4% of HIV-positive Americans passed on HIV each year in 1990s, says study

In any given year in the 1990s, at least 95% of HIV-positive Americans did not pass on HIV, according to a US public health investigator writing in the January 1^st edition of the Journal of Acquired Immune Deficiency Syndromes. The study investigator calculates that between 4 - 4.34% of HIV-positive individuals infected somebody else with HIV in any given year in the 1990s.

Dr David Holtgrave from the AIDS Research Center at Emory University calculated the annual HIV transmission rate in the US between 1978 and 2000. Determining annual HIV transmission rates could, Dr Holtgrave suggests, have the potential to provide insights into HIV prevention programmes and indicate areas requiring emphasis.

Statistics on annual AIDS deaths were obtained from the US Center for Disease Control. Annual HIV incidence (the number of new HIV infections a year) between 1978 and 2000 was calculated using a backcalculation method. This is a mathematical technique that infers past distribution of HIV cases using current observations on AIDS cases given the natural history of HIV disease (the reliability of this model, has however, been reduced since the introduction of HAART). The number of people living with HIV in any given year was calculated by subtracting the cumulative number of AIDS deaths from the cumulative HIV incidence rate.

The annual HIV transmission rate was then calculated by Dr Holtgrave by dividing the adjusted HIV incidence for a given year by the estimated number of people living with HIV for that year.

Dr Holtgrave calculated that the annual transmission rate peaked in 1979 at 100% - effectively meaning that every person infected with HIV at this time infected somebody else. However, the annual transmission rate dropped sharply through the 1980s, falling to a little under 5.5% by the end of the decade. Throughout the 1990s the annual transmission rate fell even further, to a stable 4.00 – 4.34%.

The drop in transmission rates is described as “dramatic” by Dr Holtgrave and he suggests that this could be due to “the effectiveness of a variety of HIV prevention programs…clinical effects of HIV treatments available in the late 1990s, the natural history of HIV disease, and overall societal responses to the HIV epidemic.”

Although 95% of HIV-positive individuals did not transmit HIV to somebody else in the 1990s, Dr Holtgrave notes that “during any given year in the 1990s, for 4.34% (or less) of persons living with HIV, an instance occurred in which they and their sexual or drug injecting partner engaged in unsafe behavior resulted in HIV transmission.”

To reduce the annual HIV transmission rate further, Dr Holtgrave recommends that research focus on the “behavioral, clinical, and societal conditions that accompany HIV transmission for these approximately 4.34%…of persons living with HIV.” He further suggests that research should look at the sexual or drug use partners of HIV-positive individuals.

Further information on this website

Survival sex and misconceptions about HAART associated with continued unsafe sex - news story

Americans publish guidelines on how to incorporate HIV prevention into HIV medical care - news story