This document shows estimates of new HIV infections in the United States from 1977 to 2006 broken down by transmission category. The majority of infections were among men who have sex with men, followed by injecting drug use, and a combination of men who have sex with men and injecting drug use. A smaller number of infections were attributed to heterosexual transmission. The estimates are based on an extended back calculation model that specified periods where the number of HIV infections was assumed to remain constant.

1. Estimated new HIV infections by transmission category, extended back calculation model, 50 US states and the District of Columbia, 1977 – 2006 Source : Hall et al. (2008a). 80 000 70 000 60 000 50 000 40 000 30 000 20 000 10 000 0 1977- 1979 1980- 1981 1982- 1983 1984- 1985 1986- 1987 1988- 1990 1991- 1993 1994- 1996 1997- 1999 2000- 2002 2003- 2006 Infections Period Men who have sex with men (MSM) Injecting drug use (IDU) MSM / IDU Heterosexual Figure 23 Tick marks denote the beginning and end of a year. The model specified periods within which the number of HIV infections was assumed to be approximately constant.