This may sound like a stupid question, because the answer seems obvious. Since both parties have the virus, there’s no danger in passing it along to anyone. Assuming neither one had any other communicable diseases, it shouldn’t be a problem, right?
Nope, it’s a big problem.
When two HIV positive people have sex it gives the virus a chance to mutate and become resistant to treatment.
There are many different strains of HIV. As bad as it is to be infected with one, it’s even worse to be infected with more than one. I have heard (though I have no cite) that being infected with multiple strains allows the strains to swap DNA, greatly increasing the likelyhood of them developing resistance to antivirals.
Some articles about HIV superinfection.
In the case of a heterosexual coupling, the HIV+ woman can still conceive a baby, with attendant risks of transmission.
This was probably obvious to the OP, but I thought I should point it out anyway.
Odd that this came up now… I read something recently that stated that some scientists question that AIDS “superinfections” actually happen. Damn, I wish I remembered where I read that…
Contrary to what others have posted in this thread, at the latest international AIDS conference, held in Bankok earlier this month, a paper was presented that casts doubt on some long-held ideas of “superinfection” (dual infection with a different type of HIV). Evidence is lacking of superinfection happening at any point other than early infection. The study found no example of superinfection happening to someone in the chronic phase of HIV infection.
Besides HIV superinfection, HIV sufferers are vulnerable to contracting many diseases/infections not contractable by uninfected persons, so it seems there would be an enhanced risk of passing those diseases/infections to another HIV sufferer.
eJournal of the International AIDS Society:
No superinfection among seroconcordant couples after well-defined exposure
MedGenMed. 2004 Jul 11;6(3):ThPeA6949 [eJIAS. 2004 Jul 11;1(1):ThPeA6949]