HIV is an infectious disease and the way to spread it can be through blood, through sexual means, and through mother-to-child transmission. The most efficient kind of transmission is directly through the blood, because HIV is higher in the blood, and the greatest possibility of transmission is if HIV goes directly inside the blood. So, the most efficient transmission is through blood. But in practice it is relatively rare, because this is usually sharing needles with people with AIDS, or the blood of people with AIDS coming into contact with other people’s broken wounds. If the contact is only with mucous membranes, the transmission of getting AIDS is likely to go down. So, within these three transmission routes, direct blood transmission is the most efficient, but it is relatively rare.