title: Consistent prevalence of asymptomatic infections in malaria endemic populations in Colombia over time.
abstract: BACKGROUND
  Malaria control programmes rely on confirmation of parasite presence in patients' blood prior to treatment administration. Plasmodium parasites are detected mostly by microscopy or rapid diagnostic test (RDT). Although these methods contribute significantly to malaria control/elimination, they are not suitable for detecting the significant proportion of asymptomatic subjects harbouring low levels of parasitaemia, which endure untreated as potential reservoirs for transmission. Malaria prevalence was assessed in endemic regions of Colombia over a 4-year follow-up.
  
  
  METHODS
  A series of cross-sectional surveys were conducted between 2011 and 2014 in low to moderate malaria transmission sentinel sites (SS) of Tumaco, Buenaventura and Tierralta municipalities of Colombia. A census was performed and a random sample of houses was selected from each SS prior to each survey. Inhabitants were asked to answer a questionnaire on clinical, epidemiological and demographic aspects, and to provide a blood sample for malaria diagnosis using microscopy and quantitative real time polymerase chain reaction (qPCR).
  
  
  RESULTS
  A total of 3059 blood samples were obtained from all SS, 58.5 % of which were from women and displayed a malaria prevalence ranging from 4 % (95 % CI 3-5 %) to 10 % (95 % CI 8-12 %) in the 4 years' study period. Almost all malaria cases (n = 220, 97 %) were sub-microscopic and only detectable by qPCR; 90 % of the cases were asymptomatic at the time of blood collection. While Buenaventura and Tierralta had a decreasing tendency during the follow-up, Tumaco had a rise in 2013 and then a decrease in 2014. Plasmodium vivax accounted for the majority (66-100 %) of cases in Tierralta and Buenaventura and for 25-50 % of the cases in Tumaco.
  
  
  CONCLUSIONS
  This study demonstrates an important prevalence of asymptomatic malaria cases not detectable by microscopy, which therefore remain untreated representing a parasite pool for malaria transmission. This demands the introduction of alternative strategies for diagnosis and treatment, especially for areas of low transmission to reduce it to appropriate levels for malaria pre-elimination efforts to start.
authors: Clinical Trials Unit, Malaria Vaccine and Drug Development Center, Cali, Colombia. juan.vasquez@inmuno.org.
authors: Juan M
authors: JM
authors: Vásquez-Jiménez
authors: Caucaseco Scientific Research Center, Cali, Colombia. marevalo@inmuno.org.|School of Health, Universidad del Valle, Cali, Colombia. marevalo@inmuno.org.
authors: Myriam
authors: M
authors: Arévalo-Herrera
authors: Clinical Trials Unit, Malaria Vaccine and Drug Development Center, Cali, Colombia. Juliana.henao@inmuno.org.
authors: Juliana
authors: J
authors: Henao-Giraldo
authors: Clinical Trials Unit, Malaria Vaccine and Drug Development Center, Cali, Colombia. karen.molina@inmuno.org.
authors: Karen
authors: K
authors: Molina-Gómez
authors: Data Management Unit, Caucaseco Scientific Research Center, Cali, Colombia. maria.arce@inmuno.org.
authors: María
authors: M
authors: Arce-Plata
authors: Molecular Biology Unit, Caucaseco Scientific Research Center, Cali, Colombia. avallejo@inmuno.org.
authors: Andrés F
authors: AF
authors: Vallejo
authors: Clinical Trials Unit, Malaria Vaccine and Drug Development Center, Cali, Colombia. sherrera@inmuno.org.|Caucaseco Scientific Research Center, Cali, Colombia. sherrera@inmuno.org.
authors: Sócrates
authors: S
authors: Herrera
mesh_terms: D058345:Asymptomatic Infections / Q000453:epidemiology*; D003105:Colombia / Q000453:epidemiology; D003430:Cross-Sectional Studies; D006801:Humans; D008288:Malaria / Q000453:epidemiology* / Q000635:transmission; D015995:Prevalence