Expert: John Thai, M.D. - 9/11/2007

Question
Dear Dr.,

I recently read some interesting information about HIV transmission, which I merely need clarification on.

"A sufficient amount of HIV must enter the blood of an uninfected person for infection to be established.  If insufficient HIV enters the bloodstream, transmission of HIV infection will not occur."

I have heard of gay men who bareback bottom for an HIV+ top, ejaculation in the anus occurs, and still, the bottom does not seroconvert.

Please explain how "amount" constitutes infection probability and how someone can have HIV+ ejaculate in his anus and NOT contract HIV.

Thank you.

Answer
Hi Domonic,

That statement most likely refers to transmission from infected needles or droplets of blood due to a scrape/cut. There are individuals who are "lucky" because the virus is unable to infect them even with bb. All negative T/B/V men are at increased risk of contracting HIV while performing any type of unsafe intercourse with a HIV positive individual, whether he/she is straight, bi, or gay.

If a used needle contains HIV virus, there is still a chance of infecting anyone who handles it improperly. It depends on several factors:

1. Immune system. The host, meaning the individual handling the infected product, can either be healthy or unhealthy. If he/she is unhealthy and their immune system is weaken, they are either termed immunocompromised or immunosuppressed.
2. Amount of virus present in the infected product. There is no scientific evidence supporting the quantitative value, as in how much is needed, to infect an individual. However, it is known that the fewer the number of active viruses present, the higher the chances it will infect the host.
3. Type of transmission. This is very important. In bb, aka raw, the individual is at higher risks of contracting any infection. Anal sex can infect both the top or bottom at any given time. The exact method of how the virus chooses its host is still unknown. What we do know is that less than 1% of the population has a different class of receptors on the cells, which allows them to not accept the virus. Another key to an increase risk of contraction is if there are open cuts/wounds in the anorectal region. If there are actively unhealed hemorrhoids, there is a higher risks. If there is an anal/rectal fissure, there is a higher risks. If there is trauma to the area due to unsafe practices like trying to widen the anal opening with various appliances or rough handling of the area or use of toxic lubricants/liquids/fluids, it will increase the risks. The use of toxic chemicals in the anorectal region, such as applying recreational/illegal substances (i.e. cocaine, meth/tina, etc) can irritate and damage the lining of the interior walls of the anus and rectum. This would increase the chances of infection.

As a common sense, it is not safe to perform raw/bb intercourse. You must use your best judgment. Thus, always use a condom.

Regards,

John T, MD