title: Spatial patterns of incident malaria cases and their household contacts in a single clinic catchment area of Chongwe District, Zambia.
abstract: BACKGROUND
  Reactive case detection (RACD) for malaria is a strategy that may be used to complement passive surveillance, as passive surveillance fails to identify infections that are asymptomatic or do not seek care. The spatial and seasonal patterns of incident (index) cases reported at a single clinic in Chongwe District were explored.
  
  
  METHODS
  A RACD strategy was implemented from June 2012 to June 2013 in a single catchment area in Chongwe District. Incident (index) cases recorded at the clinic were followed up at their household, and all household contacts were tested for malaria using rapid diagnostic tests (RDTs). GPS coordinates were taken at each index household. Spatial analyses were conducted to assess characteristics related to clustering, cluster detection and spatial variation in risk of index houses. Effects of season (rainy versus dry), distance to the clinic and distance to the main road were considered as modifying factors. Lastly, logistic regression was used to identify factors associated with the proportion of household contacts testing RDT positive.
  
  
  RESULTS
  A total of 426 index households were enrolled, with 1,621 household contacts (45% RDT positive). Two space-time clusters were identified in the rainy season, with ten times and six times higher risk than expected. Significantly increased spatial clustering of index households was found in the rainy season as compared to the dry season (based on K-function methodology). However, no seasonal difference in mapped spatial intensity of index households was identified. Logistic regression analysis identified two main factors associated with a higher proportion of RDT positive household contacts. There was a 41% increased odds of RDT positive household contacts in households where the index case was under 5 years of age [OR = 1.41, 95% confidence intervals (1.15, 1.73)]. For every 500-m increase in distance from the road, there was a 5% increased odds of RDT positive household contacts [OR = 1.05 (1.02, 1.07)], controlling for season.
  
  
  CONCLUSIONS
  Areas of increased report of malaria persist after controlling for distance to the clinic and main road. Clinic-based interventions will miss asymptomatic, non-care seeking infections located farther from the road. RACD may identify additional infections missed at the clinic.
authors.affiliation: Department of Epidemiology, Johns Hopkins University Bloomberg School of Public Health, 615 N Wolfe St, Baltimore, MD, 21205, USA. Jpinchoff@gmail.com.
authors.forename: Jessie
authors.initials: J
authors.lastname: Pinchoff
authors.affiliation: Centre for Infectious Disease Research Zambia, 5032 Great North Road, Lusaka, Zambia. germanh@uab.edu.|University of Alabama at Birmingham, 1900 University Boulevard, Birmingham, AL, 35294, USA. germanh@uab.edu.
authors.forename: German
authors.initials: G
authors.lastname: Henostroza
authors.affiliation: Icahn School of Medicine at Mt Sinai, 1428 Madison Avenue, New York, NY, 10029, USA. bryan.carter@mssm.edu.
authors.forename: Bryan S
authors.initials: BS
authors.lastname: Carter
authors.affiliation: Department of Epidemiology, University of Washington School of Public Health, Box 357236, Seattle, WA, 98165, USA. str24@uw.edu.
authors.forename: Sarah T
authors.initials: ST
authors.lastname: Roberts
authors.affiliation: Centre for Infectious Disease Research Zambia, 5032 Great North Road, Lusaka, Zambia. Sisa.Hatwiinda@cidrz.org.
authors.forename: Sisa
authors.initials: S
authors.lastname: Hatwiinda
authors.affiliation: Ministry of Health, National Malaria Control Centre, Chainama Hospital, College Grounds, Off Great East Road, PO Box 32509, Lusaka, Zambia. Bossbusk@gmail.com.
authors.forename: Busiku
authors.initials: B
authors.lastname: Hamainza
authors.affiliation: Ministry of Health, National Malaria Control Centre, Chainama Hospital, College Grounds, Off Great East Road, PO Box 32509, Lusaka, Zambia. mhawela@yahoo.co.uk.
authors.forename: Moonga
authors.initials: M
authors.lastname: Hawela
authors.affiliation: Department of Epidemiology, Johns Hopkins University Bloomberg School of Public Health, 615 N Wolfe St, Baltimore, MD, 21205, USA. fcurriero@jhu.edu.
authors.forename: Frank C
authors.initials: FC
authors.lastname: Curriero
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002675:Child, Preschool; D016000:Cluster Analysis; D005191:Family Characteristics; D005260:Female; D006801:Humans; D015994:Incidence; D007223:Infant; D007231:Infant, Newborn; D008288:Malaria / Q000453:epidemiology* / Q000469:parasitology; D008297:Male; D008875:Middle Aged; D012307:Risk Factors; D012621:Seasons; D062206:Spatial Analysis; D055815:Young Adult; D015024:Zambia / Q000453:epidemiology