Evaluation of the pyrogenic threshold for Plasmodium falciparum malaria in naive individuals.

A retrospective statistical analysis of two independent data sets was undertaken to determine the peripheral Plasmodium falciparum parasitemia associated with the onset of fever in naive human hosts, and to assess the dynamics of this threshold during the course of the infection and subsequent reinfection. Analysis indicated that there were significant differences between the thresholds for different P. falciparum strains in one data set, and significant interactions between host ethnicity and parasite strain in the other. During untreated infections, the parasitemia associated with the onset of the second fever episode was significantly higher than that causing the first fever (P < 0.02). The parasitemia associated with the first fever episode of a reinfection was elevated relative to the threshold for the first fever episode of the initial infection; however, this difference reached statistical significance only in one of the data sets. These results provide further information on the pyrogenic threshold of malaria.