Time activity patterns in exposure assessment: the case of livestock related infections

Summary Between 2007 and 2010 the Netherlands experienced the largest documented Q fever outbreak to date. This outbreak and several other incidents with infectious disease spill-overs from livestock to humans, initiated research focussing on the impact on human health of living in the vicinity of livestock farms. In this thesis, information about outdoor activities -mobility and activities outdoors near the home- were collected using GPS logging and self-reporting, in a rural population in the Netherlands. This was performed to include a measure for duration and frequency of exposure to exposure assessment methods for livestock related infections. Outdoor activity patterns were combined with data about livestock farms in the research area, which acted as exposure source. Time spent outdoors close to home in the presence of goat farms translated into an increased pneumonia risk. The specific agent or mechanism underlying this increased risk for pneumonia was not identified and is currently under study. Mobility outdoors in the vicinity of goat farms did not markedly change risk estimates, but this might be expected given that the time spent on active mobility was relatively limited. Still, it was observed that outdoor exposure, a combination of time spent outdoors near the home and active mobility, contributed to the risk of becoming C. burnetii serology positive during the 2007-2010 Dutch Q fever outbreak. These associations were stronger if people lived closer to C. burnetii positive farms. Given these findings, time activity patterns, when included to exposure assessment, provided somewhat stronger associations, than for measures earlier used in spatial epidemiological studies such as home distance from the source. Time spent in the vicinity of an emitting infectious source is likely to play a role in exposure assessment to livestock related zoonotic pathogens and information about time activity data should therefore be considered for exposure assessment methods. The method how to include this factor is a topic for further study. It was shown that study participants significantly overestimated their time spent outdoors in active transport when self-reported data were compared to GPS measured data, but several general characteristics correlating to differences in mobility patterns were identified. Using this information, three different approaches were designed to predict active mobility for exposure assessment. These estimation methods however, were equally unable to accurately predict active mobility, when compared to matching GPS data. Measurements therefore, still represent the best possible tool to evaluate outdoor activity and active mobility. Given the identified associations in this thesis, in the event of a future livestock related outbreak of a zoonotic disease, depending on the causal pathogen, active mobility and outdoors activities should be limited in the vicinity of infected farms. Among residents living near future infected farms, health and time-activity data should be collected, this will provide additional data that may strengthen the findings in this thesis

Pesticide use and practice of local farmers in the Central Rift Valley (CRV) of Ethiopia: implications for the environment and health hazards

In this study, pesticide practices and related environmental and health effects were investigated in the Central Rift Valley (CRV) of Ethiopia through a farmers’ survey. Questionnaires were distributed to 422 local farmers in the Arsi-Negele, Meki and Ziway areas. Multiple linear regression analyses were used to evaluate the results of the questionnaire and to identify risk factors associated with environmental and health effects after spraying. The majority of the farmers (44.4–55.0%) stored their pesticides in the kitchen or anywhere in the house, while only 6.5–32.0% of the farmers stored them in a separate place outside the house. A large majority of the farmers (63%) did not use personal protective equipment during pesticide spraying and handling, which was negatively associated with understanding pesticide instructions of the pesticide labels, OR: 0.9; (95% CI:0.82–0.98) in the supervised stepwise backwards selection model. Reading the instructions of the pesticide labels was positively associated with understanding instructions OR: 1.59 (95% CI: 1.0–2.54). The risk for water pollution was higher in the Meki region OR: 1.26 (95% CI: 1.14–1.4) compared to Ziway and Arsi-Negele. Most farmers (66%) experienced discomfort after pesticide spraying and Illnesses from pesticide spraying were more frequently reported by educated farmers. Therefore, proper training in pesticide use in this region could strongly reduce the health risk associated with pesticide exposure

Human-livestock contacts and their relationship to transmission of zoonotic pathogens, a systematic review of literature

Background: Micro-organisms transmitted from vertebrate animals - including livestock - to humans account for an estimated 60% of human pathogens. Micro-organisms can be transmitted through inhalation, ingestion, via conjunctiva or physical contact. Close contact with animals is crucial for transmission. The role of intensity and type of contact patterns between livestock and humans for disease transmission is poorly understood. In this systematic review we aimed to summarise current knowledge regarding patterns of human-livestock contacts and their role in micro-organism transmission. Methods: We included peer-reviewed publications published between 1996 and 2014 in our systematic review if they reported on human-livestock contacts, human cases of livestock-related zoonotic diseases or serological epidemiology of zoonotic diseases in human samples. We extracted any information pertaining the type and intensity of human-livestock contacts and associated zoonoses. Results: 1522 papers were identified, 75 were included: 7 reported on incidental zoonoses after brief animal-human contacts (e.g. farm visits), 10 on environmental exposures and 15 on zoonoses in developing countries where backyard livestock keeping is still customary. 43 studies reported zoonotic risks in different occupations. Occupations at risk included veterinarians, culling personnel, slaughterhouse workers and farmers. For culling personnel, more hours exposed to livestock resulted in more frequent occurrence of transmission. Slaughterhouse workers in contact with live animals were more often positive for zoonotic micro-organisms compared to co-workers only exposed to carcasses. Overall, little information was available about the actual mode of micro-organism transmission. Conclusions: Little is known about the intensity and type of contact patterns between livestock and humans that result in micro-organism transmission. Studies performed in occupational settings provide some, but limited evidence of exposure response-like relationships for livestock-human contact and micro-organism transmission. Better understanding of contact patterns driving micro-organism transmission from animals to humans is needed to provide options for prevention and thus deserves more attention

Human-livestock contacts and their relationship to transmission of zoonotic pathogens, a systematic review of literature

BACKGROUND: Micro-organisms transmitted from vertebrate animals - including livestock - to humans account for an estimated 60% of human pathogens. Micro-organisms can be transmitted through inhalation, ingestion, via conjunctiva or physical contact. Close contact with animals is crucial for transmission. The role of intensity and type of contact patterns between livestock and humans for disease transmission is poorly understood. In this systematic review we aimed to summarise current knowledge regarding patterns of human-livestock contacts and their role in micro-organism transmission. METHODS: We included peer-reviewed publications published between 1996 and 2014 in our systematic review if they reported on human-livestock contacts, human cases of livestock-related zoonotic diseases or serological epidemiology of zoonotic diseases in human samples. We extracted any information pertaining the type and intensity of human-livestock contacts and associated zoonoses. RESULTS: 1522 papers were identified, 75 were included: 7 reported on incidental zoonoses after brief animal-human contacts (e.g. farm visits), 10 on environmental exposures and 15 on zoonoses in developing countries where backyard livestock keeping is still customary. 43 studies reported zoonotic risks in different occupations. Occupations at risk included veterinarians, culling personnel, slaughterhouse workers and farmers. For culling personnel, more hours exposed to livestock resulted in more frequent occurrence of transmission. Slaughterhouse workers in contact with live animals were more often positive for zoonotic micro-organisms compared to co-workers only exposed to carcasses. Overall, little information was available about the actual mode of micro-organism transmission. CONCLUSIONS: Little is known about the intensity and type of contact patterns between livestock and humans that result in micro-organism transmission. Studies performed in occupational settings provide some, but limited evidence of exposure response-like relationships for livestock-human contact and micro-organism transmission. Better understanding of contact patterns driving micro-organism transmission from animals to humans is needed to provide options for prevention and thus deserves more attention

Prediction of human active mobility in rural areas: development and validity tests of three different approaches

BACKGROUND/AIM: Active mobility may play a relevant role in the assessment of environmental exposures (e.g. traffic-related air pollution, livestock emissions), but data about actual mobility patterns are work intensive to collect, especially in large study populations, therefore estimation methods for active mobility may be relevant for exposure assessment in different types of studies. We previously collected mobility patterns in a group of 941 participants in a rural setting in the Netherlands, using week-long GPS tracking. We had information regarding personal characteristics, self-reported data regarding weekly mobility patterns and spatial characteristics. The goal of this study was to develop versatile estimates of active mobility, test their accuracy using GPS measurements and explore the implications for exposure assessment studies. METHODS: We estimated hours/week spent on active mobility based on personal characteristics (e.g. age, sex, pre-existing conditions), self-reported data (e.g. hours spent commuting per bike) or spatial predictors such as home and work address. Estimated hours/week spent on active mobility were compared with GPS measured hours/week, using linear regression and kappa statistics. RESULTS: Estimated and measured hours/week spent on active mobility had low correspondence, even the best predicting estimation method based on self-reported data, resulted in a R2 of 0.09 and Cohen's kappa of 0.07. A visual check indicated that, although predicted routes to work appeared to match GPS measured tracks, only a small proportion of active mobility was captured in this way, thus resulting in a low validity of overall predicted active mobility. CONCLUSIONS: We were unable to develop a method that could accurately estimate active mobility, the best performing method was based on detailed self-reported information but still resulted in low correspondence. For future studies aiming to evaluate the contribution of home-work traffic to exposure, applying spatial predictors may be appropriate. Measurements still represent the best possible tool to evaluate mobility patterns

Mobility assessment of a rural population in the Netherlands using GPS measurements

The home address is a common spatial proxy for exposure assessment in epidemiological studies but mobility may introduce exposure misclassification. Mobility can be assessed using self-reports or objectively measured using GPS logging but self-reports may not assess the same information as measured mobility. We aimed to assess mobility patterns of a rural population in the Netherlands using GPS measurements and self-reports and to compare GPS measured to self-reported data, and to evaluate correlates of differences in mobility patterns. In total 870 participants filled in a questionnaire regarding their transport modes and carried a GPS-logger for 7 consecutive days. Transport modes were assigned to GPS-tracks based on speed patterns. Correlates of measured mobility data were evaluated using multiple linear regression. We calculated walking, biking and motorised transport durations based on GPS and self-reported data and compared outcomes. We used Cohen's kappa analyses to compare categorised self-reported and GPS measured data for time spent outdoors. Self-reported time spent walking and biking was strongly overestimated when compared to GPS measurements. Participants estimated their time spent in motorised transport accurately. Several variables were associated with differences in mobility patterns, we found for instance that obese people (BMI > 30 kg/m(2)) spent less time in non-motorised transport (GMR 0.69-0.74) and people with COPD tended to travel longer distances from home in motorised transport (GMR 1.42-1.51). If time spent walking outdoors and biking is relevant for the exposure to environmental factors, then relying on the home address as a proxy for exposure location may introduce misclassification. In addition, this misclassification is potentially differential, and specific groups of people will show stronger misclassification of exposure than others. Performing GPS measurements and identifying explanatory factors of mobility patterns may assist in regression calibration of self-reports in other studie

Relationship between Coxiella burnetii (Q fever) antibody serology and time spent outdoors

BACKGROUND/AIM: From 2007 through 2010, the Netherlands experienced the largest recorded Q fever outbreak to date. People living closer to Coxiella burnetii infected goat farms were at increased risk for acute Q fever. Time spent outdoors near infected farms may have contributed to exposure to C. burnetii. The aim of this study was to retrospectively evaluate whether hours/week spent outdoors, in the vicinity of previously C. burnetii infected goat farms, was associated with presence of antibodies against C. burnetii in residents of a rural area in the Netherlands. METHODS: Between 2014-2015, we collected C. burnetii antibody serology and self-reported data about habitual hours/week spent outdoors near the home from 2494 adults. From a subgroup we collected 941 GPS tracks, enabling analyses of active mobility in the outbreak region. Participants were categorised as exposed if they spent time within specified distances (500m, 1000m, 2000m, or 4000m) of C. burnetii infected goat farms. We evaluated whether time spent near these farms was associated with positive C. burnetii serology using spline analyses and logistic regression. RESULTS: People that spent more hours/week outdoors near infected farms had a significantly increased risk for positive C. burnetii serology (time spent within 2000m of a C. burnetii abortion-wave positive farm, OR 3.6 (1.2-10.6)), compared to people spending less hours/week outdoors. CONCLUSIONS: Outdoor exposure contributed to the risk of becoming C. burnetii serology positive. These associations were stronger if people spent more time near C. burnetii infected farms. Outdoor exposure should, if feasible, be included in outbreak investigations

MOESM1 of Mobility assessment of a rural population in the Netherlands using GPS measurements

Additional file 1. Supplementary data