The Los Angeles County Department of Public Health issued an advisory Wednesday urging that men who have sex with men, particularly those with HIV, be vaccinated against invasive meningococcal disease (IMD). IMD is a rare bacterial infection of the blood, spinal cord, and/or brain lining that can be fatal. The department has identified 24 cases in the past 17 months, 7 of those among gay and bisexual men. Eight cases reported this year alone included four gay and bisexual men, three of whom had HIV infection. Three of the four have died. The county and the Los Angeles Gay & Lesbian Center are offering free vaccination.