Longitudinal estimation of Plasmodium falciparum prevalence in relation to malaria prevention measures in six sub-Saharan African countries
Authors: Drakeley Chris , Abdulla Salim , Agnandji Selidji Todagbe , Fernandes José Francisco , Kremsner Peter , Lell Bertrand , Mewono Ludovic , Bache Bache Emmanuel , Mihayo Michael Gabriel , Juma Omar , Tanner Marcel , Tahita Marc Christian , Tinto Halidou , Diallo Salou , Lompo Palpouguini , D’Alessandro Umberto , Ogutu Bernhards , Otieno Lucas , Otieno Solomon , Otieno Walter , Oyieko Janet , Asante Kwaku Poku , Dery Dominic Bon-Ereme , Adjei George , Adeniji Elisha , Atibilla Dorcas , Owusu-Agyei Seth , Greenwood Brian , Gesase Samwel , Lusingu John , Mahende Coline , Mongi Robert , Segeja Method , Adjei Samuel , Agbenyega Tsiri , Agyekum Alex , Ansong Daniel , Bawa John Tanko , Boateng Harry Owusu , Dandalo Léonard , Escamilla Veronica , Hoffman Irving , Maenje Peter , Martinson Francis , Carter Terrell , Leboulleux Didier , Kaslow David C. , Usuf Effua , Pirçon Jean-Yves , Bahmanyar Edith Roset 
Published: October 2017

Abstract
Background
Plasmodium falciparum prevalence (PfPR) is a widely used metric for assessing malaria transmission intensity. This study was carried out concurrently with the RTS,S/AS01 candidate malaria vaccine Phase III trial and estimated PfPR over ≤ 4 standardized cross-sectional surveys.

Methods
This epidemiology study (NCT01190202) was conducted in 8 sites from 6 countries (Burkina Faso, Gabon, Ghana, Kenya, Malawi, and Tanzania), between March 2011 and December 2013. Participants were enrolled in a 2:1:1 ratio according to age category: 6 months–4 years, 5–19 years, and ≥ 20 years, respectively, per year and per centre. All sites carried out surveys 1–3 while survey 4 was conducted only in 3 sites. Surveys were usually performed during the peak malaria parasite transmission season, in one home visit, when medical history and malaria risk factors/prevention measures were collected, and a blood sample taken for rapid diagnostic test, microscopy, and haemoglobin measurement. PfPR was estimated by site and age category.

Results
Overall, 6401 (survey 1), 6411 (survey 2), 6400 (survey 3), and 2399 (survey 4) individuals were included in the analyses. In the 6 months–4 years age group, the lowest prevalence (assessed using microscopy) was observed in 2 Tanzanian centres (4.6% for Korogwe and 9.95% for Bagamoyo) and Lambaréné, Gabon (6.0%), while the highest PfPR was recorded for Nanoro, Burkina Faso (52.5%). PfPR significantly decreased over the 3 years in Agogo (Ghana), Kombewa (Kenya), Lilongwe (Malawi), and Bagamoyo (Tanzania), and a trend for increased PfPR was observed over the 4 surveys for Kintampo, Ghana. Over the 4 surveys, for all sites, PfPR was predominantly higher in the 5–19 years group than in the other age categories. Occurrence of fever and anaemia was associated with high P. falciparum parasitaemia. Univariate analyses showed a significant association of anti-malarial treatment in 4 surveys (odds ratios [ORs]: 0.52, 0.52, 0.68, 0.41) and bed net use in 2 surveys (ORs: 0.63, 0.68, 1.03, 1.78) with lower risk of malaria infection.

Conclusion
Local PfPR differed substantially between sites and age groups. In children 6 months–4 years old, a significant decrease in prevalence over the 3 years was observed in 4 out of the 8 study sites.
Trial registration Clinical Trials.gov identifier: NCT01190202:NCT. GSK Study ID numbers: 114001