The risk environment for HIV transmission: Results from the Atlanta and Flagstaff network studies

The Purpose of this study was to investigate the hypothesis that human immu nodeficiency virus (HIV) transmission may be facilitated or obstructed by n etwork structure, incorporating a measure of risk that combines true risk a nd surrogates. Persons at presumed high risk for HIV were enrolled in long- term follow-up studies of urban and rural networks in Atlanta, Georgia, and Flagstaff, Arizona. We focused on respondents who were also contacts to ev aluate information on both sides of the observed dyads and constructed a Ri sk Indicator, based on a four-digit binary number, that permitted assessmen t and visualization of the overall risk environment. We constructed graphs that provided visualization of the level of risk, the types of relationship s, and the actual network. Although some of the findings conform to the hyp otheses relating network structure to transmission, there were several anom alies. In Atlanta, HIV prevalence was most strongly related to men with a m ale sexual orientation, despite the widespread use of injectable drugs. In Flagstaff, an area of very low prevalence and no transmission, the risk env ironment appeared more intense, and the frequency of microstructures was as great or greater than representative areas in Atlanta. The network hypothe sis is not yet sufficiently developed to account for empirical observations that demonstrate the presence of intense, interactive networks in the abse nce of transmission of HIV.