Global surveillance and forecasting of AIDS

Abstract

The short-term forecasting of future AIDS cases has been attempted by statistical extrapolations of the observed curve of reported AIDS cases. In areas where such reporting is very incomplete or has only recently started, extrapolation is not possible and an epidemiologically-based forecasting model has been developed to estimate the annual number of AIDS cases which may have occurred and to project the annual number and distribution of AIDS cases for up to ten years. This model, which relies on the current understanding of the epidemiology and natural history of HIV infections and on the available HIV serologic survey data, is used to provide estimates and short-term projections of AIDS cases for the USA, Europe, Africa and the world. Because of the very long (mean of 8-9 years) incubation period between HIV infection and the development of AIDS, new cases over the next five years will be mostly derived from persons who became infected with HIV in or before 1987. WHO has estimated that 5-10 million persons worldwide were infected with HIV in 1987. Based on the lower estimate of 5 million, the cumulative number of AIDS cases which can be projected for the end of 1991 is over one million, and for the mid-to-late 1990s could reach 2 to 3 million. HIV/AIDS will therefore be an increasing public health problem throughout the world. Health care systems everywhere will have to be strengthened to respond to this large toll of disease and death due to AIDS.

PIP: AIDS forecasting is largely influenced by not only the proportion of individuals with HIV infection but also the number of cases that will most likely develop into AIDS. It is expected that the total number of AIDS cases will be over 1 million by the early 1990s. This figure is forecasted to double or triple by the end of the 90s. AIDS reporting to the Global Program on AIDS within WHO has been classified into 3 patterns based on urban/rural location, country and sexual preference. The earliest pattern shows transmission among homosexual and bisexual men and intravenous drug users. The latest pattern demonstrates transmission among both the heterosexual and homosexual population often as a result of travel through areas of patterns I and II. The full range of infection has only been observable for the past 7 years. Among those who are infected, it is estimated that approximately 1/2 of them will develop AIDS. For accurate forecasting, it is necessary to know the starting year of infection in addition to the cumulative presence and the cases of infection reported each year. However accurate the reporting and forecasting, it is safe to predict that the number of AIDS cases will continue to grow steadily as the infection develops. The primary challenge for public health facilities and personnel will be in the education and promotion of prevention against this rising epidemic.