title: Hydrological Regime and Water Shortage as Drivers of the Seasonal Incidence of Diarrheal Diseases in a Tropical Montane Environment.
abstract: The global burden of diarrhea is a leading cause of morbidity and mortality worldwide. In montane areas of South-East Asia such as northern Laos, recent changes in land use have induced increased runoff, soil erosion and in-stream suspended sediment loads, and potential pathogen dissemination. To our knowledge, few studies have related diarrhea incidences to catchment scale hydrological factors such as river discharge, and loads of suspended sediment and of Fecal Indicator Bacteria (FIB) such as Escherichia coli, together with sociological factors such as hygiene practices. We hypothesized that climate factors combined with human behavior control diarrhea incidence, either because higher rainfall, leading to higher stream discharges, suspended sediment loads and FIB counts, are associated with higher numbers of reported diarrhea cases during the rainy season, or because water shortage leads to the use of less safe water sources during the dry season. Using E. coli as a FIB, the objectives of this study were thus (1) to characterize the epidemiological dynamics of diarrhea in Northern Laos, and (2) to identify which hydro-meteorological and sociological risk factors were associated with diarrhea epidemics.
  
  
  
  Considering two unconnected river catchments of 22 and 7,448 km2, respectively, we conducted a retrospective time series analysis of meteorological variables (rainfall, air temperature), hydrological variables (discharge, suspended sediments, FIB counts, water temperature), and the number of diarrheal disease cases reported at 6 health centers located in the 5 southern districts of the Luang Prabang Province, Lao PDR. We also examined the socio-demographic factors potentially affecting vulnerability to the effect of the climate factors, such as drinking water sources, hygiene habits, and recreational water exposure.
  
  
  
  Using thus a mixed methods approach, we found E. coli to be present all year long (100-1,000 Most Probable Number or MPN 100 mL-1) indicating that fecal contamination is ubiquitous and constant. We found that populations switch their water supply from wells to surface water during drought periods, the latter of which appear to be at higher risk of bacterial contamination than municipal water fountains. We thus found that water shortage in the Luang Prabang area triggers diarrhea peaks during the dry and hot season and that rainfall and aquifer refill ends the epidemic during the wet season. The temporal trends of reported daily diarrhea cases were generally bimodal with hospital admissions peaking in February-March and later in May-July. Annual incidence rates were higher in more densely populated areas and mostly concerned the 0-4 age group and male patients.
  
  
  
  We found that anthropogenic drivers, such as hygiene practices, were at least as important as environmental drivers in determining the seasonal pattern of a diarrhea epidemic. For diarrheal disease risk monitoring, discharge or groundwater level can be considered as relevant proxies. These variables should be monitored in the framework of an early warning system provided that a tradeoff is found between the size of the monitored catchment and the frequency of the measurement.
authors.affiliation: Géosciences Environnement Toulouse, Université de Toulouse, CNES, CNRS, IRD, UPS, Toulouse, France.
authors.forename: Laurie
authors.identifier: 0000-0003-3414-7329
authors.initials: L
authors.lastname: Boithias
authors.affiliation: MIVEGEC (UMR CNRS-IRD-University of Montpellier), Montpellier, France.|Oxford University Clinical Research Unit, Hanoi, Vietnam.
authors.forename: Marc
authors.initials: M
authors.lastname: Choisy
authors.affiliation: Institut de la Francophonie pour la Médecine Tropicale (IFMT), Vientiane, Lao PDR.
authors.forename: Noy
authors.initials: N
authors.lastname: Souliyaseng
authors.affiliation: Irstea Montpellier, Montpellier, France.
authors.forename: Marine
authors.initials: M
authors.lastname: Jourdren
authors.affiliation: Institut de la Francophonie pour la Médecine Tropicale (IFMT), Vientiane, Lao PDR.
authors.forename: Fabrice
authors.initials: F
authors.lastname: Quet
authors.affiliation: Institut de la Francophonie pour la Médecine Tropicale (IFMT), Vientiane, Lao PDR.
authors.forename: Yves
authors.initials: Y
authors.lastname: Buisson
authors.affiliation: IRD, Department of Agricultural Land Management (DALaM), Ban Nogviengkham, Xaythany District, Vientiane, Lao PDR.
authors.forename: Chanthamousone
authors.initials: C
authors.lastname: Thammahacksa
authors.affiliation: IRD-iEES-Paris, Department of Agricultural Land Management (DALaM), Ban Nogviengkham, Xaythany District, Vientiane, Lao PDR.|iEES-Paris (IRD-Sorbonne Universités-UPMC-CNRS-INRA-UDD-UPEC), Université Pierre et Marie Curie (UPMC), 4 place Jussieu, Paris, France.
authors.forename: Norbert
authors.initials: N
authors.lastname: Silvera
authors.affiliation: IRD, Department of Agricultural Land Management (DALaM), Ban Nogviengkham, Xaythany District, Vientiane, Lao PDR.
authors.forename: Keooudone
authors.initials: K
authors.lastname: Latsachack
authors.affiliation: Department of Agricultural Land Management (DALaM), Ban Nogviengkham, Xaythany District, Vientiane, Lao PDR.
authors.forename: Oloth
authors.initials: O
authors.lastname: Sengtaheuanghoung
authors.affiliation: IRD-iEES-Paris, Department of Agricultural Land Management (DALaM), Ban Nogviengkham, Xaythany District, Vientiane, Lao PDR.|iEES-Paris (IRD-Sorbonne Universités-UPMC-CNRS-INRA-UDD-UPEC), Université Pierre et Marie Curie (UPMC), 4 place Jussieu, Paris, France.
authors.forename: Alain
authors.initials: A
authors.lastname: Pierret
authors.affiliation: iEES-Paris (IRD-Sorbonne Universités-UPMC-CNRS-INRA-UDD-UPEC), Université Pierre et Marie Curie (UPMC), 4 place Jussieu, Paris, France.
authors.forename: Emma
authors.initials: E
authors.lastname: Rochelle-Newall
authors.affiliation: Géosciences Environnement Toulouse, Université de Toulouse, CNES, CNRS, IRD, UPS, Toulouse, France.
authors.forename: Sylvia
authors.initials: S
authors.lastname: Becerra
authors.affiliation: Géosciences Environnement Toulouse, Université de Toulouse, CNES, CNRS, IRD, UPS, Toulouse, France.
authors.forename: Olivier
authors.initials: O
authors.lastname: Ribolzi
mesh_terms: D003151:Community Health Centers; D003710:Demography; D003967:Diarrhea / Q000453:epidemiology* / Q000382:microbiology / Q000517:prevention & control; D058872:Epidemics; D004926:Escherichia coli / Q000302:isolation & purification; D005243:Feces / Q000382:microbiology*; D005260:Female; D006801:Humans; D006920:Hygiene; D007812:Laos / Q000453:epidemiology; D008297:Male; D011891:Rain; D012189:Retrospective Studies; D045483:Rivers / Q000382:microbiology; D012621:Seasons; D014329:Tropical Climate; D014867:Water; D014871:Water Microbiology; D014881:Water Supply
chemical_list: D014867:Water