title: Epidemiology of Plasmodium knowlesi malaria in north-east Sabah, Malaysia: family clusters and wide age distribution.
abstract: BACKGROUND
  The simian parasite Plasmodium knowlesi is a common cause of human malaria in Malaysian Borneo, with a particularly high incidence in Kudat, Sabah. Little is known however about the epidemiology in this substantially deforested region.
  
  
  METHODS
  Malaria microscopy records at Kudat District Hospital were retrospectively reviewed from January 2009-November 2011. Demographics, and PCR results if available, were recorded for each positive result. Medical records were reviewed for patients suspected of representing family clusters, and families contacted for further information. Rainfall data were obtained from the Malaysian Meteorological Department.
  
  
  RESULTS
  "Plasmodium malariae" mixed or mono-infection was diagnosed by microscopy in 517/653 (79%) patients. Of these, PCR was performed in 445 (86%) and was positive for P. knowlesi mono-infection in 339 (76%). Patients with knowlesi malaria demonstrated a wide age distribution (median 33, IQR 20-50, range 0.7-89 years) with P. knowlesi predominating in all age groups except those <5 years old, where numbers approximated those of Plasmodium falciparum and Plasmodium vivax. Two contemporaneous family clusters were identified: a father with two children (aged 10-11 years); and three brothers (aged one-11 years), all with PCR-confirmed knowlesi malaria. Cases of P. knowlesi demonstrated significant seasonal variation, and correlated with rainfall in the preceding three to five months.
  
  
  CONCLUSIONS
  Plasmodium knowlesi is the most common cause of malaria admissions to Kudat District Hospital. The wide age distribution and presence of family clusters suggest that transmission may be occurring close to or inside people's homes, in contrast to previous reports from densely forested areas of Sarawak. These findings have significant implications for malaria control. Prospective studies of risk factors, vectors and transmission dynamics of P. knowlesi in Sabah, including potential for human-to-human transmission, are needed.
authors.affiliation: Global Health Division, Menzies School of Health Research, PO Box 41096, Casuarina 0810,, Northern Territory, Australia.
authors.forename: Bridget E
authors.initials: BE
authors.lastname: Barber
authors.forename: Timothy
authors.initials: T
authors.lastname: William
authors.forename: Prabakaran
authors.initials: P
authors.lastname: Dhararaj
authors.forename: Fread
authors.initials: F
authors.lastname: Anderios
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Grigg
authors.forename: Tsin W
authors.initials: TW
authors.lastname: Yeo
authors.forename: Nicholas M
authors.initials: NM
authors.lastname: Anstey
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D016000:Cluster Analysis; D005192:Family Health; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008288:Malaria / Q000453:epidemiology* / Q000469:parasitology*; D008296:Malaysia / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D016790:Plasmodium knowlesi / Q000302:isolation & purification*; D012189:Retrospective Studies; D055815:Young Adult