Increasing mortality from thrombotic thrombocytopenic purpura in the United States—analysis of national mortality data, 1968–1991

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Abstract
Thrombotic thrombocytopenic purpura (TTP) is a rare disease and the epidemiologic features have been incompletely characterized. Because of the historically high case-fatality rate for TTP, we analyzed U.S. multiple cause-of-death mortality data with TTP listed on the death record for the period 1968–1991, in order to estimate the incidence of TTP, to characterize demographic features of the decedents, and to determine if trends in mortality correlate with findings from clinical studies showing improved survival in recent years. There were 4,523 TTP-associated deaths during the 24-year study period. The annual age-adjusted mortality rate decreased initially and reached its lowest point at 0.4 per 1,000,000 residents for the years 1970 through 1973, and then increased steadily to 1.1 during the last 4 years of the study period, 1988 through 1991. We estimate the current incidence of TTP to be approximately 3.7 cases per 1,000,000 residents. Deaths were rare below the age of 20 years, but the age-specific mortality rate for those 20 years and older increased steadily with increasing age. Regardless of age, females were affected more often than males, and the overall female-to-male age-adjusted rate ratio was 1.9 (95% confidence interval (Cl), 1.8 to 2.0). The greatest age-specific difference was between females and males in their twenties (rate ratio 3.2; 95% Cl, 2.6 to 3.9). The mortality rate for blacks, and especially black females, was higher than the mortality rate for whites (black-to-white age-adjusted rate ratio 3.4; 95% Cl, 3.2 to 3.6; black female-to-white female age-adjusted rate ratio 3.6; 95% Cl, 3.3 to 3.9), although the majority of deaths were among whites (71.5%). Infection with the human immunodeficiency virus (HIV) or an HIV-related diagnosis was reported in 61 (1.3%) decedents overall and in 51 (4.4%) decedents from 1988 through 1991. The TTP mortality rate has increased over time despite reports of significant improvement in survival associated with clinical use of plasma infusion and plasma exchange. This trend in mortality suggests that the incidence of TTP is increasing. Blacks, and black females in particular, are affected at a disproportionately high rate. The increased incidence of HIV infection and related disease may have contributed to some of the increase in TTP mortality in recent years, but it does not explain the majority of the increase, which began before the onset of the HIV epidemic.