, if he says if you make me wear a condom I will leave you, that woman is very unlikely to insist on using a condom, even if her husband has been known to be unfaithful in the past and therefore at risk of having HIV or indeed of having HIV. She'll be unwilling to put herself and her children out on the streets of some very poor neighborhood with no support. And so there's resistance to the use of condoms, governmental resistance and religious resistance occur. Condoms are the only proven tool for preventing HIV transmission. Again, it's a proven tool, not 100 percent foolproof in every instance forever, but if people would consistently around the world always each and every time they have sex use this, there would be several consequences. One, much less HIV transmission, much less transmission of other sexually transmitted diseases, and fewer unintended pregnancies.