Koopman JS, Simon CP, Jacquez JA, Haber M, Longini IM; International Conference on AIDS.
Int Conf AIDS. 1992 Jul 19-24; 8: C261 (abstract no. PoC 4101).
Dept. of Epid., Univ. of Michigan.
OBJECTIVES: The absolute and relative transmission probabilities for receptive oral and receptive anal sex in homosexual males were estimated. Specification of these for primary infection before antibody develops, in the early antibody positive stage, and in late infection was attempted. Average reproduction numbers and anal and oral sex partnership rate thresholds for epidemic and endemic transmission during primary infection were sought. METHODS: At the Chicago Site of the Multicenter AIDS Cohort Studies, a special study on Coping and Change determined the number of four different classes of partners and the number of receptive anal and oral sex acts with these. Data was collected retrospectively in 1984 and prospectively at six month intervals since. To estimate transmission probabilities we fit this data to two types of models: 1) probability of transmission models using observed seroconversions during intervals where behavior was prospectively observed, and 2) deterministic compartmental models using all observed HIV antibody and sexual behavior results. Both models use the contact pattern information intrinsic to specifying different partner types and assume specific contact patterns within these partner types. RESULTS: The study began on the falling slope of an epidemic curve compatible with an SEIR process with a period of transmissibility lasting about two months. Per sex act transmission probabilities are high for anal sex during primary infection before antibodies develop and explain a high proportion of the infections in homosexual males. Right after antibody develops, transmission probabilities are very low and do not account for many infections. Receptive oral sex has less than one sixth the risk of receptive anal sex. Average reproduction numbers observed during the early stages of the epidemic and attributable to primary infection are less than two. CONCLUSIONS: The early stage of the epidemic in homosexual males was driven by transmission before antibody was developed. Transmission fell primarily because of SEIR transmission dynamics rather than behavior change. Behavior change, however, has most likely reduced transmission during primary infection to below threshold levels. Oral sex alone might sustain transmission among that segment of the homosexual population that engages in many oral acts with many partners.
Publication Types:
Keywords:
- Acquired Immunodeficiency Syndrome
- Chicago
- Communicable Diseases
- HIV Infections
- HIV Seropositivity
- Homosexuality
- Homosexuality, Male
- Male
- Probability
- Sexual Behavior
- transmission
Other ID:
UI: 102199523
From Meeting Abstracts