Impacts of heat and wildfire on preterm birth.

BACKGROUND: Climate change continues to increase the frequency, intensity, and duration of heat events and wildfires, both of which are associated with adverse pregnancy outcomes. Few studies simultaneously evaluated exposures to these increasingly common exposures. OBJECTIVES: We investigated the relationship between exposure to heat and wildfire smoke and preterm birth (PTB). METHODS: In this time-stratified case-crossover study, participants consisted of 85,806 California singleton PTBs (20-36 gestational weeks) from May through October of 2015-2019. Birthing parent ZIP codes were linked to high-resolution daily weather, PM2.5 from wildfire smoke, and ambient air pollution data. Heat day was defined as a day with apparent temperature >98th percentile within each ZIP code and heat wave was defined as ≥2 consecutive heat days. Wildfire-smoke day was defined as a day with any exposure to wildfire-smoke PM2.5. Conditional logistic regression was used to calculate the odds ratio (OR) and 95% confidence intervals (CI) comparing exposures during a hazard period (lags 0-6) compared to control periods. Analyses were adjusted for relative humidity, fine particles, and ozone. RESULTS: Wildfire-smoke days were associated with 3.0% increased odds of PTB (ORlag0: 1.03, CI: 1.00-1.05). Compared with white participants, associations appeared stronger among Black, Hispanic, Asian, and American Indians/Alaskan Native participants. Heatwave days (ORlag2: 1.07, CI: 1.02-1.13) were positively associated with PTB, with stronger associations among those simultaneously exposed to wildfire smoke days (ORlag2: 1.19, CI: 1.11-1.27). Similar findings were observed for heat days and when other temperature metrics (e.g., maximum, minimum) were used. DISCUSSION: Heat and wildfire increased PTB risk with evidence of synergism. As the occurrence and co-occurrence of these events increase, exposure reduction among pregnant people is critical, especially among racial/ethnic minorities.

Adverse effects of temperature on perinatal and pregnancy outcomes: methodological challenges and knowledge gaps.

Evidence linking temperature with adverse perinatal and pregnancy outcomes is emerging. We searched for literature published until 30 January 2023 in PubMed, Web of Science, and reference lists of articles focusing on the outcomes that were most studied like preterm birth, low birth weight, stillbirth, and hypertensive disorders of pregnancy. A review of the literature reveals important gaps in knowledge and several methodological challenges. One important gap is the lack of knowledge of how core body temperature modulates under extreme ambient temperature exposure during pregnancy. We do not know the magnitude of non-modulation of body temperature during pregnancy that is clinically significant, i.e., when the body starts triggering physiologic counterbalances. Furthermore, few studies are conducted in places where extreme temperature conditions are more frequently encountered, such as in South Asia and sub-Saharan Africa. Little is also known about specific cost-effective interventions that can be implemented in vulnerable communities to reduce adverse outcomes. As the threat of global warming looms large, effective interventions are critically necessary to mitigate its effects.

The Burden of Wildfire Smoke on Respiratory Health in California at the Zip Code Level: Uncovering the Disproportionate Impacts of Differential Fine Particle Composition.

Wildfires constitute a growing source of extremely high levels of particulate matter that is less than 2.5 microns in diameter (PM2.5). Recently, toxicologic and epidemiologic studies have shown that PM2.5 generated from wildfires may have a greater health burden than PM2.5 generated from other pollutant sources. This study examined the impact of PM2.5 on hospitalizations for respiratory diseases in California between 2006 and 2019 using a health impact assessment approach that considers differential concentration-response functions (CRF) for PM2.5 from wildfire and non-wildfire sources of emissions. We quantified the burden of respiratory hospitalizations related to PM2.5 exposure at the zip code level through two different approaches: (a) naïve (considering the same CRF for all PM2.5 emissions) and (b) nuanced (considering different CRFs for PM2.5 from wildfires and from other sources). We conducted a Geographically Weighted Regression to analyze spatially varying relationships between the delta (i.e., the difference between the naïve and nuanced approaches) and the Centers for Disease Control and Prevention's Social Vulnerability Index (SVI). A higher attributable number of respiratory hospitalizations was found when accounting for the larger health burden of wildfire PM2.5. We found that, between 2006 and 2019, the number of hospitalizations attributable to PM2.5 may have been underestimated by approximately 13% as a result of not accounting for the higher CRF of wildfire-related PM2.5 throughout California. This underestimation was higher in northern California and areas with higher SVI rankings. The relationship between delta and SVI varied spatially across California. These findings can be useful for updating future air pollution guideline recommendations.

Climate change: Overview of risks to pregnant persons and their offspring.

Climate change is one of the greatest challenges confronting humanity. Pregnant persons, their unborn children, and offspring are particularly vulnerable, as evidenced by adverse perinatal outcomes and increased rates of childhood illnesses. Environmental inequities compound the problem of maternal health inequities, and have given rise to the environmental justice movement.  The International Federation of Gynecology and Obstetrics and other major medical societies have worked to heighten awareness and address the deleterious health effects of climate change and toxic environmental exposures. As part of routine prenatal, neonatal, and pediatric care, neonatal-perinatal care providers should incorporate discussions with their patients and families on potential harms and also identify actions to mitigate climate change effects on their health. This article provides clinicians with an overview of how climate change affects their patients, practical guidance in caring for them, and a frame setting of the articles to follow. Clinicians have a critical role to play, and the time to act is now.

Emergency department visits associated with wildfire smoke events in California, 2016-2019.

Wildfire smoke has been associated with adverse respiratory outcomes, but the impacts of wildfire on other health outcomes and sensitive subpopulations are not fully understood. We examined associations between smoke events and emergency department visits (EDVs) for respiratory, cardiovascular, diabetes, and mental health outcomes in California during the wildfire season June-December 2016-2019. Daily, zip code tabulation area-level wildfire-specific fine particulate matter (PM2.5) concentrations were aggregated to air basins. A "smoke event" was defined as an air basin-day with a wildfire-specific PM2.5 concentration at or above the 98th percentile across all air basin-days (threshold = 13.5 µg/m3). We conducted a two-stage time-series analysis using quasi-Poisson regression considering lag effects and random effects meta-analysis. We also conducted analyses stratified by race/ethnicity, age, and sex to assess potential effect modification. Smoke events were associated with an increased risk of EDVs for all respiratory diseases at lag 1 [14.4%, 95% confidence interval (CI): (6.8, 22.5)], asthma at lag 0 [57.1% (44.5, 70.8)], and chronic lower respiratory disease at lag 0 [12.7% (6.2, 19.6)]. We also found positive associations with EDVs for all cardiovascular diseases at lag 10. Mixed results were observed for mental health outcomes. Stratified results revealed potential disparities by race/ethnicity. Short-term exposure to smoke events was associated with increased respiratory and schizophrenia EDVs. Cardiovascular impacts may be delayed compared to respiratory outcomes.

A novel ensemble-based statistical approach to estimate daily wildfire-specific PM2.5 in California (2006-2020).

Though fine particulate matter (PM2.5) has decreased in the United States (U.S.) in the past two decades, the increasing frequency, duration, and severity of wildfires significantly (though episodically) impairs air quality in wildfire-prone regions and beyond. Increasing PM2.5 concentrations derived from wildfire smoke and associated impacts on public health require dedicated epidemiological studies. Main sources of PM2.5 data are provided by government-operated monitors sparsely located across U.S., leaving several regions and potentially vulnerable populations unmonitored. Current approaches to estimate PM2.5 concentrations in unmonitored areas often rely on big data, such as satellite-derived aerosol properties and meteorological variables, apply computationally-intensive deterministic modeling, and do not distinguish wildfire-specific PM2.5 from other sources of emissions such as traffic and industrial sources. Furthermore, modelling wildfire-specific PM2.5 presents a challenge since measurements of the smoke contribution to PM2.5 pollution are not available. Here, we aim to use statistical methods to isolate wildfire-specific PM2.5 from other sources of emissions. Our study presents an ensemble model that optimally combines multiple machine learning algorithms (including gradient boosting machine, random forest and deep learning), and a large set of explanatory variables to, first, estimate daily PM2.5 concentrations at the ZIP code level, a relevant spatiotemporal resolution for epidemiological studies. Subsequently, we propose a novel implementation of an imputation approach to estimate the wildfire-specific PM2.5 concentrations that could be applied geographical regions in the US or worldwide. Our ensemble model achieved comparable results to previous machine learning studies for PM2.5 prediction while avoiding processing larger, computationally intensive datasets. Our study is the first to apply a suite of statistical models using readily available datasets to provide daily wildfire-specific PM2.5 at a fine spatial scale for a 15-year period, thus providing a relevant spatiotemporal resolution and timely contribution for epidemiological studies.

Regional Research-Practice-Policy Partnerships in Response to Climate-Related Disparities: Promoting Health Equity in the Pacific.

Although climate change poses a threat to health and well-being globally, a regional approach to addressing climate-related health equity may be more suitable, appropriate, and appealing to under-resourced communities and countries. In support of this argument, this commentary describes an approach by a network of researchers, practitioners, and policymakers dedicated to promoting climate-related health equity in Small Island Developing States and low- and middle-income countries in the Pacific. We identify three primary sets of needs related to developing a regional capacity to address physical and mental health disparities through research, training, and assistance in policy and practice implementation: (1) limited healthcare facilities and qualified medical and mental health providers; (2) addressing the social impacts related to the cooccurrence of natural hazards, disease outbreaks, and complex emergencies; and (3) building the response capacity and resilience to climate-related extreme weather events and natural hazards.

Impacts of Fine Particulate Matter From Wildfire Smoke on Respiratory and Cardiovascular Health in California.

Increases in wildfire activity across the Western US pose a significant public health threat. While there is evidence that wildfire smoke is detrimental for respiratory health, the impacts on cardiovascular health remain unclear. This study evaluates the association between fine particulate matter (PM2.5) from wildfire smoke and unscheduled cardiorespiratory hospital visits in California during the 2004-2009 wildfire seasons. We estimate daily mean wildfire-specific PM2.5 with Goddard Earth Observing System-Chem, a global three-dimensional model of atmospheric chemistry, with wildfire emissions estimates from the Global Fire Emissions Database. We defined a "smoke event day" as cumulative 0-1-day lag wildfire-specific PM2.5 ≥ 98th percentile of cumulative 0-1 lag day wildfire PM2.5. Associations between exposure and outcomes are estimated using negative binomial regression. Results indicate that smoke event days are associated with a 3.3% (95% CI: [0.4%, 6.3%]) increase in visits for all respiratory diseases and a 10.3% (95% CI: [2.3%, 19.0%]) increase for asthma specifically. Stratifying by age, we found the largest effect for asthma among children ages 0-5 years. We observed no significant association between exposure and overall cardiovascular disease, but stratified analyses revealed increases in visits for all cardiovascular, ischemic heart disease, and heart failure among non-Hispanic white individuals and those older than 65 years. Further, we found a significant interaction between smoke event days and daily average temperature for all cardiovascular disease visits, suggesting that days with high wildfire PM2.5 concentrations and high temperatures may pose greater risk for cardiovascular disease. These results suggest substantial increases in adverse outcomes from wildfire smoke exposure and indicate the need for improved prevention strategies and adaptations to protect vulnerable populations.

Spatial variation in the joint effect of extreme heat events and ozone on respiratory hospitalizations in California.

Extreme heat and ozone are co-occurring exposures that independently and synergistically increase the risk of respiratory disease. To our knowledge, no joint warning systems consider both risks; understanding their interactive effect can warrant use of comprehensive warning systems to reduce their burden. We examined heterogeneity in joint effects (on the additive scale) between heat and ozone at small geographical scales. A within-community matched design with a Bayesian hierarchical model was applied to study this association at the zip code level. Spatially varying relative risks due to interaction (RERI) were quantified to consider joint effects. Determinants of the spatial variability of effects were assessed using a random effects metaregression to consider the role of demographic/neighborhood characteristics that are known effect modifiers. A total of 817,354 unscheduled respiratory hospitalizations occurred in California from 2004 to 2013 in the May to September period. RERIs revealed no additive interaction when considering overall joint effects. However, when considering the zip code level, certain areas observed strong joint effects. A lower median income, higher percentage of unemployed residents, and exposure to other air pollutants within a zip code drove stronger joint effects; a higher percentage of commuters who walk/bicycle, a marker for neighborhood wealth, showed decreased effects. Results indicate the importance of going beyond average measures to consider spatial variation in the health burden of these exposures and predictors of joint effects. This information can be used to inform early warning systems that consider both heat and ozone to protect populations from these deleterious effects in identified areas.

The association between ozone and fine particles and mental health-related emergency department visits in California, 2005-2013.

Recent studies suggest that air pollutant exposure may increase the incidence of mental health conditions, however research is limited. We examined the association between ozone (O3) and fine particles (PM2.5) and emergency department (ED) visits related to mental health outcomes, including psychosis, neurosis, neurotic/stress, substance use, mood/affective, depression, bipolar, schizotypal/delusional, schizophrenia, self-harm/suicide, and homicide/inflicted injury, from 2005 through 2013 in California. Air monitoring data were provided by the U.S. EPA's Air Quality System Data Mart and ED data were provided by the California Office of Statewide Health Planning and Development. We used the time-series method with a quasi-Poisson regression, controlling for apparent temperature, day of the week, holidays, and seasonal/long-term trends. Per 10 parts per billion increase, we observed significant cumulative 7-day associations between O3 and all mental health [0.64%, 95% confidence interval (CI): 0.21, 1.07], depression [1.87%, 95% CI: 0.62, 3.15], self-harm/suicide [1.43%, 95% CI: 0.35, 2.51], and bipolar [2.83%, 95% CI: 1.53, 4.15]. We observed 30-day lag associations between O3 and neurotic disorder [1.22%, 95% CI: 0.48, 1.97] and homicide/inflicted injury [2.01%, 95% CI: 1.00, 3.02]. Same-day mean PM2.5 was associated with a 0.42% [95% CI: 0.14, 0.70] increase in all mental health, 1.15% [95% CI: 0.62, 1.69] increase in homicide/inflicted injury, and a 0.57% [95% CI: 0.22, 0.92] increase in neurotic disorders per 10 µg/m3 increase. Other outcomes not listed here were not statistically significant for O3 or PM2.5. Risk varied by age group and was generally greater for females, Asians, and Hispanics. We also observed seasonal variation for outcomes including but not limited to depression, bipolar, schizophrenia, self-harm/suicide, and homicide/inflicted injury. Ambient O3 or PM2.5 may increase the risk of mental health illness, though underlying biological mechanisms remain poorly understood. Findings warrant further investigation to better understand the impacts of air pollutant exposure among vulnerable groups.

Racial/ethnic disparities in the association between fine particles and respiratory hospital admissions in San Diego county, CA.

Ambient air pollution exposure is associated with exacerbating respiratory illnesses. Race/ethnicity (R/E) have been shown to influence an individual's vulnerability to environmental health risks such as fine particles (PM 2.5). This study aims to assess the R/E disparities in vulnerability to air pollution with regards to respiratory hospital admissions in San Diego County, California where most days fall below National Ambient Air Quality Standards (NAAQS) for daily PM 2.5 concentrations. Daily PM 2.5 levels were estimated at the zip code level using a spatial interpolation using inverse-distance weighting from monitor networks. The association between daily PM 2.5 levels and respiratory hospital admissions in San Diego County over a 15-year period from 1999 to 2013 was assessed with a time-series analysis using a multi-level Poisson regression model. Cochran Q tests were used to assess the effect modification of race/ethnicity on this association. Daily fine particle levels varied greatly from 1 µg/m3 to 75.86 µg/m3 (SD = 6.08 µg/m3) with the majority of days falling below 24-hour NAAQS for PM 2.5 of 35 µg/m3. For every 10 µg/m3 increase in PM 2.5 levels, Black and White individuals had higher rates (8.6% and 6.2%, respectively) of hospitalization for respiratory admissions than observed in the county as a whole (4.1%). Increases in PM 2.5 levels drive an overall increase in respiratory hospital admissions with a disparate burden of health effects by R/E group. These findings suggest an opportunity to design interventions that address the unequal burden of air pollution among vulnerable communities in San Diego County that exist even below NAAQS for daily PM 2.5 concentrations.

Examining fine particulate matter and cause-specific morbidity during the 2017 North San Francisco Bay wildfires.

BACKGROUND: Recent increases in wildfire frequency and severity necessitate better understanding of health effects of wildfire smoke to protect affected populations. OBJECTIVES: We examined relationships between fine particulate matter (PM2.5) and morbidity during wildfires in California, and whether those relationships differed during the fire compared to a similar non-fire period. METHODS: For nine San Francisco Bay Area counties, daily county-level diagnosis-specific counts of emergency department visits (EDVs) and hospitalizations were linked with county-level estimates of daily mean PM2.5 during the October 2017 Northern California wildfires and similar October days in 2015, 2016, and 2017. Associations were estimated using Poisson regression. RESULTS: The median difference between county PM2.5 during the fire versus the non-fire period was 23.4 µg/m3, with days exceeding 80 µg/m3 in some counties. Over the entire study period, PM2.5 was most consistently linked to EDVs for respiratory disease (RREDV(lag0) per 23.4 µg/m3 increase: 1.25, 95% CI: 1.21, 1.30), asthma, chronic lower respiratory disease (CLRD; RREDV(lag0): 1.18, 95% CI: 1.10, 1.27), and acute myocardial infarction (RREDV(lag0): 1.14, 95% CI: 1.03, 1.25). Increases in acute upper respiratory infections and decreases in mental/behavioral EDVs were observed but were sensitive to model specification, specifically the inclusion of time-related covariates. Comparing fire and non-fire period EDV associations, we observed indications that PM2.5 during the fire was more strongly associated with asthma (RRlag0: 1.46, 95% CI: 1.38, 1.55) compared to non-fire period PM2.5 (RRlag0: 0.77, 95% CI: 0.55, 1.08), and the opposite observed for dysrhythmia, with the asthma difference being particularly robust to model choice. For hospitalizations, the most robust PM2.5 relationships were positive associations with respiratory, CLRD, and diabetes, and inverse associations with pneumonia. Respiratory and CLRD effect estimates were generally similar or smaller than for EDVs. CONCLUSIONS: Elevated short-term PM2.5 levels from wildfire smoke appears to impact respiratory and other health domains.

Association between coarse particulate matter and inflammatory and hemostatic markers in a cohort of midlife women.

BACKGROUND: Exposure to particulate matter air pollution has been associated with cardiovascular disease (CVD) morbidity and mortality; however, most studies have focused on fine particulate matter (PM2.5) exposure and CVD. Coarse particulate matter (PM10-2.5) exposure has not been extensively studied, particularly for long-term exposure, and the biological mechanisms remain uncertain. METHODS: We examined the association between ambient concentrations of PM10-2.5 and inflammatory and hemostatic makers that have been linked to CVD. Annual questionnaire and clinical data were obtained from 1694 women (≥ 55 years old in 1999) enrolled in the longitudinal Study of Women's Health Across the Nation (SWAN) at six study sites from 1999 to 2004. Residential locations and the USEPA air monitoring network measurements were used to assign exposure to one-year PM10-2.5, as well as co-pollutants. Linear mixed-effects regression models were used to describe the association between PM10-2.5 exposure and markers, including demographic, health and other covariates. RESULTS: Each interquartile (4 µg/m3) increase in one-year PM10-2.5 exposure was associated with a 5.5% (95% confidence interval [CI]: 1.8, 9.4%) increase in levels of plasminogen activator inhibitor-1 (PAI-1) and 4.1% (95% CI: - 0.1, 8.6%) increase in high-sensitivity C-creative Protein (hs-CRP). Stratified analyses suggested that the association with PAI-1 was particularly strong in some subgroups, including women who were peri-menopausal, were less educated, had a body mass index lower than 25, and reported low alcohol consumption. The association between PM10-2.5 and PAI-1 remained unchanged with adjustment for PM2.5, ozone, nitrogen dioxide, and carbon monoxide. CONCLUSIONS: Long-term PM10-2.5 exposure may be associated with changes in coagulation independently from PM2.5, and thus, contribute to CVD risk in midlife women.

A case-crossover study of short-term air pollution exposure and the risk of stillbirth in California, 1999-2009.

BACKGROUND: Associations between ambient air pollution and stillbirth have recently been explored, but most studies have focused on long-term (trimester or gestational averages) rather than short-term (within one week) air pollution exposures. OBJECTIVE: To evaluate whether short-term exposures to criteria air pollutants are associated with increased risk of stillbirth. METHODS: Using air pollution and fetal death certificate data from 1999 to 2009, we assessed associations between acute prenatal air pollution exposure and stillbirth in California. In a time-stratified case-crossover study, we analyzed single day and/or cumulative average days (up to a 6 day lag) of exposure to fine (PM2.5) and coarse particles (PM10-2.5), ozone (O3), nitrogen dioxide (NO2), sulfur dioxide (SO2), and carbon monoxide (CO) for mothers estimated to reside within 10 km of a pollution monitor based on reported zip code. We also examined potential confounding by apparent temperature or co-pollutants, and effect modification by maternal demographic factors, fetal sex, gestational age, and cause of stillbirth. RESULTS: Stillbirth cases in the primary analyses ranged between 1,203 and 13,018, depending on the pollutant. For an IQR increase in SO2 (lag 4), O3 (lag 4), and PM10-2.5 (lag 2), we found a 2.8% (95% confidence interval (CI) 0.2%, 5.5%), 5.8% (95% CI 1.6%, 10.1%), and 6.1% (95% CI 0.1%, 12.4%) increase in the odds of stillbirth, respectively. Additional adjustment by apparent temperature had little effect on the SO2 association but slightly attenuated O3 (adjusted % change: 4.2% (95% CI -0.2%, 8.9%) and PM10-2.5 (5.7% (95% CI -1.1%, 13.0%)) associations, while other co-pollutants had minimal impact. Associations were observed specifically for stillbirths from obstetric complications and in women with higher educational attainment. CONCLUSIONS: This study provides evidence for associations between prenatal short-term air pollution exposure, specifically SO2, O3, and PM10-2.5, and stillbirth in California and warrants replication of findings in other settings.

Examining the relationship between ambient carbon monoxide, nitrogen dioxide, and mental health-related emergency department visits in California, USA.

Growing evidence suggests air pollutants may harm the central nervous system, potentially impacting mental health. However, such impacts of air pollutants on mental health and the sub-populations most affected remain poorly understood, especially in California. We examined the relationship between short-term ambient carbon monoxide (CO), nitrogen dioxide (NO2), and mental health-related emergency department (ED) visits in California from 2005 to 2013. Daily mean concentrations of the pollutants were acquired from the U.S. Environmental Protection Agency Air Quality System Data Mart ground monitoring data. Moving averages of pollutant concentrations were linked to counts of ED visits obtained from the California Office of Statewide Health Planning and Development. Seven mental health outcomes, defined by International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) codes, were studied: all mental disorders, bipolar disorder, depression, schizophrenia, substance abuse, homicide/inflicted injury, and suicide/self-harm. Monitor-level associations were estimated with quasi-Poisson regression models and combined using random-effects meta-analysis. CO and NO2 were found to be positively associated with ED visits due to homicide/inflicted injury, with the warm season (May-October) driving the CO association. An interquartile range (IQR) (0.28 ppm) increase in two-day average CO during the warm season was associated with a 3.13% (95% confidence interval (CI): 1.43, 4.84) elevation in risk of an ED visit due to homicide/inflicted injury (n = 122,749 ED visits). An IQR (10.79 ppb) increase in two-day average NO2 was associated with a 2.60% (95% CI: 1.17, 4.05) elevation in risk of an ED visit due to homicide/inflicted injury (n = 206,919 ED visits). Subgroup analyses indicated children, Hispanics, and males were particularly vulnerable. Except for an inverse relationship between NO2 and substance abuse, neither pollutant was robustly associated with visits due to other mental health morbidities. Our results suggest short-term elevations in CO and NO2 may promote violent behavior. Further investigation in other populations and ranges of air pollution exposure is warranted.

Association of Air Pollution and Heat Exposure With Preterm Birth, Low Birth Weight, and Stillbirth in the US: A Systematic Review.

Importance: Knowledge of whether serious adverse pregnancy outcomes are associated with increasingly widespread effects of climate change in the US would be crucial for the obstetrical medical community and for women and families across the country. Objective: To investigate prenatal exposure to fine particulate matter (PM2.5), ozone, and heat, and the association of these factors with preterm birth, low birth weight, and stillbirth. Evidence Review: This systematic review involved a comprehensive search for primary literature in Cochrane Library, Cochrane Collaboration Registry of Controlled Trials, PubMed, ClinicalTrials.gov website, and MEDLINE. Qualifying primary research studies included human participants in US populations that were published in English between January 1, 2007, and April 30, 2019. Included articles analyzed the associations between air pollutants or heat and obstetrical outcomes. Comparative observational cohort studies and cross-sectional studies with comparators were included, without minimum sample size. Additional articles found through reference review were also considered. Articles analyzing other obstetrical outcomes, non-US populations, and reviews were excluded. Two reviewers independently determined study eligibility. The Arskey and O'Malley scoping review framework was used. Data extraction was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) reporting guideline. Findings: Of the 1851 articles identified, 68 met the inclusion criteria. Overall, 32 798 152 births were analyzed, with a mean (SD) of 565 485 (783 278) births per study. A total of 57 studies (48 of 58 [84%] on air pollutants; 9 of 10 [90%] on heat) showed a significant association of air pollutant and heat exposure with birth outcomes. Positive associations were found across all US geographic regions. Exposure to PM2.5 or ozone was associated with increased risk of preterm birth in 19 of 24 studies (79%) and low birth weight in 25 of 29 studies (86%). The subpopulations at highest risk were persons with asthma and minority groups, especially black mothers. Accurate comparisons of risk were limited by differences in study design, exposure measurement, population demographics, and seasonality. Conclusions and Relevance: This review suggests that increasingly common environmental exposures exacerbated by climate change are significantly associated with serious adverse pregnancy outcomes across the US.

Temperature and hand, foot and mouth disease in California: An exploratory analysis of emergency department visits by season, 2005-2013.

BACKGROUND: For the past decade, hand, foot and mouth disease (HFMD), caused by entero and coxsackie viruses, has been spreading in Asia, particularly among children, overloading healthcare settings and creating economic hardships for parents. Recent studies have found meteorological factors, such as temperature, are associated with HFMD in Asia. However, few studies have explored the relationship in the United States, although HFMD cases have steadily increased recently. As concerns of climate change grow, we explored the association between temperature and HFMD admissions to the Emergency Department (ED) in California. METHODS: Weekly counts of HFMD for 16 California climate zones were collected from 2005 to 2013. We calculated weekly temperature for each climate zone using an inverse distance-weighting method. For each climate zone stratified by season, we conducted a time-series using Poisson regression models. We adjusted models for weekly averaged relative humidity, average number of HFMD cases in previous weeks and long-term temporal trends. Climate zone estimates were combined to obtain an overall seasonal estimate. We attempted stratified analyses by region, race/ethnicity, and sex to identify sensitive subpopulations. RESULTS: Risk of ED visits for HFMD per 1 °F increase in mean temperature during the same week increased 2.00% (95% confidence intervals 1.15, 2.86%) and 2.35% (1.38, 3.33%) during the warm and cold seasons, respectively. The coastal region showed a higher, though not statistically different, association during the cold season [3.18% (1.99, 4.39)] than the warm season [1.64% (0.47, 2.82)]. CONCLUSIONS: Our findings indicated an association between temperature and ED visits for HFMD, with variation by season and region. Thus, the causative pathogen's ability to persist in the atmosphere may vary by season. Furthermore, the mild and wet winter in the coastal region of California may contribute to different results than studies in Asia. With the onset of climate change, HFMD cases will likely grow in California, warranting further investigation on this relationship, including new populations at-risk.

Extreme heat episodes and risk of preterm birth in California, 2005-2013.

BACKGROUND: Preterm birth is a leading cause of infant morbidity and mortality. Identifying potentially modifiable triggers toward the end of gestation, such as extreme heat, can improve understanding of the role of acute stress on early deliveries and inform warning systems. In this study we examined the association between extreme heat, variously defined during the last week of gestation, and risk of preterm birth among mothers in California. METHODS: We created a population-based cohort comprised of 1,967,300 mothers who had live, singleton births in California, from May through September 2005-2013. Daily temperature data estimated at the maternal zip code of residence was used to create 12 definitions of extreme heat with varying relative temperatures (75th, 90th, 95th, and 98th percentiles) and durations (at least 2, 3, or 4 consecutive days). We estimated risk of preterm birth (<37 gestational weeks) in relation to exposure to extreme heat during the last week of gestation with multi-level Cox proportional hazard regression models, adjusting for maternal characteristics, sex of neonate, and seasonality. We also included randomly generated data, SAS code, and estimates for reproducibility purposes. RESULTS: Approximately 7% of the cohort had a preterm birth. For all definitions of extreme heat, the risk of preterm birth was consistently higher among mothers who experienced an extreme heat episode during their last week of gestation. Hazard ratios ranged from 1.008 (95% CI: 0.997, 1.021) to 1.128 (95% CI: 1.052, 1.210), with increasing associations as the relative temperature and duration of extreme heat episode increased. CONCLUSION: This study adds to the previous literature by considering multiple definitions of extreme heat and applying a time-to-event framework. Findings suggest that acute exposure to extreme heat during the last week of gestation may trigger an earlier delivery. Implementing heat warning systems targeted toward pregnant women may improve birth outcomes.