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Objectives: To adapt and improve methodology for back-calculation of AIDS in Europe and to examine the feasibility of estimating past HIV incidence by birth cohort., Methods: Empirical Bayesian back-calculation (EBBC) used Markov disease progression models, modified to allow for three diseases added to the AIDS case definition in 1993 and for pre-AIDS mortality, and estimation by penalized maximum likelihood with a neighbour prior. EBBC by 5-year birth cohort assumed a minimum age at infection and age-dependent progression rates; three versions, with varying age effects, were investigated using AIDS cases diagnosed prior to the introduction of highly active antiretroviral therapies (HAART)., Results: Compared with the no age-effect version, EBBC by birth cohort tended to produce flattened HIV incidence curves in country-exposure groups with < 1000 AIDS cases, reflecting effects of the neighbour prior when data become sparse. Otherwise, birth cohort analysis, with moderate effects of age on progression, gave initially increasing incidence curves and consistent patterns across countries, with the 1960-1964 cohort most affected. In the European Union, incidence is estimated to have peaked in 1983 among homosexual men and in 1988 among injecting drug users; 460000 persons were estimated to be living with HIV/AIDS at the end of 1995., Conclusions: Our improved methodology deals effectively with the change in AIDS case definition and has allowed quantitative assessments of the HIV epidemic by birth cohort using all AIDS cases diagnosed before 1996, thus providing a sound basis for public health policy at a time when estimation of more recent prevalence is compromised by the effects of HAART.

Objectives: To study trends in AIDS incidence in Europe by age and year of birth., Design: Age-period-cohort analyses were adopted to distinguish the different time factors of calendar year, age and year of birth., Methods: Non-aggregate AIDS incidence data from 12 European countries (1978-1994) were adjusted for reporting delay and expressed per unit of population (per 100000 persons or 100000 person-years). Age-specific incidence patterns (absolute level and rate of increase) were compared between 5-year birth cohorts for homo-/bisexual men, injecting drug users (IDU) and heterosexual contact cases., Results: Mean age at diagnosis increased strongly amongst IDU, but less so among homo-/bisexual men and heterosexual contact cases. Of a total 110646 reported cases (116311 after adjustment for reporting delay), 87167 (78.8%) were among people born in 1950-1974 [91951 (79.1%) after adjustment for reporting delay]. The relative impact on specific birth cohorts differed strongly by exposure group. Incidences at age ranges of 20-24 and 25-29 years among cohorts born in 1965 and after were about the same level (homo-/bisexual men, IDU) or higher (heterosexual contact cases) than older birth cohorts when these were in the same age range; rates of increase were less among homo-/bisexual men and IDU, but higher among heterosexuals. There were large differences between counties., Conclusions: Overall, AIDS incidence among cohorts born in 1965 and after is about the same level (homo-/bisexual men, IDU) or higher (heterosexual contact cases) than older cohorts when these were in the same age range. Rates of increase of AIDS incidence curves suggest reduced HIV transmission amongst the most recent cohorts of homo-/bisexual men and IDU, but among young heterosexuals the epidemic is still expanding.

Objective: To assess the prevalence of HIV infection and related risk factors among Dutch expatriates returning from assignment in sub-Saharan Africa, Latin America, and South and South-east Asia., Methods: From July 1994 to January 1996, a questionnaire on the risks of sexual exposure was completed by 864 respondents, and blood samples were taken., Results: Of the 634 men, 41% reported having sex with casual or steady local partners and 11% with casual or steady expatriate partners, during an average stay of 26 months in the previous 3 years. Of the 230 women, these figures were 31 and 24%, respectively. Of the men with local casual partners (29%), 59% paid for sex at least once. For men as well as women, having sexual contacts abroad was associated with younger age, positive intention prior to departure to have sex abroad, being single at departure, and, only for the men, working for a commercial organization, and feelings of loneliness and boredom. Among men, consistent condom use with casual local partners was 69%, and with casual expatriate partners 63%. Among women, these figures were 64 and 48%, respectively. Consistent condom use with steady local or expatriate partners was much lower. Among men, non-consistent condom use with casual partners was more prevalent if they had been abroad for a longer time, condoms were not taken along from The Netherlands, the country where they were posted was Asian, and the estimated HIV prevalence among the local population was lower. Among the women, non-consistent condom use was more prevalent if condoms were not taken along, and if they did not have the intention before departure to have sex abroad. Of the persons from whom blood could be obtained, one man was HIV-positive. Another man who refused to participate in the study indicated that he was HIV-positive., Conclusions: Although 23% of the expatriates had unprotected sex with partners from endemic areas, very few HIV infections were found. In comparison with a previous study among this population carried out in 1987-1989, which found five out of 1968 expatriates to be HIV-infected, consistent condom use with casual local partners did increase considerably (from 21 to 67%). However, health education is needed to reduce the risk of HIV infection, which should emphasize the sociocultural differences in sexual practices.