Studies of prison populations in California, Virginia, Connecticut, Maryland, and Texas have found HCV infection in 29 to 42 percent of inmates. National figures for HCV infection among incarcerated populations estimate that 15 to 30 percent of inmates across the country may be HCV positive. Injection drug use is the primary transmission route for HCV. High-risk sexual behaviors and injection drug use are the major transmission routes for HBV. A substantial majority of prison and jail inmates have serious drug problems, including injection drug use. Many inmates already have chronic HBV or HCV infection when they enter prison or jail. Because symptoms are often mild or nonexistent, inmates may not know they are infected and can unwittingly transmit the virus to others. There is also a high risk of transmission to the larger community outside of the facility. No specific Federal guidelines currently exist for screening or treating inmates at risk or already infected with HBV and HCV. Such guidelines are currently being developed and should provide facilities with assistance in developing and implementing policies for routine screening, immunization, and medical evaluation and management. Viral hepatitis prevention measures can be expensive. Carrying out these measures can be difficult due to the variable length of sentences and constant movement of inmates within and between facilities. Antiviral therapy for chronic hepatitis B and chronic hepatitis C is complicated, has limited effectiveness, and is not appropriate for everybody. Many inmates have other illnesses and conditions, and treatment of HBV or HCV may not be the highest priority for the correctional health staff. Many correctional facilities already have education, prevention, and treatment programs focused on HIV, sexually transmitted diseases, and substance abuse. Vaccines are available for hepatitis A and hepatitis B.