Lessons from previous predictions of HIV/AIDS in the United States and Japan: epidemiologic models and policy formulation

Abstract

This paper critically discusses two previous studies concerned with predictions of HIV/AIDS in the United States and Japan during the early 1990s. Although the study in the US applied a historical theory, assuming normal distribution for the epidemic curve, the underlying infection process was not taken into account. In the Japan case, the true HIV incidence was estimated using the coverage ratio of previously diagnosed/undiagnosed HIV infections among AIDS cases, the assumptions of which were not supported by a firm theoretical understanding. At least partly because of failure to account for underlying mechanisms of the disease and its transmission, both studies failed to yield appropriate predictions of the future AIDS incidence. Further, in the Japan case, the importance of consistent surveillance data was not sufficiently emphasized or openly discussed and, because of this, revision of the AIDS reporting system has made it difficult to determine the total number of AIDS cases and apply a backcalculation method. Other widely accepted approaches can also fail to provide perfect predictions. Nevertheless, wrong policy direction could arise if we ignore important assumptions, methods and input data required to answer specific questions. The present paper highlights the need for appropriate assessment of specific modeling purposes and explicit listing of essential information as well as possible solutions to aid relevant policy formulation.

Figure 1

Observed and predicted AIDS incidence in the United States from 1981–2003. Data source: refs. [26,27]. Details of the underlying assumptions employed are described in the Additional file. The prediction was obtained using the data up to the dashed line; i.e., from 1981–7. The constant second ratio of AIDS incidence was 0.8647, as adopted in ref. [22].

Figure 2

Observed and predicted numbers of HIV infections and AIDS diagnoses in Japan from 1985–2004. Data source: ref. [44]. The top three panels show the estimated true HIV incidence (a-c) and the bottom show AIDS incidence (d-f). The routes of transmission are heterosexual men (a and d), men who have sex with men (MSM; b and e), and heterosexual women (c and f). The prediction was obtained using the data up to the dashed line; i.e., from 1985–92. The straight lines in a-c represent the predicted true HIV incidence based on the assumption of linear growth. The coverage ratio was 1/5.1 [30,32]. The shape and scale parameters for the Weibull distribution used to describe the incubation period were 2.286 and 10.0, respectively, as adopted in ref. [28].