Exposure Assessment in Cohort Studies of Childhood Asthma

Abstract

BackgroundThe environment is suspected to play an important role in the development of childhood asthma. Cohort studies are a powerful observational design for studying exposure–response relationships, but their power depends in part upon the accuracy of the exposure assessment.ObjectiveThe purpose of this paper is to summarize and discuss issues that make accurate exposure assessment a challenge and to suggest strategies for improving exposure assessment in longitudinal cohort studies of childhood asthma and allergies.Data synthesisExposures of interest need to be prioritized, because a single study cannot measure all potentially relevant exposures. Hypotheses need to be based on proposed mechanisms, critical time windows for effects, prior knowledge of physical, physiologic, and immunologic development, as well as genetic pathways potentially influenced by the exposures. Modifiable exposures are most important from the public health perspective. Given the interest in evaluating gene–environment interactions, large cohort sizes are required, and planning for data pooling across independent studies is critical. Collection of additional samples, possibly through subject participation, will permit secondary analyses. Models combining air quality, environmental, and dose data provide exposure estimates across large cohorts but can still be improved.ConclusionsExposure is best characterized through a combination of information sources. Improving exposure assessment is critical for reducing measurement error and increasing power, which increase confidence in characterization of children at risk, leading to improved health outcomes.

Gut microbiota of healthy Canadian infants: profiles by mode of delivery and infant diet at 4 months

“…Overall, the mean rarefied Chao1 score for species richness was 12.0 (range [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. The mean Shannon diversity index was 1.38, ranging from 0.17 to 2.36 (Table 4).…”

“…19 Thus, the gut microbiota is essential to human health, yet the acquisition and development of this microbial community during infancy remains poorly understood. 3 In the current study, we address this gap in knowledge using new sequencing technology and detailed exposure assessments 20 of healthy Can adian infants selected from a national birth cohort to provide representative, comprehensive profiles of gut microbiota according to mode of delivery and infant diet. 21 We used quantitative polymerase chain reaction as described by Penders and colleagues 5 for targeted analysis of Clostridium difficile because of the organism's association with atopic allergic disease in a previous study.…”

Improved exposure characterization with robotic (PIPER) sampling and association with children’s respiratory symptoms, asthma and eczema

“…An accurate method for estimating environmental exposure to airborne contaminants is essential to understanding both the environment and possible links to respiratory health problems. Until now characterizing children's exposures has relied primarily on measurements of settled dust or general area stationary indoor monitors (SIM) [2]. While some studies have found a significant association between concentrations of indoor particulate matter (PM) and respiratory morbidity, others have not [3-7].…”

Effects of long-term exposure to PM10and NO2on asthma and wheeze in a prospective birth cohort

“…Recent reviews have highlighted the need for improved exposure assessment methods in epidemiological studies 5 12. Although ideally one would monitor personal exposure throughout life, this is clearly not feasible and alternative methods of assigning an index of exposure have been used, for example, central outdoor monitors, land use regression (LUR) models or temporary indoor static monitors.…”