Epidemiological basis for clinical diagnosis of childhood malaria in endemic zone in West Africa

Diurnal variation in body temperature of Gambian children

Measured fever often forms the basis for defining clinical malaria episodes in children from endemic areas. We measured body temperature every 3 h from 08:00 to 20:00 in 69 children aged 1-5 years during the malaria season in a rural area of The Gambia. Body temperature varied on average by more than one degree Celsius during the course of a day. Mean temperatures were lowest in the early morning and highest in the afternoon. There was a strong positive association between air temperature and body temperature. In highly endemic areas, researchers who use measured fever to assess clinical malaria episodes in population-based surveys should standardize the time of day at which temperature is assessed.

Dynamics of malaria parasitaemia associated with febrile illness in children from a rural area of Madang, Papua New Guinea

Active community and self-reporting surveillance techniques have been used to describe the dynamics of febrile illness and associated malaria infection in children aged 2 to 15 years from a rural area of Madang Province, Papua New Guinea (PNG). Both history of fever and fever in association with parasitaemia appeared to be reliable indicators of malaria morbidity in this endemic area. Parasite density was observed to be a major determinant of mild malarial disease at both the population level and within an individual. Age-specific prevalence of febrile illness correlated with age-specific patterns of parasite density but not of parasite prevalence. Seasonal changes in fever incidence correlated with parasite density. The transition from afebrile to febrile state within an individual was generally associated with an increase in parasite density. Surveillance and self-reported febrile cases (which differ in severity on the basis of the perceived need for treatment) could be distinguished on the basis of parasite density. Thus surveillance techniques divide clinical malaria in rural PNG into 'mild' and 'very mild' forms. The age-specific pattern of decline of prevalence of malaria-associated febrile illness and parasite density is best explained by induction of strain-specific anti-disease immunity upon infection with a given strain of Plasmodium falciparum. The fever threshold in self-reporting febrile cases was seen to decrease with age and can be explained by an age-specific decline in anti-toxic immunity.

What is clinical malaria? Finding case definitions for field research in highly endemic areas

In non-endemic areas, the diagnosis of clinical malaria may be made on the basis of fever and a positive blood film. However, in areas of high endemicity, asymptomatic parasitaemia is very common: to assume that a child who presents with fever and parasitaemia is ill from malaria will result in overdiagnosis. In this article, Jo Schellenberg, Tom Smith, Pedro Alonso and Richard Hayes discuss the relationship between fever and parasite density in such areas, and show how the proportion of fevers due to malaria (the attributable fraction) can be estimated and used to evaluate case definitions for use in field trials.

Classification of clinical falciparum malaria and its use for the evaluation of chemosuppression in children under six years of age in Liberia, west Africa

The possible role of malaria as cause of morbidity was assessed during one year in 262 children aged 6 months to 6 years living in two villages in a rural area of Liberia. The study population was followed by weekly clinics and three-monthly surveys and the children were randomly allocated to receive either chloroquine or placebo every 3 weeks. The morbidity of the children was evaluated by criteria based on the history and the clinical condition into four different stages, in order to describe the probability that an observed clinical event could be attributed to malaria infection, based on the presence of detectable parasites in the blood, the history the previous week, and the clinical status of the child. The level of anaemia, splenomegaly and measured body temperature supported that malaria was the major contributor to the overall morbidity observed. Based on the stage classification of clinical illness, children were classified as having 'possible clinical malaria' or 'probable clinical malaria'. Malaria appeared to be an important cause of febrile episodes during both dry and rainy seasons. During the rainy season more than 60% of the children experienced at least one clinical malaria episode, and during the dry season more than 50% of the children experienced at least one clinical attack of malaria. Children receiving chemosuppression had overall fewer clinical malaria attacks, and the effect of the chemosuppression was most pronounced in the dry season, the odds ratio comparing children receiving regular chemosuppression with children receiving presumptive treatment only was estimated to 0.39 (0.25-0.62).

Usefulness of clinical case-definitions in guiding therapy for African children with malaria or pneumonia

The World Health Organisation has developed disease-specific clinical case-definitions to guide management of children with fever or cough, the cardinal signs of malaria and pneumonia. To assess the usefulness of the case-definitions and to investigate their interaction, we studied children with fever or cough brought to a hospital in Lilongwe, Malawi. For all children, a thick blood smear was examined for Plasmodium falciparum parasites. Chest radiography was done only for children with parasitaemia and those who satisfied the clinical case-definition for pneumonia; others were assumed to have normal chest radiographs. Of 1599 enrolled children, 566 (35%) had parasitaemia and 116 had radiographic evidence of pneumonia; 43 had both pneumonia and parasitaemia. Of the 471 children who met the clinical definition for pneumonia, 449 (95%) also met the malaria clinical definition. Among children with radiographic evidence of pneumonia, the clinical definition for malaria was not predictive of parasitaemia (sensitivity 93%, specificity 5%). Whether malaria parasitaemia was present or absent, the pneumonia clinical definition distinguished children with and without radiographic evidence of pneumonia (sensitivity and specificity > 60%). Children who satisfied the pneumonia clinical definition were more likely to have radiographic evidence of pneumonia (odds ratio 10.4, 95% confidence interval 5.2-20.7), parasitaemia (1.6, 1.2-2.2), or both at the same time (4.2, 2.1-8.4) than were children who did not meet the definition. Children who satisfy the malaria and pneumonia clinical definitions need treatment for both disorders. Scarce diagnostic methods, especially microscopy, are needed for more specific treatment of children with fever and cough.