title: High prevalence and spatial distribution of Strongyloides stercoralis in rural Cambodia.
abstract: BACKGROUND
  The threadworm, Strongyloides stercoralis, endemic in tropical and temperate climates, is a neglected tropical disease. Its diagnosis requires specific methods, and accurate information on its geographic distribution and global burden are lacking. We predicted prevalence, using Bayesian geostatistical modeling, and determined risk factors in northern Cambodia.
  
  
  METHODS
  From February to June 2010, we performed a cross-sectional study among 2,396 participants from 60 villages in Preah Vihear Province, northern Cambodia. Two stool specimens per participant were examined using Koga agar plate culture and the Baermann method for detecting S. stercoralis infection. Environmental data was linked to parasitological and questionnaire data by location. Bayesian mixed logistic models were used to explore the spatial correlation of S. stercoralis infection risk. Bayesian Kriging was employed to predict risk at non-surveyed locations.
  
  
  RESULTS
  Of the 2,396 participants, 44.7% were infected with S. stercoralis. Of 1,071 strongyloidiasis cases, 339 (31.6%) were among schoolchildren and 425 (39.7%) were found in individuals under 16 years. The incidence of S. stercoralis infection statistically increased with age. Infection among male participants was significantly higher than among females (OR: 1.7; 95% CI: 1.4-2.0; P<0.001). Participants who defecated in latrines were infected significantly less than those who did not (OR: 0.6; 95% CI: 0.4-0.8; P=0.001). Strongyloidiasis cases would be reduced by 39% if all participants defecated in latrines. Incidence of S. stercoralis infections did not show a strong tendency toward spatial clustering in this province. The risk of infection significantly decreased with increasing rainfall and soil organic carbon content, and increased in areas with rice fields.
  
  
  CONCLUSIONS
  Prevalence of S. stercoralis in rural Cambodia is very high and school-aged children and adults over 45 years were the most at risk for infection. Lack of access to adequate treatment for chronic uncomplicated strongyloidiasis is an urgent issue in Cambodia. We would expect to see similar prevalence rates elsewhere in Southeast Asia and other tropical resource poor countries.
authors.affiliation: National Centre for Parasitology, Entomology and Malaria Control, Ministry of Health, Phnom Penh, Cambodia; Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, Basel, Switzerland; University of Basel, Basel, Switzerland.
authors.forename: Virak
authors.initials: V
authors.lastname: Khieu
authors.affiliation: Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, Basel, Switzerland; University of Basel, Basel, Switzerland.
authors.forename: Fabian
authors.initials: F
authors.lastname: Schär
authors.affiliation: Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, Basel, Switzerland; University of Basel, Basel, Switzerland.
authors.forename: Armelle
authors.initials: A
authors.lastname: Forrer
authors.affiliation: Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, Basel, Switzerland; University of Basel, Basel, Switzerland.
authors.forename: Jan
authors.initials: J
authors.lastname: Hattendorf
authors.affiliation: University of Basel, Basel, Switzerland; Medical Department and Diagnostics, Swiss Tropical and Public Health Institute, Basel, Switzerland.
authors.forename: Hanspeter
authors.initials: H
authors.lastname: Marti
authors.affiliation: National Centre for Parasitology, Entomology and Malaria Control, Ministry of Health, Phnom Penh, Cambodia.
authors.forename: Socheat
authors.initials: S
authors.lastname: Duong
authors.affiliation: Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, Basel, Switzerland; University of Basel, Basel, Switzerland.
authors.forename: Penelope
authors.initials: P
authors.lastname: Vounatsou
authors.affiliation: National Centre for Parasitology, Entomology and Malaria Control, Ministry of Health, Phnom Penh, Cambodia.
authors.forename: Sinuon
authors.initials: S
authors.lastname: Muth
authors.affiliation: Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, Basel, Switzerland; University of Basel, Basel, Switzerland.
authors.forename: Peter
authors.initials: P
authors.lastname: Odermatt
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D002160:Cambodia / Q000453:epidemiology; D002648:Child; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D005243:Feces / Q000469:parasitology; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D018570:Risk Assessment; D012424:Rural Population; D017171:Strongyloides stercoralis / Q000302:isolation & purification*; D013322:Strongyloidiasis / Q000453:epidemiology* / Q000469:parasitology; D011795:Surveys and Questionnaires; D019371:Topography, Medical; D055815:Young Adult