ADJUSTING AIDS INCIDENCE FOR NONSTATIONARY REPORTING DELAYS - A NECESSITY FOR COUNTRY COMPARISONS

In many industrialized countries, infection with the human immunodefic iency virus (HIV) is one of the leading causes of mortality in adult p ersons below age 45. The incidence of the acquired immunodeficiency sy ndrome (AIDS) from surveillance systems is the most common indicator t o compare the situation of the HIV-epidemic in different geographic re gions or countries. Due to reporting delays, AIDS diagnoses in recent years are incompletely reported and need to be estimated. In this stud y, we analyze reporting delays in Switzerland and Spain for the period from 1988 to mid-1995 and estimate the number of AIDS diagnoses per y ear. A descriptive analysis for Switzerland shows increasing reporting delays In recent years. Then, a Bayesian generalized linear model on reverse-time hazards is used to model time trends of the reporting del ay distribution. The model shows that in recent years (i) for Switzerl and reporting delays became longer and yearly AIDS incidence might con tinue to increase, and (ii) for Spain, reporting delays became conside rably shorter resulting in too large estimates of yearly AIDS incidenc e if stationarity of reporting delays is assumed. Critical issues of m odeling non-stationarity of the reporting system are discussed and it is emphasized that estimates of recent RIDS incidence can be biased si gnificantly if time trends of reporting are ignored - as in the exampl e of Switzerland and Spain, this may severely distort comparisons of t he AIDS epidemic in different countries.