Rates of syphilis and a rare strain of chlamydia called lymphogranuloma vereum (LGV) are up among men who have sex with men (MSMs), increasing their chances of HIV infection. People with syphilis are 3 to 5 times more likely to contract HIV when exposed to the virus, and 64% of new syphilis cases in 2004 were among MSMs, up from just 5% in 1999. LGV’s rectal inflammation and ulceration also increases the HIV risk, and there are at least 80 cases in the U.S., all among MSMs, though many believe the real number is much higher.