colonization with a CD4 count ≤ 200 cells/mm3, viral load, history of shared injections, sex, age, intravenous drug use, underlying disease (hepatitis C, tuberculosis [TB], hepatitis B, Pneumocystis carinii pneumonia [PCP]), having a safe and secure sexual relationship, the use of antiretroviral medication, and the use of prophylactic medication (for PCP and TB). The gene discussed is CD4; the disease is hepatitis C virus infection.