Malaria incidence in children in South-West Burkina Faso: comparison of active and passive case detection methods.
BACKGROUND
The aim of this study was to determine the incidence and seasonal pattern of malaria in children in South-West Burkina Faso, and to compare, in a randomized trial, characteristics of cases detected by active and passive surveillance. This study also enabled the planning of a malaria vaccine trial.


METHODS
Households with young children, located within 5 kilometers of a health facility, were randomized to one of two malaria surveillance methods. In the first group, children were monitored actively. Each child was visited twice weekly; tympanic temperature was measured, and if the child had a fever or history of fever, a malaria rapid diagnostic test was performed and a blood smear collected. In the second group, children were monitored passively. The child's parent or caregiver was asked to bring the child to the nearest clinic if he was unwell. Follow up lasted 13 months from September 2009.


RESULTS
Incidence of malaria (Fever with parasitaemia ≥5,000/µL) was 1.18 episodes/child/year in the active cohort and 0.89 in the passive cohort (rate ratio 1.32, 95% CI 1.13-1.54). Malaria cases in the passive cohort were more likely to have high grade fever; but parasite densities were similar in the two groups. Incidence was highly seasonal; when a specific case definition was used, about 60% of cases occurred within the 4 months June-September.


CONCLUSIONS
Passive case detection required at least a 30%-40% increase in the sample size for vaccine trials, compared to active detection, to achieve the same power. However we did not find any evidence that parasite densities were higher with passive than with active detection. The incidence of malaria is highly seasonal and meets the WHO criteria for Seasonal Malaria Chemoprevention (SMC). At least half of the malaria cases in these children could potentially be prevented if SMC was effectively deployed.
Centre National de Recherche et de Formation sur le Paludisme (CNRFP), Ouagadougou, Burkina Faso.
Alfred B
AB
Tiono
Centre National de Recherche et de Formation sur le Paludisme (CNRFP), Ouagadougou, Burkina Faso.
David T
DT
Kangoye
MRC Tropical Epidemiology Group, London School of Hygiene & Tropical Medicine (LSHTM), London, United Kingdom.
Andrea M
AM
Rehman
Centre National de Recherche et de Formation sur le Paludisme (CNRFP), Ouagadougou, Burkina Faso.
Désiré G
DG
Kargougou
Centre National de Recherche et de Formation sur le Paludisme (CNRFP), Ouagadougou, Burkina Faso.
Youssouf
Y
Kaboré
Centre National de Recherche et de Formation sur le Paludisme (CNRFP), Ouagadougou, Burkina Faso.
Amidou
A
Diarra
Centre National de Recherche et de Formation sur le Paludisme (CNRFP), Ouagadougou, Burkina Faso.
Esperance
E
Ouedraogo
Centre National de Recherche et de Formation sur le Paludisme (CNRFP), Ouagadougou, Burkina Faso.
Issa
I
Nébié
Centre National de Recherche et de Formation sur le Paludisme (CNRFP), Ouagadougou, Burkina Faso.
Alphonse
A
Ouédraogo
Serum Statens Institute, Copenhagen, Denmark.
Brenda
B
Okech
MRC Tropical Epidemiology Group, London School of Hygiene & Tropical Medicine (LSHTM), London, United Kingdom.
Paul
P
Milligan
Centre National de Recherche et de Formation sur le Paludisme (CNRFP), Ouagadougou, Burkina Faso.
Sodiomon B
SB
Sirima
D002050:Burkina Faso / Q000453:epidemiology; D002675:Child, Preschool; D062665:Epidemiological Monitoring; D004912:Erythrocytes / Q000469:parasitology; D005260:Female; D005334:Fever / Q000175:diagnosis* / Q000453:epidemiology / Q000469:parasitology / Q000503:physiopathology; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D007223:Infant; D007231:Infant, Newborn; D016778:Malaria, Falciparum / Q000175:diagnosis* / Q000453:epidemiology / Q000469:parasitology / Q000503:physiopathology; D008297:Male; D018512:Parasitemia / Q000175:diagnosis* / Q000453:epidemiology / Q000469:parasitology / Q000503:physiopathology; D010963:Plasmodium falciparum / Q000254:growth & development; D012306:Risk; D012621:Seasons