Changing malaria epidemiology and diagnostic criteria for Plasmodium falciparum clinical malaria

PLoS One. 2012;7(9):e46188. doi: 10.1371/journal.pone.0046188. Epub 2012 Sep 28.

Abstract

Background: In tropical Africa, where malaria is highly endemic, low grade infections are asymptomatic and the diagnosis of clinical malaria is usually based on parasite density. Here we investigate how changes in malaria control and endemicity modify diagnostic criteria of Plasmodium falciparum attacks.

Methods and findings: Parasitological and clinical data from the population of Dielmo, Senegal, monitored during 20 years, are analyzed in a random-effect logistic regression model to investigate the relationship between the level of parasitemia and risk of fever. Between 1990 and 2010, P. falciparum prevalence in asymptomatic persons declined from 85% to 1% in children 0-3 years and from 34% to 2% in adults ≥50 years. Thresholds levels of parasitemia for attributing fever episodes to malaria decreased by steps in relation to control policies. Using baseline threshold during following periods underestimated P. falciparum attacks by 9.8-20.2% in children and 18.9-40.2% in adults. Considering all fever episodes associated with malaria parasites as clinical attacks overestimated P. falciparum attacks by 42.2-68.5% in children and 45.9-211.7% in adults.

Conclusions: Malaria control modifies in all age-groups the threshold levels of parasitemia to be used for the assessment of malaria morbidity and to guide therapeutic decisions. Even under declining levels of malaria endemicity, the parasite density method must remain the reference method for distinguishing malaria from other causes of fever and assessing trends in the burden of malaria.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Antimalarials / therapeutic use
  • Asymptomatic Diseases
  • Child
  • Child, Preschool
  • Diagnosis, Differential
  • Fever / diagnosis*
  • Fever / epidemiology
  • Humans
  • Infant
  • Infant, Newborn
  • Logistic Models
  • Longitudinal Studies
  • Malaria, Falciparum / diagnosis*
  • Malaria, Falciparum / drug therapy
  • Malaria, Falciparum / epidemiology
  • Malaria, Falciparum / parasitology
  • Male
  • Middle Aged
  • Parasitemia / diagnosis*
  • Parasitemia / drug therapy
  • Parasitemia / epidemiology
  • Parasitemia / parasitology
  • Plasmodium falciparum / drug effects
  • Plasmodium falciparum / growth & development*
  • Prevalence
  • Risk Factors
  • Senegal / epidemiology

Substances

  • Antimalarials

Grant support

The Dielmo project was funded by the Institut Pasteur of Paris, the Institut Pasteur of Dakar, the Institut de Recherche pour le Développement (IRD, formerly ORSTOM) and received grants from the Ministry of Cooperation and the Ministry of Research (France). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.