Near-Roadway Air Pollution and Coronary Heart Disease: Burden of Disease and Potential Impact of a Greenhouse Gas Reduction Strategy in Southern California

Background: Several studies have estimated the burden of coronary heart disease (CHD) mortality from ambient regional particulate matter ≤ 2.5 μm (PM2.5). The burden of near-roadway air pollution (NRAP) generally has not been examined, despite evidence of a causal link with CHD. Objective: We investigated the CHD burden from NRAP and compared it with the PM2.5 burden in the California South Coast Air Basin for 2008 and under a compact urban growth greenhouse gas reduction scenario for 2035. Methods: We estimated the population attributable fraction and number of CHD events attributable to residential traffic density, proximity to a major road, elemental carbon (EC), and PM2.5 compared with the expected disease burden if the population were exposed to background levels of air pollution. Results: In 2008, an estimated 1,300 CHD deaths (6.8% of the total) were attributable to traffic density, 430 deaths (2.4%) to residential proximity to a major road, and 690 (3.7%) to EC. There were 1,900 deaths (10.4%) attributable to PM2.5. Although reduced exposures in 2035 should result in smaller fractions of CHD attributable to traffic density, EC, and PM2.5, the numbers of estimated deaths attributable to each of these exposures are anticipated to increase to 2,500, 900, and 2,900, respectively, due to population aging. A similar pattern of increasing NRAP-attributable CHD hospitalizations was estimated to occur between 2008 and 2035. Conclusion: These results suggest that a large burden of preventable CHD mortality is attributable to NRAP and is likely to increase even with decreasing exposure by 2035 due to vulnerability of an aging population. Greenhouse gas reduction strategies developed to mitigate climate change offer unexploited opportunities for air pollution health co-benefits

The San Diego 2007 wildfires and Medi-Cal emergency department presentations, inpatient hospitalizations, and outpatient visits: An observational study of smoke exposure periods and a bidirectional case-crossover analysis.

BACKGROUND:The frequency and intensity of wildfires is anticipated to increase as climate change creates longer, warmer, and drier seasons. Particulate matter (PM) from wildfire smoke has been linked to adverse respiratory and possibly cardiovascular outcomes. Children, older adults, and persons with underlying respiratory and cardiovascular conditions are thought to be particularly vulnerable. This study examines the healthcare utilization of Medi-Cal recipients during the fall 2007 San Diego wildfires, which exposed millions of persons to wildfire smoke. METHODS AND FINDINGS:Respiratory and cardiovascular International Classification of Diseases (ICD)-9 codes were identified from Medi-Cal fee-for-service claims for emergency department presentations, inpatient hospitalizations, and outpatient visits. For a respiratory index and a cardiovascular index of key diagnoses and individual diagnoses, we calculated rate ratios (RRs) for the study population and different age groups for 3 consecutive 5-day exposure periods (P1 [October 22-26], P2 [October 27-31], and P3 [November 1-5]) versus pre-fire comparison periods matched on day of week (5-day periods starting 3, 4, 5, 6, 8, and 9 weeks before each exposed period). We used a bidirectional symmetric case-crossover design to examine emergency department presentations with any respiratory diagnosis and asthma specifically, with exposure based on modeled wildfire-derived fine inhalable particles that are 2.5 micrometers and smaller (PM2.5). We used conditional logistic regression to estimate odds ratios (ORs), adjusting for temperature and relative humidity, to assess same-day and moving averages. We also evaluated the United States Environmental Protection Agency (EPA)'s Air Quality Index (AQI) with this conditional logistic regression method. We identified 21,353 inpatient hospitalizations, 25,922 emergency department presentations, and 297,698 outpatient visits between August 16 and December 15, 2007. During P1, total emergency department presentations were no different than the reference periods (1,071 versus 1,062.2; RR 1.01; 95% confidence interval [CI] 0.95-1.08), those for respiratory diagnoses increased by 34% (288 versus 215.3; RR 1.34; 95% CI 1.18-1.52), and those for asthma increased by 112% (58 versus 27.3; RR 2.12; 95% CI 1.57-2.86). Some visit types continued to be elevated in later time frames, e.g., a 72% increase in outpatient visits for acute bronchitis in P2. Among children aged 0-4, emergency department presentations for respiratory diagnoses increased by 70% in P1, and very young children (0-1) experienced a 243% increase for asthma diagnoses. Associated with a 10 μg/m3 increase in PM2.5 (72-hour moving average), we found 1.08 (95% CI 1.04-1.13) times greater odds of an emergency department presentation for asthma. The AQI level "unhealthy for sensitive groups" was associated with significantly elevated odds of an emergency department presentation for respiratory conditions the day following exposure, compared to the AQI level "good" (OR 1.73; 95% CI 1.18-2.53). Study limitations include the use of patient home address to estimate exposures and demographic differences between Medi-Cal beneficiaries and the general population. CONCLUSIONS:Respiratory diagnoses, especially asthma, were elevated during the wildfires in the vulnerable population of Medi-Cal beneficiaries. Wildfire-related healthcare utilization appeared to persist beyond the initial high-exposure period. Increased adverse health events were apparent even at mildly degraded AQI levels. Significant increases in health events, especially for respiratory conditions and among young children, are expected based on projected climate scenarios of wildfire frequency in California and globally

Conditional logistic regression of emergency department presentations for respiratory diagnoses and asthma with wildfire PM_2.5, and ORs adjusted for daily temperature and relative humidity in San Diego County during 2007 wildfires.

<p>Conditional logistic regression of emergency department presentations for respiratory diagnoses and asthma with wildfire PM_2.5, and ORs adjusted for daily temperature and relative humidity in San Diego County during 2007 wildfires.</p

Age, sex, and race/ethnicity of Medi-Cal beneficiaries under age 65 with fee-for-service claims during health data availability period (August 1–December 31, 2007) and peak fire period (October 22–26, 2007) in San Diego County.

<p>Age, sex, and race/ethnicity of Medi-Cal beneficiaries under age 65 with fee-for-service claims during health data availability period (August 1–December 31, 2007) and peak fire period (October 22–26, 2007) in San Diego County.</p

Map of San Diego County wildfire PM_2.5 by zip code, October 22–26, 2007 fire period.

<p>Maps show zip code mean of average daily PM_2.5 values across the 5-day fire-exposure period. Green indicates satisfactory levels according to the US EPA’s 24-hour standard. Fire extent is hatched. PM_2.5, fine inhalable particles that are 2.5 micrometers and smaller; US EPA, US Environmental Protection Agency.</p

Summary of modeled wildfire emissions: mean 24-hour, maximum 24-hour, and percentiles of 24-hour wildfire PM_2.5 concentrations across zip codes and dates during study periods in San Diego County in 2007.

<p>Summary of modeled wildfire emissions: mean 24-hour, maximum 24-hour, and percentiles of 24-hour wildfire PM_2.5 concentrations across zip codes and dates during study periods in San Diego County in 2007.</p

Respiratory and cardiovascular healthcare encounters in San Diego County during 2007 fire period.

<p>RRs for the 5-day periods starting from October 22 and for claims related to emergency department presentations (red, circle), inpatient hospitalizations (green, triangle), and outpatient visits (blue, square). The top row shows encounters for specific respiratory diagnoses. The bottom row shows encounters for the respiratory index, cardiovascular index, and total encounters (all diagnoses). COPD, chronic obstructive pulmonary disease; RR, rate ratio.</p

Respiratory healthcare encounters, age-specific results in San Diego County during 2007 fire period.

<p>RRs by age group (young children aged 0–1, 2–4, 0–4; older children aged 5–17; and adults under age 65) for the 5-day exposure period starting from October 22 for emergency department presentations, inpatient hospitalizations, and outpatient visits. COPD, chronic obstructive pulmonary disease; RR, rate ratio.</p

AQI categories—ORs from conditional logistic regression of respiratory emergency department presentations in San Diego County during 2007 wildfires.

<p>AQI categories—ORs from conditional logistic regression of respiratory emergency department presentations in San Diego County during 2007 wildfires.</p

Wildfire PM_2.5 by day in San Diego County zip codes during 2007 wildfires.

<p>Daily average wildfire PM_2.5 for each of 101 zip codes in San Diego County for a period just prior to the 2007 Firestorm and for the 5-day windows of time following the start of the fires on October 22. The average for all zip codes is shown in blue, and the US EPA 24-hour PM_2.5 standard is in red. PM, particulate matter; PM_2.5, fine inhalable particles that are 2.5 micrometers and smaller; US EPA, Environmental Protection Agency.</p