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To determine risk factors and rates of human immunodeficiency virus (HIV) transmission in serologically discordant couples receiving regular safe sex counselling.
This multicentre cross-sectional study of heterosexual human immunodeficiency virus (HIV) involved the collection of serum samples and epidemiological information with emphasis on sexual behaviour. A prospective follow up of sexual partners was done every 6 months for 3 years. Information was collected from the potentially infectious subject (index case) and his or her sexual partner(s).

Questionnaires for 563 couples were received from 13 centres provided the following conclusions:
cross-sectional analysis showed 82 seropositive females among 404 female partners of male index cases, and 19 seropositive male partners among 159 male partners of female index cases;
4 significant factors for male to female (M-F) transmission were evidenced: practice of anal sex; recent sexually transmitted disease for one or both of the partners; full blown acquired immune deficiency syndrome (AIDS) for themale index (compared with less symptomatic male index cases) and age of the partners. The rate of male to female transmission was found to be highly related to these factors. 2 risk factors for female to male (F-M) transmission were also evidenced: sexual contacts during menses of the female index case and full blown AIDS for the female index.
Among 108 nonusers of condoms, 10 seroconversions occurred, whereas no seroconversion had been observed among 107 systematic condom users. Risk factors found through the prospective follow up confirm the major risk factors found in the cross-sectional analysis.

Developments of transmission models using these data are underway and preliminary results suggest that the mean probability of transmission per sexual act is 0.002 for M-F transmission and 0.001 for F-M transmission.

The study was instituted to determine risk factors and rates of human immunodeficiency virus (HIV) transmission in serologically discordant couples receiving regular safe sex counselling. 563 couples were recruited from 9 countries in a cross sectional study. 378 HIV partners recruited in settings where follow up was achievable were included in the prospective study. Only partners presenting no risk factors for HIV infection other than sexual contacts with the index (HIV+ partner) were included. Couples were followed up to June 1992. The follow up rate was 80.4%. 128 couples stopped sexual contacts, mostly because of death or severe disease. 245 couples still having sexual contacts 3 months after inclusion were followed for a median of 22 months. 123 couples used condoms for each episode of vaginal or anal intercourse. No seroconversions occurred among these 123 partners. 12 seroconversions occurred among the remaining 122 partners, or 1.2 per 1000 unprotected contacts. Among irregular condom seroconversion rates (SR) were similar whatever the frequency of condom use or sex of the partner. For partners of symptomatic index cases, SR was 36.7% compared to 8.5% for partners of asymptomatic index cases. SR were different between partners reporting: (1) no sexually transmitted disease (STD) (9.5%), (2) nonulcerative STD (25.0%), and (3) ulcerative STD (40.0%). The SR for female partners were different according to the frequency of sperm ejaculation by male index cases.

The major conclusions were:
no seroconversion occurred in regular condom users;
the observed transmission rate of 1.2 per 1000 unprotected contacts should be interpreted with caution since it may greatly vary according to the presence or absence of risk factors (advanced stage of infection for the index and partner's STD were found to increase the risk, whilst avoidance of sperm ejaculation showed some protective effect).
Sexual transmission is the main mode of transmission of HIV throughout the world. Heterosexual transmission of HIV has been widely documented in Africa and the Caribbean Islands where this route of transmission predominates. Frequency of cases having acquired HIV by heterosexual contact is increasing in Europe and infected partners of persons at risk are now seen more frequently in hospital and clinic consultations.

A multicentre study of the heterosexual transmission of HIV was set up in 1987 to determine the rates of transmission to sexual partners, the sexual behaviours at risk and effectiveness of preventive measures.

Inclusion of couples ended in March 1991, leading to a total of 563 couples included. Since results based on prospective data are more reliable than results based on data recorded retrospectively, a prospective follow-up of serologically discordant couples was planned. Furthermore, the follow-up of couples regularly counselled about risks of HIV transmission unables us to evaluate the efficacy of counselling and condom use. With a minimum follow-up of 12 months for couples last included (March 1991), the prospective phase continued until June 1992.

Between March 1991 and December 1992, the work plan of the concerted action included:
- Analysis (and publication) of data at inclusion for the 563 couples.
- Active follow-up of discordant couples, with a specific investigation during the 1st semester of 1992 to obtain data from couples 'lost to follow-up'.
- Analysis of prospective data.
- Coordination of the European working group for the development and implementation of new research projects regarding AIDS among heterosexuals.


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