Kathleen M. Mortimer

The effect of air pollution on inner-city children with asthma

The effect of daily ambient air pollution was examined within a cohort of 846 asthmatic children residing in eight urban areas of the USA, using data from the National Cooperative Inner-City Asthma Study. Daily air pollution concentrations were extracted from the Aerometric Information Retrieval System database from the Environment Protection Agency in the USA. Mixed linear models and generalized estimating equation models were used to evaluate the effects of several air pollutants (ozone, sulphur dioxide (SO2), nitrogen dioxide (NO2) and particles with a 50% cut-off aerodynamic diameter of 10 µm (PM10) on peak expiratory flow rate (PEFR) and symptoms in 846 children with a history of asthma (ages 4–9 yrs). None of the pollutants were associated with evening PEFR or symptom reports. Only ozone was associated with declines in morning % PEFR (0.59% decline (95% confidence interval (CI) 0.13–1.05%) per interquartile range (IQR) increase in 5‐day average ozone). In single pollutant models, each pollutant was associated with an increased incidence of morning symptoms: (odds ratio (OR)=1.16 (95% CI 1.02–1.30) per IQR increase in 4‐day average ozone, OR=1.32 (95% CI 1.03–1.70) per IQR increase in 2‐day average SO2, OR=1.48 (95% CI 1.02–2.16) per IQR increase in 6‐day average NO2 and OR=1.26 (95% CI 1.0–1.59) per IQR increase in 2‐day average PM10. This longitudinal analysis supports previous time-series findings that at levels below current USA air-quality standards, summer-air pollution is significantly related to symptoms and decreased pulmonary function among children with asthma.

Implementation of G-Computation on a Simulated Data Set: Demonstration of a Causal Inference Technique

The growing body of work in the epidemiology literature focused on G-computation includes theoretical explanations of the method but very few simulations or examples of application. The small number of G-computation analyses in the epidemiology literature relative to other causal inference approaches may be partially due to a lack of didactic explanations of the method targeted toward an epidemiology audience. The authors provide a step-by-step demonstration of G-computation that is intended to familiarize the reader with this procedure. The authors simulate a data set and then demonstrate both G-computation and traditional regression to draw connections and illustrate contrasts between their implementation and interpretation relative to the truth of the simulation protocol. A marginal structural model is used for effect estimation in the G-computation example. The authors conclude by answering a series of questions to emphasize the key characteristics of causal inference techniques and the G-computation procedure in particular.

Successful Techniques for Retention of Study Participants in an Inner-City Population

The purpose of this work was to describe methods of retaining participants in studies of inner-city populations, including the timing and intensity of contacts; and to describe the characteristics of participants who did not complete all follow-up interviews and/or return all peak flow diaries in the National Cooperative Inner-City Asthma Study. A cohort study design was used involving hospital emergency rooms and community clinics in seven major urban areas. Participants included 1337 4- to 9-year-old asthmatic children and their caretakers. Nearly 89% of participants completed 3-, 6-, and 9-month follow-up interviews. The 15% of participants who completed a baseline interview on the weekends were significantly more likely to complete follow-up interviews on a weekend. The percent of follow-up interviews conducted in person increased over time from 5% to 8%. The percent of participants with complete follow-up increased as the number of contact names increased (86% with zero contacts, 91% with two contracts; p = 0.03, test for trend). Participants who required at least four phone calls to complete the 3- and 6-month assessment were significantly more likely to be black, have higher participant stress, and have a smoker in the household (p < 0.05). Multiple logistic regression suggests that higher social support and lower parental stress were both predictors of completed interviews. Within our study sample of inner-city minority participants with asthmatic children, only a small proportion of participants missed any follow-up interviews. Increased caretaker stress, decreased social support, and inability to provide several alternate contacts were all predictive of retention problems. Having a flexible staff, computer tracking, and face-to-face recruitment appear essential to achieving nearly complete follow-up within a population historically difficult to follow.

Short-Term Effects of Air Pollution on Wheeze in Asthmatic Children in Fresno, California

Background Although studies have demonstrated that air pollution is associated with exacerbation of asthma symptoms in children with asthma, little is known about the susceptibility of subgroups, particularly those with atopy. Objective This study was designed to evaluate our a priori hypothesis that identifiable subgroups of asthmatic children are more likely to wheeze with exposure to ambient air pollution. Methods A cohort of 315 children with asthma, 6–11 years of age, was recruited for longitudinal follow-up in Fresno, California (USA). During the baseline visit, children were administered a respiratory symptom questionnaire and allergen skin-prick test. Three times a year, participants completed 14-day panels during which they answered symptom questions twice daily. Ambient air quality data from a central monitoring station were used to assign exposures to the following pollutants: particulate matter ≤ 2.5 μm in aerodynamic diameter, particulate matter between 2.5 and 10 μm in aerodynamic diameter (PM10–2.5), elemental carbon, nitrogen dioxide (NO2), nitrate, and O3. Results For the group as a whole, wheeze was significantly associated with short-term exposures to NO2 [odds ratio (OR) = 1.10 for 8.7-ppb increase; 95% confidence interval (CI), 1.02–1.20] and PM10–2.5 (OR = 1.11 for 14.7-μg/m3 increase; 95% CI, 1.01–1.22). The association with wheeze was stronger for these two pollutants in children who were skin-test positive to cat or common fungi and in boys with mild intermittent asthma. Conclusion A pollutant associated with traffic emissions, NO2, and a pollutant with bioactive constituents, PM10–2.5, were associated with increased risk of wheeze in asthmatic children living in Fresno, California. Children with atopy to cat or common fungi and boys with mild intermittent asthma were the subgroups for which we observed the largest associations.

Air pollution and pulmonary function in asthmatic children: effects of prenatal and lifetime exposures.

Background: Prenatal and early life periods represent critical windows for oxidant pollutant-induced lung remodeling. The objective of this study was to examine the association of prenatal and lifetime exposures to air pollutants with pulmonary function in a cohort of children with asthma. Methods: Prenatal and lifetime exposure to several air pollutants was reconstructed for 232 children with asthma from the San Joaquin Valley of California, USA. Prenatal and lifetime residences were geocoded. We obtained data on monthly average ozone (O3), carbon monoxide (CO), nitrogen dioxide (NO2), and particulate matter with a median aerodynamic diameter <10 μm (PM10) concentrations. Metrics were created for key developmental periods. Predictive models were developed for 8 pulmonary function measures. A newly-developed stepwise model selection procedure—the Deletion/Substitution/Addition algorithm—was implemented and results were compared with those obtained using traditional stepwise methods. Results: Second-trimester exposure to NO2 negatively affected forced vital capacity (FVC) and forced expiratory volume in 1 second (FEV1), and first trimester exposure to PM10 negatively affected peak expiratory flow (PEF) rate. Exposure to CO in early years of life also had a negative effect on FEV1/FVC and forced expiratory flow between 25% and 75% of FVC (FEF25–75)/FVC. Second trimester exposure to PM10 and exposure to CO in the first 6 years of life had negative effects on forced expiratory flow at 25% of FVC. Prenatal, but not trimester-specific, exposure to CO was negatively associated with FEF25–75. Effects were limited to subgroups, such as children who were African American, those diagnosed with asthma before the age of 2 years, and those exposed to maternal smoking during pregnancy. Conclusion: Prenatal and early-life exposures to CO, PM10, and NO2 have a negative effect on pulmonary function in subgroups of asthmatic children.

Pediatric Asthma Care in the Emergency Department: Measuring the Quality of History-Taking and Discharge Planning

The National Asthma Education and Prevention Program NAEPP Guidelines include recommendations for history-taking and discharge planning during an asthma visit, but there are no tools to measure performance. The objectives of this study were to define and operationalize key elements of history-taking and discharge planning, to develop a tool for measuring these elements, and to evaluate the quality of history-taking and discharge planning in the emergency department (ED) during visits for asthma using the new tool. Expert opinion and extensive literature review were used to develop a 13-item checklist containing items that should be documented during history-taking and provided during discharge planning for an ED visit for an acute asthma exacerbation by children. A convenience sample of 90 pediatric emergency medicine physicians and allergists rated each item in the checklist. The checklist was used to score audiotapes of asthma visits in the ED. Subjects were 154 parents of asthmatic children aged 4-9 years seeking care in nine inner-city EDs affiliated with asthma centers participating in the National Cooperative Inner-City Asthma Study and the physician/providers who delivered care. Seven of the 13 items on the checklist were rated as required to be performed by more than 90% of the allergist/pediatric emergency medicine physicians. Only 10% of the 154 visits included all seven of the highly rated items, whereas 19% of the visits included three or fewer. Only 7 of the 13 items (54%) were performed in more than 50% of the visits, and 4 items were performed in fewer than 25% of visits. Based on expert ratings, the checklist for measuring elements of history-taking and discharge planning during asthma visits appears to have considerable face validity. In the visits studied, the overall performance of these elements was low. Interventions to improve performance on the checklist might lead to improved care for children with asthma who frequent the ED.

School-based asthma surveillance: A comparison of student and parental report

This study addressed the comparability of data obtained from a student‐based and parent‐based asthma and respiratory health survey. Our goal was to ascertain whether there were meaningful and systematic differences in asthma classification based on symptom and diagnosis reports obtained separately from students and their parents. A brief, written survey, based on the International Study of Asthma and Allergy in Children questionnaire, was administered to 6th through 10th grade students in two schools in Oakland, CA, USA. Students who reported asthma‐like indicators for the previous 12‐month period were defined as positive and a more extensive questionnaire was mailed home to those parents. A more refined classification of asthma based on parent report of indicators was compared with student report. Forty‐four percent of 1298 students were classified as positive for current asthma‐like symptoms and 50% of parent surveys were returned. For the positive students with parent surveys, 59% were classified as ‘probable’ for asthma based on the parent survey. Overall, the agreement between parent and students’ classification was 70%, and 83% for students with a parent report of physician diagnosis of asthma. Students who were discordant with parents for physician diagnosis of asthma were more likely to be male, and more likely to have a parent report of unscheduled Emergency Department visit for wheezing or trouble breathing. Findings indicated that with the exception of medication, students reported asthma indicators more frequently that parents, independent of classification. Student report of physician diagnosis with a 12‐month report of an asthma symptom was determined to be a good indicator of probable current asthma. Inclusion of or reliance on a parental questionnaire is not likely to improve the reliability of a school‐based asthma surveillance program in our population.

Early-lifetime exposure to air pollution and allergic sensitization in children with asthma.

Observations on the association between exposure to common outdoor air pollutants and allergic sensitization have not been consistent. Little research has been done on the effects of prenatal exposure or the effect among asthmatics. The association between prenatal and early-life exposures and outdoor air pollutants with allergic sensitization was examined within a cohort of 170 children ages 6–11 years with asthma, living in the Central Valley of California. Allergic sensitization was ascertained by skin-prick tests to 14 allergens. Prenatal and early-life exposure to ozone (O3), nitrogen dioxide (NO2), carbon monoxide (CO) and particulate matter with a median aerodynamic diameter < 10 μ m (PM10) was reconstructed for each child. Models were developed for sensitized to (a) any allergen, (b) at least one outdoor allergen, and (c) at least one indoor allergen. In multivariable analyses, higher exposure to CO during pregnancy was associated with an increased risk of sensitization to at least one outdoor allergen. The largest effect was seen for the association between exposure to 8-hour daily maximum CO during pregnancy and sensitization to at least one outdoor allergen. (OR = 1.55 (95% CI: 1.01, 2.37)) per interquartile range (IQR) increase.) Similar effects estimates were seen for 2nd trimester exposure to CO, but these were less precisely estimated (OR = 1.45 (95%CI: 0.90, 2.35)). No significant associations with the pollutants were seen for sensitization to allergens in general or to at least one indoor allergen. Exposure to traffic-related pollutants during pregnancy may increase the risk of sensitization to outdoor allergens among asthmatic children.

Altered pulmonary function in children with asthma associated with highway traffic near residence.

Cross-sectional analyses were conducted to evaluate the effects of exposure to highway traffic on pulmonary function in Fresno, California. Traffic and spirometry data were available for 214 children (enrollment ages six to 11 years). Multiple linear regression was used to evaluate the relations between pulmonary function and traffic parameters. Heavy-duty vehicle count was used as a surrogate measure for diesel-related exposures. Pulmonary function was non-significantly associated with longer distance-to-road and non-significantly associated with higher traffic intensity. Evaluation of effect modification by FEF25–75/FVC (a measure of intrinsic airway size) showed that all pulmonary function measures of flow were significantly inversely related to a traffic metric that incorporates traffic intensity and roadway proximity. The results indicate that residence proximity to highway traffic is associated with lower pulmonary function among children with asthma, and smaller airway size is an important modifier of the effect of traffic exposure on pulmonary function and a marker of increased susceptibility.

Exposure to Traffic-related Air Pollution During Pregnancy and Term Low Birth Weight: Estimation of Causal Associations in a Semiparametric Model

Traffic-related air pollution is recognized as an important contributor to health problems. Epidemiologic analyses suggest that prenatal exposure to traffic-related air pollutants may be associated with adverse birth outcomes; however, there is insufficient evidence to conclude that the relation is causal. The Study of Air Pollution, Genetics and Early Life Events comprises all births to women living in 4 counties in Californias San Joaquin Valley during the years 2000-2006. The probability of low birth weight among full-term infants in the population was estimated using machine learning and targeted maximum likelihood estimation for each quartile of traffic exposure during pregnancy. If everyone lived near high-volume freeways (approximated as the fourth quartile of traffic density), the estimated probability of term low birth weight would be 2.27% (95% confidence interval: 2.16, 2.38) as compared with 2.02% (95% confidence interval: 1.90, 2.12) if everyone lived near smaller local roads (first quartile of traffic density). Assessment of potentially causal associations, in the absence of arbitrary model assumptions applied to the data, should result in relatively unbiased estimates. The current results support findings from previous studies that prenatal exposure to traffic-related air pollution may adversely affect birth weight among full-term infants.