HIV Superinfection: More Questions Than Answers

Studies have reported HIV superinfection incidence rates of between 0 and 7.7 percent per year, but these data, as with much of the understanding about the phenomenon of people with HIV becoming infected with a second strain of the virus, are relatively hazy, and much more research is needed.

http://www.poz.com/articles/superinfection_virus_761_24055.shtml