Brian Malig

The effects of fine particle components on respiratory hospital admissions in children.

Background Epidemiologic studies have demonstrated an association between acute exposure to ambient fine particles and both mortality and morbidity. Less is known about the relative impacts of the specific chemical constituents of particulate matter < 2.5 μm in aerodynamic diameter (PM2.5) on hospital admissions. Objective This study was designed to estimate the risks of exposure to PM2.5 and several species on hospital admissions for respiratory diseases among children. Data and Methods We obtained data on daily counts of hospitalizations for children < 19 and < 5 years of age for total respiratory diseases and several subcategories including pneumonia, acute bronchitis, and asthma for six California counties from 2000 through 2003, as well as ambient concentrations of PM2.5 and its constituents, including elemental carbon (EC), organic carbon (OC), and nitrates (NO3). We used Poisson regression to estimate risks while controlling for important covariates. Results We observed associations between several components of PM2.5 and hospitalization for all of the respiratory outcomes examined. For example, for total respiratory admissions for children < 19 years of age, the interquartile range for a 3-day lag of PM2.5, EC, OC, NO3, and sulfates was associated with an excess risk of 4.1% [95% confidence interval (CI), 1.8–6.4], 5.4% (95% CI, 0.8–10.3), 3.4% (95% CI, 1.1–5.7), 3.3% (95% CI, 1.1–5.5), and 3.0% (95% CI, 0.4–5.7), respectively. We also observed associations for several metals. Additional associations with several of the species, including potassium, were observed in the cool season. Conclusion Components of PM2.5 were associated with hospitalization for several childhood respiratory diseases including pneumonia, bronchitis, and asthma. Because exposure to components (e.g., EC, OC, NO3, and K) and their related sources, including diesel and gasoline exhaust, wood smoke, and other combustion sources, are ubiquitous in the urban environment, it likely represents an identifiable and preventable risk factor for hospitalization for children.

The Effects of Temperature and Use of Air Conditioning on Hospitalizations

Several investigators have documented the effect of temperature on mortality, although fewer have studied its impact on morbidity. In addition, little is known about the effectiveness of mitigation strategies such as use of air conditioners (ACs). The authors investigated the association between temperature and hospital admissions in California from 1999 to 2005. They also determined whether AC ownership and usage, assessed at the zip-code level, mitigated this association. Because of the unique spatial pattern of income and climate in California, confounding of AC effects by other local factors is less likely. The authors included only persons who had a temperature monitor within 25 km of their residential zip code. Using a time-stratified case-crossover approach, the authors observed a significantly increased risk of hospitalization for multiple diseases, including cardiovascular disease, ischemic heart disease, ischemic stroke, respiratory disease, pneumonia, dehydration, heat stroke, diabetes, and acute renal failure, with a 10°F increase in same-day apparent temperature. They also found that ownership and usage of ACs significantly reduced the effects of temperature on these health outcomes, after controlling for potential confounding by family income and other socioeconomic factors. These results demonstrate important effects of temperature on public health and the potential for mitigation.

The impact of components of fine particulate matter on cardiovascular mortality in susceptible subpopulations

Background: Several studies have demonstrated associations between daily mortality and ambient particulate matter less than 2.5 microns in diameter (fine particles or PM2.5). Few, however, have examined the relative toxicities of PM2.5 constituents, including elemental carbon and organic carbon (EC and OC, respectively), nitrates and transition metals. There is also little information about whether associations between PM2.5 constituents and mortality are modified by socioeconomic and demographic factors. Aim: To examine associations of daily cardiovascular mortality with PM2.5 and its constituents after stratification by gender, race/ethnicity and education, using data from six California counties during 2000 to 2003. Methods: The association of daily counts of cardiovascular mortality with PM2.5 components was analysed using time-series regression analyses. Poisson models with natural splines were used to control for time-varying covariates such as season and weather. Separate models were run after stratification by gender, race/ethnicity (White, Hispanic, Black) and education (high school graduation or not). Models were run for each county and results were combined using random effects meta-analysis. Results: Daily counts of cardiovascular mortality were associated with PM2.5 and several of its species including EC, OC, nitrates, sulphates, potassium, copper and iron. For many of these species, there were significantly higher effect estimates among those with lower educational attainment and Hispanic individuals. For example, while essentially no association was observed for individuals who graduated from high school, an interquartile change in several of the components of PM2.5 was associated with a 3–5% increase in daily mortality among non-high school graduates. Conclusion: There is evidence that several PM2.5 constituents may represent important contributors to cardiovascular mortality. Many of these constituents are generated by motor vehicles, especially those with diesel engines, and by residential wood combustion. In addition, factors associated with low educational attainment may increase susceptibility to PM2.5 and its components.

Residential Traffic and Children's Respiratory Health

Background Living near traffic has been associated with asthma and other respiratory symptoms. Most studies, however, have been conducted in areas with high background levels of ambient air pollution, making it challenging to isolate an independent effect of traffic. Additionally, most investigations have used surrogates of exposure, and few have measured traffic pollutants directly as part of the study. Objective We conducted a cross-sectional study of current asthma and other respiratory symptoms in children (n = 1,080) living at varying distances from high-traffic roads in the San Francisco Bay Area, California, a highly urbanized region characterized by good regional air quality due to coastal breezes. Methods We obtained health information and home environmental factors by parental questionnaire. We assessed exposure with several measures of residential proximity to traffic calculated using geographic information systems, including traffic within a given radius and distance to major roads. We also measured traffic-related pollutants (nitrogen oxides and nitrogen dioxide) for a subset of households to determine how well traffic metrics correlated with measured traffic pollutants. Results Using multivariate logistic regression analyses, we found associations between current asthma and residential proximity to traffic. For several traffic metrics, children whose residences were in the highest quintile of exposure had approximately twice the adjusted odds of current asthma (i.e., asthma episode in the preceeding 12 months) compared with children whose residences were within the lowest quintile. The highest risks were among those living within 75 m of a freeway/highway. Most traffic metrics correlated moderately well with actual pollutant measurements. Conclusion Our findings provide evidence that even in an area with good regional air quality, proximity to traffic is associated with adverse respiratory health effects in children.

The effect of high ambient temperature on emergency room visits.

Background: The association between temperature and mortality has been widely researched, although the association between temperature and morbidity has been less studied. We examined the association between mean daily apparent temperature and emergency room (ER) visits in California. Methods: We used a time-stratified case-crossover design, restricting our data to the warm seasons of 2005–2008 in 16 climate zones. The study population included cases residing within 10 km of meteorologic monitors. Conditional logistic regression models with apparent temperature were applied by climate zone; these models were then combined in meta-analyses to estimate overall effects. Our analyses considered the effects by disease subgroup, race/ethnic group, age group, and potential confounding by air pollutants. Results: More than 1.2 million ER visits were included. Positive associations were found for same-day apparent temperature and ischemic heart disease (% excess risk per 10°F = 1.7 [95% confidence interval = 0.2 to 3.3]), ischemic stroke (2.8 [0.9 to 4.7]), cardiac dysrhythmia (2.8 [0.9 to 4.9]), hypotension (12.7 [8.3 to 17.4]), diabetes (4.3 [2.8 to 5.9]), intestinal infection (6.1 [3.3 to 9.0]), dehydration (25.6 [21.9 to 29.4]), acute renal failure (15.9 [12.7 to 19.3]), and heat illness (393.3 [331.2 to 464.5]). Negative associations were found for aneurysm, hemorrhagic stroke, and hypertension. Most of these estimates remained relatively unchanged after adjusting for air pollutants. Risks often varied by age or racial/ethnic group. Conclusions: Increased temperatures were found to have same-day effects on ER admission for several outcomes. Age and race/ethnicity seemed to modify some of these impacts.

High ambient temperature and mortality in California: exploring the roles of age, disease, and mortality displacement.

Investigators have consistently demonstrated associations between elevated temperatures and mortality worldwide. Few have recently focused on identifying vulnerable subgroups, and far fewer have determined whether at least some of the observed effect may be a manifestation of mortality displacement. We examined mean daily apparent temperature and mortality in 13 counties in California during the warm season from 1999 to 2006 to identify age and disease subgroups that are at increased risk, and to evaluate the potential effect of mortality displacement. The time-series method using the Poisson regression was applied for data analysis for single lag days of 0-20 days, and for cumulative average lag days of five and ten days. Significant associations were observed for the same-day (excess risk=4.3% per 5.6 °C increase in apparent temperature, 95% confidence interval: 3.4, 5.2) continuing up to a maximum of three days following apparent temperature exposure for non-accidental mortality. Similar risks were found for mortality from cardiovascular diseases, respiratory diseases, and among children zero to 18 years of age, and adults and the elderly 50 years and older. Since no significant negative effects were observed in the following single or cumulative days, evidence of mortality displacement was not found. Thus, the effect of temperature on mortality appears to be an event that occurs within three days following exposure, and requires immediate attention for prevention.

Coarse particles and mortality: evidence from a multi-city study in California

Objective: To examine the risk of all-cause and cardiovascular mortality associated with short-term coarse particle exposure in California while addressing issues of exposure misclassification by limiting the study to those residing near a pollution monitor. Methods: Deaths in 15 California counties from 1999 to 2005 were linked to coarse particulate monitoring data. Case deaths were limited to those residing in a zip code within 20 km of a pollution monitor. We used conditional logistic regression with a case-crossover design to estimate county-specific effects of coarse particles. County estimates were then pooled using random-effects meta-analysis to create overall study estimates. Effects specific to race and educational status were also analysed. Results: We observed an increased excess risk (ER) of both all-cause mortality (ER per 10 μg/m3  = 0.7%, 95% CI −0.1 to 1.5) and cardiovascular mortality (ER per 10 μg/m3  = 1.3%, 95% CI 0.1 to 2.5) from a 2-day lag in coarse particles. Greater effects were observed among Hispanics and non-high school graduates. Adjustment for fine particles and decreasing the inclusion buffer to 10 km did not substantively alter the results. Conclusions: Our study provides further evidence of an association between acute exposure to coarse particles and mortality, and supports the hypothesis that lower socioeconomic status groups may be more susceptible to its effects.

Effects of fine particulate matter and its constituents on low birth weight among full-term infants in California.

Relationships between prenatal exposure to fine particles (PM2.5) and birth weight have been observed previously. Few studies have investigated specific constituents of PM2.5, which may identify sources and major contributors of risk. We examined the effects of trimester and full gestational prenatal exposures to PM2.5 mass and 23 PM2.5 constituents on birth weight among 646,296 term births in California between 2000 and 2006. We used linear and logistic regression models to assess associations between exposures and birth weight and risk of low birth weight (LBW; <2500g), respectively. Models were adjusted for individual demographic characteristics, apparent temperature, month and year of birth, region, and socioeconomic indicators. Higher full gestational exposures to PM2.5 mass and several PM2.5 constituents were significantly associated with reductions in term birth weight. The largest reductions in birth weight were associated with exposure to vanadium, sulfur, sulfate, iron, elemental carbon, titanium, manganese, bromine, ammonium, zinc, and copper. Several of these PM2.5 constituents were associated with increased risk of term LBW. Reductions in birth weight were generally larger among younger mothers and varied by race/ethnicity. Exposure to specific constituents of PM2.5, especially traffic-related particles, sulfur constituents, and metals, were associated with decreased birth weight in California.

Chronic PM2.5 exposure and inflammation: determining sensitive subgroups in mid-life women.

BACKGROUND Several cohort studies report associations between chronic exposure to ambient fine particles (PM2.5) and cardiovascular mortality. Uncertainty exists about biological mechanisms responsible for this observation, but systemic inflammation has been postulated. In addition, the subgroups susceptible to inflammation have not been fully elucidated. METHODS We investigated whether certain subgroups are susceptible to the effects of long-term exposure to PM2.5 on C-reactive protein (CRP), a marker of inflammation directly linked to subsequent cardiovascular disease. We used data from the SWAN cohort of 1923 mid-life women with up to five annual repeated measures of CRP. Linear mixed and GEE models accounting for repeated measurements within an individual were used to estimate the effects of prior-year PM2.5 exposure on CRP. We examined CRP as a continuous and as binary outcome for CRP greater than 3mg/l, a level of clinical significance. RESULTS We found strong associations between PM2.5 and CRP among several subgroups. For example a 10 µg/m(3) increase in annual PM2.5 more than doubled the risk of CRP greater than 3mg/l in older diabetics, smokers and the unmarried. Larger effects were also observed among those with low income, high blood pressure, or who were using hormone therapy, with indications of a protective effects for those using statins or consuming moderate amounts of alcohol. CONCLUSIONS In this study, we observed significant associations between long-term exposure to PM2.5 and CRP in several susceptible subgroups. This suggests a plausible pathway by which exposure to particulate matter may be associated with increased risk of cardiovascular disease.

Coarse Particles and Respiratory Emergency Department Visits in California

Although respiratory disease has been strongly connected to fine particulate air pollution (particulate matter <2.5 μm in diameter (PM2.5)), evidence has been mixed regarding the effects of coarse particles (particulate matter from 2.5 to 10 μm in diameter), possibly because of the greater spatial heterogeneity of coarse particles. In this study, we evaluated the relationship between coarse particles and respiratory emergency department visits, including common subdiagnoses, from 2005 to 2008 in 35 California counties. A time-stratified case-crossover design was used to help control for time-invariant confounders and seasonal influences, and the study population was limited to those residing within 20 km of pollution monitors to mitigate the influence of spatial heterogeneity. Significant associations between respiratory emergency department visits and coarse particle levels were observed. Asthma visits showed associations (for 2-day lag, excess risk per 10 μg/m³ = 3.3%, 95% confidence interval: 2.0, 4.6) that were robust to adjustment by other common air pollutants (particles <2.5 μm in diameter, ozone, nitrogen dioxide, carbon monoxide, and sulfur dioxide). Pneumonia and acute respiratory infection visits were not associated, although some suggestion of a relationship with chronic obstructive pulmonary disease visits was present. Our results indicate that coarse particle exposure may trigger asthma exacerbations requiring emergency care, and reducing exposures among asthmatic persons may provide benefits.