Use of different transmission metrics to describe malaria epidemiology in the highlands of western Kenya.
BACKGROUND
Monitoring and evaluation of malaria programmes may require a combination of approaches to detect any effects of control. This is particularly true at lower transmission levels where detecting both infection and exposure to infection will provide additional evidence of any change. This paper describes use of three transmission metrics to explore the malaria epidemiology in the highlands of western Kenya.


METHODS
A malariometric survey was conducted in June 2009 in two highland districts, Kisii and Rachuonyo South, Nyanza Province, Kenya using a cluster design. Enumeration areas were used to sample 46 clusters from which 12 compounds were randomly sampled. Individuals provided a finger-blood sample to assess malaria infection (rapid diagnostic test, PCR) and exposure (anti-Plasmodium falciparum MSP-1 antibodies) and a questionnaire was administered to record household factors and assess use of vector control interventions.


RESULTS
Malaria prevalence infection rates were 3.0 % (95 % CI 2.2-4.2 %) by rapid diagnostic test (RDT) and 8.5 % (95 % CI 7.0-10.4 %) by PCR and these ranged from 0-13.1 to 0-14.8 % between clusters for RDT and PCR, respectively. Seroprevalence was 36.8 % (95 % CI 33.9-39.8) ranging from 18.6 to 65.8 %. Both RDT and PCR prevalences were highest in children aged 5-10 years but the proportion of infections that were sub-patent was highest in those between 15 and 20 years of age (78.1 %, 95 % CI 63.0-93.3 %) and those greater than 20 years (73.3 %, 95 % CI 64.5-81.9 %). Those reporting both indoor residual spraying (IRS) in their home and use of bed nets had lower exposure to malaria compared to those who reported using IRS or bed nets alone.


CONCLUSIONS
In this highland site in western Kenya malaria transmission was low, but highly heterogeneous. To accurately characterize the true extent of malaria transmission, more sensitive and complementary metrics such as PCR or serology are required in addition to the standard microscopy and/or RDTs that are routinely used. This is likely to be the case in other low endemicity settings.
Department of Disease Control, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, UK. jennyc.stevenson@macharesearch.org.|Johns Hopkins Bloomberg School of Public Health, 615 North Wolfe St, Baltimore, MD, 21205, USA. jennyc.stevenson@macharesearch.org.
Jennifer C
JC
Stevenson
Department of Immunology and Infection, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, UK. gillian.stresman@lshtm.ac.uk.
Gillian H
GH
Stresman
Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands. amrish.baidjoe@gmail.com.
Amrish
A
Baidjoe
Kenya Medical Research Institute, Centre for Global Health Research, Kisumu, Kenya. battyokoth@yahoo.com.
Albert
A
Okoth
Kenya Medical Research Institute, Centre for Global Health Research, Kisumu, Kenya. robinmigiro@rocketmail.com.
Robin
R
Oriango
Kenya Medical Research Institute, Centre for Global Health Research, Kisumu, Kenya. cowaga@gmail.com.
Chrispin
C
Owaga
Kenya Medical Research Institute, Centre for Global Health Research, Kisumu, Kenya. emarube@kemricdc.org.
Elizabeth
E
Marube
Department of Disease Control, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, UK. teun.bousema@lshtm.ac.uk.|Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands. teun.bousema@lshtm.ac.uk.
Teun
T
Bousema
Department of Disease Control, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, UK. jonathan.cox@lshtm.ac.uk.
Jonathan
J
Cox
Department of Immunology and Infection, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, UK. chris.drakeley@lshtm.ac.uk.
Chris
C
Drakeley
D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D002846:Chromatography, Affinity; D019411:Clinical Laboratory Techniques / Q000379:methods*; D018562:Disease Transmission, Infectious; D004812:Epidemiologic Methods; D005260:Female; D006801:Humans; D007223:Infant; D007630:Kenya / Q000453:epidemiology; D016778:Malaria, Falciparum / Q000175:diagnosis / Q000453:epidemiology* / Q000635:transmission*; D008297:Male; D016133:Polymerase Chain Reaction; D015995:Prevalence; D011795:Surveys and Questionnaires; D055815:Young Adult