title: Ascaris lumbricoides infection and its relation to environmental factors in the Mbeya region of Tanzania, a cross-sectional, population-based study.
abstract: BACKGROUND
  With one quarter of the world population infected, the intestinal nematode Ascaris lumbricoides is one of the most common infectious agents, especially in the tropics and sub-tropics. Infection is caused by oral intake of eggs and can cause respiratory and gastrointestinal problems. To identify high risk areas for intervention, it is necessary to understand the effects of climatic, environmental and socio-demographic conditions on A. lumbricoides infection.
  
  
  METHODS
  Cross-sectional survey data of 6,366 study participants in the Mbeya region of South-Western Tanzania were used to analyze associations between remotely sensed environmental data and A. lumbricoides infection. Non-linear associations were accounted for by using fractional polynomial regression, and socio-demographic and sanitary data were included as potential confounders.
  
  
  RESULTS
  The overall prevalence of A. lumbricoides infection was 6.8%. Our final multivariable model revealed a significant non-linear association between rainfall and A. lumbricoides infection with peak prevalences at 1740 mm of mean annual rainfall. Mean annual land surface temperature during the day was linearly modeled and negatively associated with A. lumbricoides infection (odds ratio (OR) = 0.87, 95% confidence interval (CI) = 0.78-0.97). Furthermore, age, which also showed a significant non-linear association (infection maximum at 7.7 years), socio-economic status (OR = 0.82, CI = 0.68-0.97), and latrine coverage around the house (OR = 0.80, CI = 0.67-0.96) remained in the final model.
  
  
  CONCLUSIONS
  A. lumbricoides infection was associated with environmental, socio-demographic and sanitary factors both in uni- and multivariable analysis. Non-linear analysis with fractional polynomials can improve model fit, resulting in a better understanding of the relationship between environmental conditions and helminth infection, and more precise predictions of high prevalence areas. However, socio-demographic determinants and sanitary conditions should also be considered, especially when planning public health interventions on a smaller scale, such as the community level.
authors.affiliation: Division of Infectious Diseases and Tropical Medicine, Medical Center of the University of Munich (LMU), Munich, Germany; Institute for Medical Bioinformatics, Biometry, and Epidemiology, Ludwig-Maximilians-University, Munich, Germany; Department of Social Epidemiology, Institute for Public Health and Nursing Research, University of Bremen, Bremen, Germany.
authors.forename: Steffen Andreas
authors.initials: SA
authors.lastname: Schüle
authors.affiliation: NIMR-Mbeya Medical Research Center (MMRC), Mbeya, Tanzania.
authors.forename: Petra
authors.initials: P
authors.lastname: Clowes
authors.affiliation: Division of Infectious Diseases and Tropical Medicine, Medical Center of the University of Munich (LMU), Munich, Germany; NIMR-Mbeya Medical Research Center (MMRC), Mbeya, Tanzania.
authors.forename: Inge
authors.initials: I
authors.lastname: Kroidl
authors.affiliation: NIMR-Mbeya Medical Research Center (MMRC), Mbeya, Tanzania.
authors.forename: Dickens O
authors.initials: DO
authors.lastname: Kowuor
authors.affiliation: NIMR-Mbeya Medical Research Center (MMRC), Mbeya, Tanzania.
authors.forename: Anthony
authors.initials: A
authors.lastname: Nsojo
authors.affiliation: NIMR-Mbeya Medical Research Center (MMRC), Mbeya, Tanzania.
authors.forename: Chacha
authors.initials: C
authors.lastname: Mangu
authors.affiliation: Division of Infectious Diseases and Tropical Medicine, Medical Center of the University of Munich (LMU), Munich, Germany; Institute for Medical Bioinformatics, Biometry, and Epidemiology, Ludwig-Maximilians-University, Munich, Germany.
authors.forename: Helene
authors.initials: H
authors.lastname: Riess
authors.affiliation: Division of Infectious Diseases and Tropical Medicine, Medical Center of the University of Munich (LMU), Munich, Germany; German Center for Infection Research (DZIF), partner site Munich, Munich, Germany.
authors.forename: Christof
authors.initials: C
authors.lastname: Geldmacher
authors.affiliation: Institute for Medical Bioinformatics, Biometry, and Epidemiology, Ludwig-Maximilians-University, Munich, Germany.
authors.forename: Rüdiger Paul
authors.initials: RP
authors.lastname: Laubender
authors.affiliation: Mbeya Regional Medical Office, Mbeya, Tanzania.
authors.forename: Seif
authors.initials: S
authors.lastname: Mhina
authors.affiliation: NIMR-Mbeya Medical Research Center (MMRC), Mbeya, Tanzania.
authors.forename: Leonard
authors.initials: L
authors.lastname: Maboko
authors.affiliation: Division of Infectious Diseases and Tropical Medicine, Medical Center of the University of Munich (LMU), Munich, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Löscher
authors.affiliation: Division of Infectious Diseases and Tropical Medicine, Medical Center of the University of Munich (LMU), Munich, Germany; NIMR-Mbeya Medical Research Center (MMRC), Mbeya, Tanzania; German Center for Infection Research (DZIF), partner site Munich, Munich, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Hoelscher
authors.affiliation: Division of Infectious Diseases and Tropical Medicine, Medical Center of the University of Munich (LMU), Munich, Germany; German Center for Infection Research (DZIF), partner site Munich, Munich, Germany.
authors.forename: Elmar
authors.initials: E
authors.lastname: Saathoff
mesh_terms: D000293:Adolescent; D000328:Adult; D000704:Analysis of Variance; D000818:Animals; D001196:Ascariasis / Q000453:epidemiology* / Q000469:parasitology / Q000635:transmission; D017164:Ascaris lumbricoides / Q000502:physiology*; D002648:Child; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D015995:Prevalence; D011891:Rain; D012959:Socioeconomic Factors; D013636:Tanzania / Q000453:epidemiology; D013696:Temperature