Skip to main content
eScholarship
Open Access Publications from the University of California

Scholarly Works (9 results)

  • Thesis
  • Peer Reviewed
UC San Diego Electronic Theses and Dissertations (2023)

Background: While the detrimental health effects of extreme heat and wildfire smoke are well established in high-income countries, there is substantially less evidence in low and middle-income settings. This dissertation research aimed to quantify the effects of extreme heat and wildfire smoke through a social vulnerability approach, using the San Diego-Tijuana border as a context to study differential impacts.Methods: This dissertation includes three studies examining the differential impacts of extreme heat and wildfire smoke in a binational context. The first study evaluates the spatial variation in the effect of extreme heat across municipalities in Mexico using a within-community-matched design with a Bayesian Hierarchical model extension and meta-regression to explore socioeconomic drivers. In the second study, we used the San Diego-Tijuana region as a unique context to study the differential effects of wildfire smoke on cardio-respiratory hospitalizations across the border using synthetic control methods (SCM). The third study also used SCM to explore the potential role of wildfire smoke in driving COVID-19 mortality in the San Diego-Tijuana border region. Results: In the first study, we found substantial spatial heterogeneity in the effects of heat across Mexico at the municipality level, and disadvantaged social conditions such as low education, poor housing conditions, and higher marginalization were important predictors of these differences. In the second study, wildfire smoke increased cardio-respiratory hospitalizations in the San Diego-Tijuana border region, with a higher, albeit imprecise, relative change in Tijuana likely driven by a higher poverty rate and increased social vulnerability. Lastly, in the third study, no strong effect of wildfire smoke on COVID-19 mortality was observed in either San Diego or Tijuana. Conclusion: The results of this dissertation indicate that social vulnerability is an important factor in understanding the health risks of extreme heat and wildfire smoke. We hope that highlighting the differential susceptibility of populations to these effects can help inform binational efforts to protect those that are most vulnerable to extreme weather events which will be increasingly prevalent and severe in the context of climate change.

    Cover page: Climate knows no borders: Assessing the role of extreme weather events in driving adverse health outcomes in a binational United States-Mexico border region
    • Article
    • Peer Reviewed
    UC San Diego Previously Published Works (2020)
    This study aims to quantify changes in outdoor (ambient) air pollution exposure from different migration patterns within Peru and quantify its effect on premature mortality. Data on ambient fine particulate matter (PM2.5) was obtained from the National Aeronautics and Space Administration (NASA). Census data was used to calculate rates of within-country migration at the district level. We calculated differences in PM2.5 exposure between "current" (2016-2017) and "origin" (2012) districts for each migration patterns. Using an exposure-response relationship for PM2.5 extracted from a meta-analysis, and mortality rates from the Peruvian Ministry of Health, we quantified premature mortality attributable to each migration pattern. Changes in outdoor PM2.5 exposure were observed between 2012 and 2016 with highest levels of PM2.5 in the Department of Lima. A strong spatial autocorrelation of outdoor PM2.5 values (Moran's I = 0.847, p-value=0.001) was observed. In Greater Lima, rural-to-urban and urban-to-urban migrants experienced 10-fold increases in outdoor PM2.5 exposure in comparison with non-migrants. Changes in outdoor PM2.5 exposure due to migration drove 137.1 (95%CI: 93.2, 179.4) premature deaths related to air pollution, with rural-urban producing the highest risk of mortality from exposure to higher levels of ambient air pollution. Our results demonstrate that the rural-urban and urban-urban migrant groups have higher rates of air pollution-related deaths.
      Cover page: Revealing the air pollution burden associated with internal Migration in Peru
      • Article
      • Peer Reviewed
      UC San Diego Previously Published Works (2021)
      Access to safe water and basic sanitation and hygiene facilities (WASH) are important for childhood health globally. However, inequalities in WASH access persist, and local governments need to better understand the potential impact of scaling up WASH services on childhood health. Using 2011 Peru Demographic and Health Survey data as a case study, we applied a modified substitution estimator approach to assess the impact of scaling up access (20-100%) to WASH on diarrhea prevalence among children < 5 years. The modified substitution estimator approach can help identify population subgroups or areas where WASH interventions and sustained implementation could be most beneficial and reduce existing disparities. Using findings from a recent meta-analysis and computing bootstrapped estimates and 95% CIs, we examined inequalities in the effect of WASH on self-reported diarrhea by urbanicity, maternal education level, household wealth, and district of residence. Increasing access (100% change) to improved water sources, sanitation, and hygiene facilities reduced population-level prevalence of childhood diarrhea by 8.2% (95% CI: 4.1, 12.3), 5.5% (95% CI: 0.7, 9.8), and 5.2% (95% CI: 2.2, 8.1), respectively. In stratified analyses, increased access to improved water sources and hygiene facilities was associated with decreased prevalence of diarrhea, with the largest reduction in rural areas and households with lower maternal education and lower wealth. Our findings suggest targeted WASH implementation in Peru is needed in rural areas and among lower socioeconomic-status households. In addition, even low levels of change in overall WASH access may decrease diarrhea prevalence.
        Cover page: Modeling the Impact of Population Intervention Strategies on Reducing Health Disparities: Water, Sanitation, and Hygiene Interventions and Childhood Diarrheal Disease in Peru.
        • Article
        • Peer Reviewed
        UCLA Previously Published Works (2024)
        Extreme heat and wildfire smoke events are increasingly co-occurring in the context of climate change, especially in California. Extreme heat and wildfire smoke may have synergistic effects on population health that vary over space. We leveraged high-resolution satellite and monitoring data to quantify spatially varying compound exposures to extreme heat and wildfire smoke in California (2006-2019) at ZIP Code Tabulation Area (ZCTA) level. We found synergistic effects between extreme heat and wildfire smoke on daily cardiorespiratory hospitalizations at the state level. We also found spatial heterogeneity in such synergistic effects across ZCTAs. Communities with lower education attainment, lower health insurance coverage, lower income, lower proportion of automobile ownership, lower tree canopy coverage, higher population density, and higher proportions of racial/ethnic minorities experienced higher synergistic effects. This study highlights the need to incorporate compound hazards and environmental justice considerations into evidence-based policy development to protect populations from increasingly prevalent compound hazards.
          Cover page: Exploring spatial heterogeneity in synergistic effects of compound climate hazards: Extreme heat and wildfire smoke on cardiorespiratory hospitalizations in California.
          • Article
          • Peer Reviewed
          UC San Diego Previously Published Works (2023)

          Background

          Policies to restrict population mobility are a commonly used strategy to limit the transmission of contagious diseases. Among measures implemented during the COVID-19 pandemic were dynamic stay-at-home orders informed by real-time, regional-level data. California was the first state in the U.S. to implement this novel approach; however, the effectiveness of California's four-tier system on population mobility has not been quantified.

          Methods

          Utilizing data from mobile devices and county-level demographic data, we evaluated the impact of policy changes on population mobility and explored whether demographic characteristics explained variability in responsiveness to policy changes. For each California county, we calculated the proportion of people staying home and the average number of daily trips taken per 100 persons, across different trip distances and compared this to pre-COVID-19 levels.

          Results

          We found that overall mobility decreased when counties moved to a more restrictive tier and increased when moving to a less restrictive tier, as the policy intended. When placed in a more restrictive tier, the greatest decrease in mobility was observed for shorter and medium-range trips, while there was an unexpected increase in the longer trips. The mobility response varied by geographic region, as well as county-level median income, gross domestic product, economic, social, and educational contexts, the prevalence of farms, and recent election results.

          Conclusions

          This analysis provides evidence of the effectiveness of the tier-based system in decreasing overall population mobility to ultimately reduce COVID-19 transmission. Results demonstrate that socio-political demographic indicators drive important variability in such patterns across counties.
            Cover page: The role of the California tier system in controlling population mobility during the COVID-19 pandemic
            • Article
            • Peer Reviewed
            UC San Diego Previously Published Works (2019)

            Background

            Exposure to fine particulate matter (PM2.5) during pregnancy has been shown to be associated with reduced birth weight and racial/ethnic minorities have been found to be more vulnerable. Previous studies have focused on the mean value of birth weight associated with PM2.5, which may mask meaningful differences. We applied a quantile regression approach to investigate the variation by percentile of birth weight and compared non-Hispanic (NH) Black, NH White, and Hispanic mothers.

            Methods

            Data for singleton births in California from October 24, 2005 to February 27, 2010 were collected from the birth records accessed from the California Department of Public Health. Air pollution monitoring data collected by the California Air Resources Board and interpolated for each zip code using an inverse-distance weighting approach, and linked to maternal zip code of residence reported on the birth certificate. Multilevel linear regression models were conducted with mother's residential zip code tabulation area as a random effect. Multilevel quantile regression models were used to analyze the association at different percentiles of birth weight (5th, 10th, 25th, 50th, 75th, 90th, 95th), as well as examine the heterogeneity in this association between racial/ethnic groups.

            Results

            Linear regression revealed that a 10 μg/m3 increase in PM2.5 exposure during pregnancy is associated with a mean birth weight decrease of 7.31 g [95% confidence interval (CI): 8.10, 6.51] and NH Black mothers are the most vulnerable. Results of the quantile regression are not constant across quantiles. For NH Black mothers whose infants had the lowest birthweight of less than 2673 g (5th percentile), a 10 μg/m3 increase in PM2.5 exposure is associated with a decrease of 18.57 g [95% CI: 22.23, 14.91], while it is associated with a decrease of 7.77 g [95% CI: 8.73, 6.79] for NH White mothers and 7.76 [8.52, 7.00] decrease for Hispanic mothers at the same quantile.

            Conclusion

            Results of the quantile regression revealed greater disparities, particularly for infants with the lowest birth weight. By identifying vulnerable populations, we can promote and implement policies to confront these health disparities.
              • Article
              • Peer Reviewed
              UC San Diego Previously Published Works (2018)
              The epidemiological evidence demonstrating the effect of disinfection by-products (DBPs) from drinking water on colon and rectal cancers is well documented. However, no systematic assessment has been conducted to assess the potential effect measure modification (EMM) in the relationship between DBPs and cancer. The objective of this paper is to conduct a systematic literature review to determine the extent to which EMM has been assessed in the relationship between DBPs in drinking water in past epidemiological studies. Selected articles (n = 19) were reviewed, and effect estimates and covariates that could have been used in an EMM assessment were gathered. Approximately half of the studies assess EMM (n = 10), but the majority of studies only estimate it relative to sex subgroups (n = 6 for bladder cancer and n = 2 both for rectal and colon cancers). Although EMM is rarely assessed, several variables that could have a potential modification effect are routinely collected in these studies, such as socioeconomic status or age. The role of environmental exposures through drinking water can play an important role and contribute to cancer disparities. We encourage a systematic use of subgroup analysis to understand which populations or territories are more vulnerable to the health impacts of DBPs.
                Cover page: Heterogeneity in the Relationship between Disinfection By-Products in Drinking Water and Cancer: A Systematic Review
                • Article
                • Peer Reviewed
                UC Irvine Previously Published Works (2020)
                Exposure to high air temperature in late pregnancy is increasingly recognized as a risk factor for preterm birth (PTB). However, the combined effects of heatwaves with air pollution and green space are still unexplored. In the context of climate change, investigating the interaction between environmental factors and identifying communities at higher risk is important to better understand the etiological mechanisms and design targeted interventions towards certain women during pregnancy. To examine the combined effects of heatwaves, air pollution and green space exposure on the risk of PTB. California birth certificate records for singleton births (2005-2013) were obtained. Residential zip code-specific daily temperature during the last week of gestation was used to create 12 definitions of heatwave with varying temperature thresholds and durations. We fit multi-level Cox proportional hazard models with time to PTB as the outcome and gestational week as the temporal unit. Relative risk due to interaction (RERI) was applied to estimate the additive interactive effect of air pollution and green space on the effect of heatwaves on PTB. In total, 1,967,300 births were included in this study. For PM2.5, PM10 and O3, we found positive additive interactions (RERIs >0) between heatwaves and higher air pollution levels. Combined effects of heatwaves and green space indicated negative interactions (RERIs <0) for less intense heatwaves (i.e., shorter duration or relatively low temperature), whereas there were potential positive interactions (RERIs >0) for more intense heatwaves. This study found synergistic harmful effects for heatwaves with air pollution, and potential positive interactions with lack of green space on PTB. Implementing interventions, such as heat warning systems and behavioral changes, targeted toward pregnant women at risk for high air pollution and low green space exposures may optimize the benefits of reducing acute exposure to extreme heat before delivery.
                  Cover page: Examining the joint effects of heatwaves, air pollution, and green space on the risk of preterm birth in California
                  • Article
                  • Peer Reviewed
                  UCLA Previously Published Works (2021)
                  Santa Ana winds (SAWs) are associated with anomalous temperatures in coastal Southern California (SoCal). As dry air flows over SoCal's coastal ranges on its way from the elevated Great Basin down to sea level, all SAWs warm adiabatically. Many but not all SAWs produce coastal heat events. The strongest regionally averaged SAWs tend to be cold. In fact, some of the hottest and coldest observed temperatures in coastal SoCal are linked to SAWs. We show that hot and cold SAWs are produced by distinct synoptic dynamics. High-amplitude anticyclonic flow around a blocking high pressure aloft anchored at the California coast produces hot SAWs. Cold SAWs result from anticyclonic Rossby wave breaking over the northwestern U.S. Hot SAWs are preceded by warming in the Great Basin and dry conditions across the Southwestern U.S. Precipitation over the Southwest, including SoCal, and snow accumulation in the Great Basin usually precede cold SAWs. Both SAW flavors, but especially the hot SAWs, yield low relative humidity at the coast. Although cold SAWs tend to be associated with the strongest winds, hot SAWs tend to last longer and preferentially favor wildfire growth. Historically, out of large (> 100 acres) SAW-spread wildfires, 90% were associated with hot SAWs, accounting for 95% of burned area. As health impacts of SAW-driven coastal fall, winter and spring heat waves and impacts of smoke from wildfires have been recently identified, our results have implications for designing early warning systems. The long-term warming trend in coastal temperatures associated with SAWs is focused on January-March, when hot and cold SAW frequency and temperature intensity have been increasing and decreasing, respectively, over our 71-year record.

                  Supplementary information

                  The online version contains supplementary material available at 10.1007/s00382-021-05802-z.
                    Top