Rupa Basu

Characterizing temperature and mortality in nine California counties.

Background: Elevated temperature has been associated with increased mortality. Few epidemiologic studies, however, have considered air pollutants as potential confounders or effect modifiers. None has focused on California, where the climate is generally mild and pollution levels tend to be high—an ideal setting to examine the independent effect of temperature from air pollution. Methods: We examined the association between mean daily apparent temperature and nonaccidental mortality in 9 counties throughout California from May to September 1999–2003. Data were obtained from the National Climatic Data Center (temperature and relative humidity), the California Department of Health Services (mortality), and the California Air Resources Board (particulate matter, ozone, carbon monoxide, and nitrogen dioxide). We conducted a time-stratified case-crossover study, with a time-series analysis as a sensitivity analysis, adjusting for day of the week using both methods and adjusting for time trend in the time-series analysis. We first obtained county-specific estimates and then combined them using meta-analytic methods. Results: A total of 248,019 deaths were included. Each 10° (Fahrenheit) increase in same-day mean apparent temperature corresponded to a 2.3% increase in mortality (95% confidence interval = 1.0%–3.6%) in the case-crossover analysis for all 9 counties combined, with nearly identical results produced from the time-series analysis. No air pollutant examined was found to be a significant confounder or effect modifier. Conclusions: Even without extremes in apparent temperature, we observed an association between temperature and mortality in California that was independent of air pollution.

Temperature and Mortality Among the Elderly in the United States: A Comparison of Epidemiologic Methods

Background: Time-series analyses have been used for decades to investigate time-varying environmental exposures. Recently, the case-crossover design has been applied to assess acute effects of air pollution. Our objective was to compare time-series and case-crossover analyses using varying referent periods (ie, unidirectional, ambidirectional, and time-stratified). Methods: We examined the association between temperature and cardiorespiratory mortality among the elderly population in the 20 largest metropolitan areas of the United States. Risks were estimated by season and geographic region in 1992. We obtained weather data from the National Climatic Data Center and mortality data from the Division of Vital Statistics. Conditional logistic regression (case-crossover) and Poisson regression (time-series) were used to estimate the increased risk of cardiorespiratory mortality associated with a 10°F increase in daily temperature, accounting for dew-point temperature and other potential confounding factors. Results: In the time-stratified case-crossover analysis, the strongest associations were found in the summer; in the Southwest, Southeast, Northwest, Northeast, and Midwest, the odds ratios were 1.15 (95% confidence interval = 1.07–1.24), 1.10 (0.96–1.27), 1.08 (0.92–1.26), 1.08 (1.02–1.15), and 1.01 (0.92–1.11), respectively. Mostly null or negative associations were found in the winter, spring, and fall. The ambidirectional case-crossover and the time-series analyses produced quantitatively similar results to those from the time-stratified analysis. The unidirectional analysis produced conflicting results. Conclusions: Inferences from studies of weather and mortality using the ambidirectional or time-stratified case-crossover ap-proaches and the time-series analyses are comparable and provide consistent findings in this study.

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.

ESTIMATING THE MORTALITY EFFECT OF THE JULY 2006 CALIFORNIA HEAT WAVE

OBJECTIVE As a result of the California heat wave in July 2006, county coroners reported that the high temperatures during that period caused approximately 147 deaths. However, heat wave-related deaths are likely to be underreported due to a lack of a clear case definition and the multi-factorial nature of heat-related mortality. Public health policy suggests a need for a careful assessment of mortality following a heat wave. In addition, it is useful to provide a comparison of the mortality impact per degree change during heat waves versus high temperatures observed during non-heat wave periods. DESIGN Daily data were collected for mortality, weather and ozone in seven California counties impacted by the July 2006 heat wave. The association between apparent temperature and daily mortality was assessed using a Poisson regression model and combined across counties in a meta-analysis. These results were then used to estimate the increases in the number of deaths during the heat wave. RESULTS Our analysis indicated that during the July heat wave, there was a 9% (95% CI = 1.6, 16.3) increase in daily mortality per 10 degrees Fahrenheit (F) change in apparent temperature for all counties combined. This estimate is almost 3 times larger than the effect estimated for the full warm season of May-September, during the non-heat wave years. Our estimates also determined that actual mortality during the July 2006 heat wave was 2-3 times greater than the coroner estimates. CONCLUSION This multi-county analysis provides additional evidence that the attributable risk of mortality following a heat wave may be underestimated by examining only direct heat-related deaths. In addition, we have found that the mortality effect per degrees F is several times higher than that reported during non-heat wave periods.

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.

The Impact of Recent Heat Waves on Human Health in California

AbstractThis study examines the health impacts of recent heat waves statewide and for six subregions of California: the north and south coasts, the Central Valley, the Mojave Desert, southern deserts, and northern forests. By using canonical correlation analysis applied to daily maximum temperatures and morbidity data in the form of unscheduled hospitalizations from 1999 to 2009, 19 heat waves spanning 3–15 days in duration that had a significant impact on health were identified. On average, hospital admissions were found to increase by 7% on the peak heat-wave day, with a significant impact seen for several disease categories, including cardiovascular disease, respiratory disease, dehydration, acute renal failure, heat illness, and mental health. Statewide, there were 11 000 excess hospitalizations that were due to extreme heat over the period, yet the majority of impactful events were not accompanied by a heat advisory or warning from the National Weather Service. On a regional basis, the strongest heal...

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.