Actually, it's the right one. What you want to reduce is the incidence of infected people in the donor pool.
http://www.cdc.gov/hiv/topics/surveillance/incidence.htm
CDC estimates MSM represent approximately 2% of the US
population, but accounted for more than 50% of all new
HIV infections annually from 2006 to 2009.
If you can drop your incidence of HIV by 50% while reducing the pool size by only 2%, you've improved the infection incidence in the pool substantially!
You mean we should be talking about rate of infection in a population, rather than their contribution to the raw infection numbers overall?
Yeah. I thought it was implied that we were talking about that, though. I mean, even the casual reader should be able to infer that gay men do not make up anything like half the general population. That would mean there were no straight men at all.
If we have several small populations of people with a high incidence, though, I think the raw contribution is actually the right number to talk about. Consider the following thought experiment:
I have 100 people, and 6 HIV infections. 10 of the people are gay men, and 3 of them are infected. 2 of the people are female prostitutes and both of them are infected.
The general population has a 6% infection rate. The gay men have a 50% infection rate and account for 50% of the infections. The prostitutes have a 100% infection rate and account for 33% of the infections.
The exclusion of which group improves the resulting donor pool more?
If we exclude the men, we are left with 3 infections / 90 people = 3.3%. If we exclude the prostitutes, we are left with 4 infections / 98 people = 4.1%.
Even though the prostitutes have a much higher rate of infection than the gay men, excluding the men helps the final result more because they account for more of the overall infections.
> You mean we should be talking about rate of infection in a population, rather than their contribution to the raw infection numbers overall?
Either is fine. "50% of HIV positive people are gay" is not. For all we know, there are only two HIV positive people, and one is gay and one straight. That's hardly a reason for excluding all gay people from donating...
