Risk factors for severe disease in adults with falciparum malaria

Over a 16-year period, we conducted a clinical study of malaria acquired worldwide in adults from malaria-nonendemic countries, to determine risk factors for severe Plasmodium falciparum malaria.

All patients with confirmed malaria who were managed by our unit from 1991 to 2006 were prospectively evaluated. Factors predicting disease severity according to (1) strict World Health Organization (WHO) criteria, (2) a composite measure of unfavorable outcome, and (3) length of hospital stay were identified by logistic and linear regression analyses.

We evaluated 676 episodes of malaria, 482 (71%) due to P. falciparum and 194 (29%) due to nonfalciparum parasites. Black patients had a significantly reduced risk of developing WHO-defined severe falciparum malaria, with Asian patients having odds of severe falciparum malaria that were 8.05-fold (95% confidence interval [CI], 2.93-22.1-fold) higher and white patients having odds that were 8.20-fold (95% CI, 2.94-22.9-fold) higher. Black patients also had a reduced risk of an unfavorable outcome and of a prolonged stay in the hospital, compared with the risks for white or Asian patients. Of 6 patients with falciparum malaria who died, none were black. In univariate analysis, patients with parasitemias of >or= 2% had odds of severe falciparum malaria 12-fold higher than those of patients with parasitemias of <2% (73% vs. 19%). Patients with a history of previous clinical malaria, regardless of ethnicity, had a significantly reduced risk of WHO-defined severe falciparum malaria (odds ratio, 0.35 [95% CI, 0.15-0.80]).

The findings of this study demonstrate that ethnicity and parasitemia are important independent risk factors for severe falciparum malaria in adults from malaria-nonendemic countries and that a history of previous clinical malaria significantly reduces the risk of WHO-defined severe falciparum malaria.