Projections of the HIV/AIDS epidemic for homosexual/bisexual men in France, the Federal Republic of Germany and the United Kingdom

Back-calculation and projection of the HIV/AIDS epidemic among homosexual/ bisexual men in three European countries: evalution of past projections and updates allowing for treatment effects

This study critically evaluates the quality of 1990 back-calculations and long-term projections of the HIV/AIDS epidemic for homosexual/bisexual men in France, the Federal Republic of Germany, and the UK. The projection captured the general pattern observed in all three countries although the observed AIDS incidence peaked 2-3 years later and declined faster than had been projected. Total AIDS incidences from 1989 to 2000 were overestimated by 38.5% in France, and underestimated by 23.9 and 17.5% in western Germany and the UK. Updated back-calculations and projections to 2020 use AIDS incidence data up to 2000. The procedure incorporates an asymmetric long-tailed cumulative HIV curve as well as the increase in the median incubation period brought about by new therapies introduced during the 1990s. The results suggest that: (i) The rapid decrease in cases during the late 1990s was caused by a median incubation period that increased from 10 years to 21-23 years by the late 1990s. (ii) An imminent bottoming out followed by a protracted increase in AIDS cases from 2000 to at least 2010 could be the consequence of a leveling off of the median incubation period. (iii) A low variant of the projections shows that at least 40,000 homosexual men could develop AIDS in the three countries after 2000.

Human retroviruses

It was only in 1980 that the first human retrovirus, HTLV-1, was isolated. Since then, HTLV-2, HIV-1 and HIV-2 have been identified. All four viruses are transmitted with varying efficiency sexually, vertically from mother to infant, and through blood by transfusion or contamination. HTLV-1 is endemic in populations in south-west Japan, Taiwan, sub-Saharan Africa, the Caribbean, southern USA, central and south America, Australia, Papua New Guinea, Solomon Islands and western Asia. There is now epidemic spread amongst IVDUs in north and south America and southern Europe. HTLV-1 is the aetiological agent of adult T-cell leukaemia/lymphoma (ATL) and tropical spastic paraparesis/HTLV-1 associated myelopathy (TSP/HAM). Other associations which may be causative are with polymyositis, infective dermatitis, gastrointestinal malignant lymphoma and chronic lymphatic leukaemia. ATL appears to be due to malignant transformation of HTLV-1 infected cells, and TSP/HAM to chronic activation of these cells. The epidemiology of HTLV-2 is being separated only recently from HTLV-1 through the application of PCR. It has a low level of endemicity in populations of central Africa, and central and south America. It is being spread epidemically amongst IVDUs in north America and southern Europe. Its association with any pathology in man remains uncertain. HIV-1 is epidemic and spreading rapidly throughout the world. In areas where homosexual contact was the predominant mode of transmission, heterosexual spread is becoming increasingly important. The areas where heterosexual contact is the predominant mode of transmission include the worst affected populations in the world, for example sub-Saharan Africa and some of the Caribbean. There have been recent and explosive increases of HIV-1 seroprevalence in IVDUs and female prostitutes in Asia, especially Thailand and India. Of the diverse pathology following infection, only the haematological consequences are reviewed in detail: these include anaemia, leucopenia, thrombocytopenia, disorders of coagulation and lymphomas. HIV-2, compared to HIV-1, is less infectious and causes less immunosuppression with more slowly progressive disease. It is prevalent in west Africa, but is spreading, albeit slowly, far beyond.