AIDS: Although people with HIV are living longer than ever before, they continue to suffer from infections that are associated with low T4-cell counts. The U.S. Public Health Service (PHS) and the Infectious Diseases Society of America (IDSA) have updated the guidelines for preventing opportunistic infections, including their positions on when prophylaxis is indicated. Summaries are given for preventing the following infections: cytomegalovirus (CMV), cryptosporidiosis, fungal infections, human papillomavirus (HPV), herpes-related infections, mycobacterium avium complex (MAC), pneumocystis carinii pneumonia (PCP), streptococcal pneumonia, toxoplasmosis, and tuberculosis.