Just to have somebody watching makes a huge difference. They get away with it because they can. Supporters say so, but so far no studies have proved it. Even with better data, experts agree that the key to fighting HIV isn't segregation. Many test negative during the window period of early infection and enter the general population with a false sense of security.
Segregated programs reduce rates of seroconversion.
If that is positive, a Western Blot test is done. But it's possible that the inmate will be released before testing is completed, so there's no way of knowing how many prisoners seroconvert while on the inside. A similar study in Illinois found an 0.7 percent rate in 140 prisoners incarcerated for more than 20 years. Just because there's a lot of HIV in prisons doesn't mean people are catching it on the inside. Segregation helps reduce transmission via rape.