title: High prevalence of sub-microscopic infections in Colombia.
abstract: BACKGROUND
  Malaria transmission in Latin America is typically characterized as hypo-endemic and unstable with ~170 million inhabitants at risk of malaria infection. Although Colombia has witnessed an important decrease in malaria transmission, the disease remains a public health problem with an estimated ~10 million people currently living in areas with malaria risk and ~61,000 cases reported in 2012. This study aimed to establish the malaria prevalence in three endemic regions of Colombia to aid in designing new interventions for malaria elimination.
  
  
  METHODS
  A cross-sectional survey was conducted in three regions of Colombia with different malaria epidemiological profiles: Tierralta (Ta), Tumaco (Tu) and Buenaventura (Bv). The Annual Parasite Index (API) was 10.7, 6.9 and 3.1, respectively. Participants were asked to respond to a sociodemographic questionnaire and then were bled to determine the Duffy genotype and the prevalence of malaria infection by microscopy and quantitative real-time PCR (qPCR).
  
  
  RESULTS
  The study was conducted between October 2011 and January 2012. Eight sentinel sites with 1,169 subjects from 267 households were included. The overall prevalence of sub-microscopic infections measured by thick blood smear (TBS) was 0.3% (n=4) whereas by qPCR it was 9.7% (n=113), with a greater proportion (13%) in 40-50 years old individuals. Furthermore, different regions displayed different prevalence of sub-microscopic infections: Bv 12%, Ta 15%, and Tu 4%. From these 113 samples (qPCR), 74% were positive for P. vivax and 22% for P. falciparum, and 4% were mixed infections, which correlates to the overall parasite prevalence in Colombia. This study showed that in the southern Pacific coast of Colombia (Bv and Tu), around 56% of the population have a Duffy-negative genotype, compared to the northern region (Ta) where the percentage of Duffy-negative genotype is around 3%.
  
  
  CONCLUSIONS
  Sub-microscopic infections are prevalent across different regions in Colombia, particularly in areas with relatively low transmission intensity. The poor microscopy results suggest the need for more sensitive diagnostic tools for detection of sub-microscopic infections. This study underscores the importance of conducting active case surveillance to more accurately determine malaria incidence, and highlights the need for updating the malaria guidelines to track and treat sub-microscopic malaria infections.
authors.affiliation: Malaria Vaccine and Drug Development Centre, Cali, Colombia. avallejo@inmuno.org.
authors.forename: Andres F
authors.initials: AF
authors.lastname: Vallejo
authors.affiliation: National Institute of Health of Colombia, Bogotá, Colombia. pchaparro@ins.gov.co.
authors.forename: Pablo E
authors.initials: PE
authors.lastname: Chaparro
authors.affiliation: Caucaseco Scientific Research Center, Cali, Colombia. ybenavides@inmuno.org.
authors.forename: Yoldy
authors.initials: Y
authors.lastname: Benavides
authors.affiliation: Caucaseco Scientific Research Center, Cali, Colombia. aalvarez@inmuno.org.
authors.forename: Álvaro
authors.initials: Á
authors.lastname: Álvarez
authors.affiliation: Malaria Vaccine and Drug Development Centre, Cali, Colombia. jpquintero84@gmail.com.
authors.forename: Juan Pablo
authors.initials: JP
authors.lastname: Quintero
authors.affiliation: Ministry of Health and Social Protection of Colombia, Bogotá, Colombia. jpadilla@minsalud.gov.co.
authors.forename: Julio
authors.initials: J
authors.lastname: Padilla
authors.affiliation: Caucaseco Scientific Research Center, Cali, Colombia. marevalo@inmuno.org.|Latin American Center for Malaria Research, Cali, Colombia. marevalo@inmuno.org.|School of Health, Universidad del Valle, Cali, Colombia. marevalo@inmuno.org.
authors.forename: Myriam
authors.initials: M
authors.lastname: Arévalo-Herrera
authors.affiliation: Caucaseco Scientific Research Center, Cali, Colombia. sherrera@inmuno.org.|Latin American Center for Malaria Research, Cali, Colombia. sherrera@inmuno.org.
authors.forename: Sócrates
authors.initials: S
authors.lastname: Herrera
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D058345:Asymptomatic Infections / Q000453:epidemiology*; D002648:Child; D002675:Child, Preschool; D003105:Colombia / Q000453:epidemiology; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D016778:Malaria, Falciparum / Q000453:epidemiology* / Q000469:parasitology; D016780:Malaria, Vivax / Q000453:epidemiology / Q000469:parasitology; D008297:Male; D008875:Middle Aged; D010963:Plasmodium falciparum / Q000302:isolation & purification*; D010966:Plasmodium vivax / Q000302:isolation & purification*; D015995:Prevalence; D060888:Real-Time Polymerase Chain Reaction; D055815:Young Adult