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Letters to the Editor| Volume 30, ISSUE 1, P100-103, March 2019

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Ethnicity-Based Inequality in Heat-Related Illness Is on the Rise in California

Published:January 11, 2019DOI:https://doi.org/10.1016/j.wem.2018.10.001
      To the Editor:
      Climate change is increasingly recognized as one of the biggest emerging threats to human health in the 21st century. The health consequences of climate change are expected to disproportionately affect low-income countries and vulnerable populations in high-income countries, such as the poor and people of color.
      • Levy BS
      • Patz JA
      Climate change, human rights, and social justice.
      It has been previously reported that nonwhite minority groups in the United States have increased vulnerability to heat-related illness.
      • Basu R.
      High ambient temperature and mortality: a review of epidemiologic studies from 2001 to 2008.
      The reasons for this are unclear. The effect is probably multifactorial, including genetic, epigenetic, environmental, social, cultural, and economic factors.
      • Hansen A
      • Bi L
      • Saniotis A
      • Nitschke M
      Vulnerability to extreme heat and climate change: is ethnicity a factor.
      California is the most populous state in the United States

      US Census Bureau. Annual Estimates of the Resident Population, 2010–2016 estimates. Available at: https://factfinder.census.gov/faces/tableservices/jsf/pages/productview.xhtml?pid=PEP_2017_PEPANNRES&prodType=table. Accessed September 12, 2017.

      and the 12th hottest,

      Current results, weather and science facts. Average annual temperature for each US state. Available at: https://www.currentresults.com/Weather/US/average-annual-state-temperatures.php. Accessed September 12, 2017.

      with an average annual temperature of 15.2°C (59.4°F). Some attention has been paid in the literature to heat-related illness, particularly among agricultural workers in California, the majority of whom are Hispanic and black and have an increased risk of occupational heat-related illness relative to the general population.
      • Stoecklin-Marois M
      • Hennessy-Burt T
      • Mitchell D
      • Schenker M
      Heat-related illness knowledge and practices among California hired farm workers in the MICASA study.
      • Mitchell DC
      • Castro J
      • Armitage TL
      • Vega-Arroyo AJ
      • Moyce SC
      • Tancredi DJ
      • et al.
      Recruitment, methods, and descriptive results of a physiologic assessment of Latino farmworkers: the California heat illness prevention study.
      Although the disparity in susceptibility to heat-related illness among ethnicities is well-documented among agriculture workers in previous studies,
      • Fleischer NL
      • Tiesman HM
      • Sumitani J
      • Mize T
      • Amarnath KK
      • Bayakly AR
      • et al.
      Public health impact of heat-related illness among migrant farmworkers.
      • Lam M
      • Krenz J
      • Palmández P
      • Negrete M
      • Perla M
      • Murphy-Robinson H
      • et al.
      Identification of barriers to the prevention and treatment of heat-related illness in Latino farmworkers using activity-oriented, participatory rural appraisal focus group methods.
      • Gronlund C.
      Racial and socioeconomic disparities in heat-related health effects and their mechanisms: a review.
      we were interested in examining whether there was any indication that this susceptibility was improving or worsening over time.
      The state of California's office of statewide health planning and development routinely collects data on hospital discharges from every hospital in California, except for federal hospitals. From 2005, the office of statewide health planning and development also has collected data on emergency department (ED) visits at California hospitals. The data collected include demographic data and diagnoses.
      The California Environmental Health Tracking Program (CEHTP)

      California Environmental Health Tracking Program. Heat-related illness and death data: methods and limitations. Available at: http://cehtp.org/faq/climate_change/heatrelated_illness_and_death_data_methods_and_limitations. Accessed September 12, 2017.

      provides data related to hospitalizations, ED visits, and deaths attributed to heat. The CEHTP heat-related illness and death data set includes cases of heat-related ED visits and hospitalizations in the months of May through September, identified using the following codes from the ninth revision of the International Classification of Disease:
      • 992.0 Heat stroke and sunstroke
      • 992.1 Heat syncope
      • 992.2 Heat cramps
      • 992.3 Heat exhaustion from water depletion
      • 992.4 Heat exhaustion from salt depletion
      • 992.5 Heat exhaustion, unspecified
      • 992.6 Heat fatigue, transient
      • 992.7 Heat edema
      • 992.8 Other specified heat effects
      • 992.9 Unspecified effects of heat and light
      • E900.0 Health effects caused by excessive heat due to weather
      • E900.0 Effect from unknown cause of excessive heat
      Visits resulting from a man-made source of heat (E900.1) are excluded.
      The CEHTP data set was queried for ED visits from 2005 (oldest available) to 2015 (most recent available) for all races/ethnicities, African American/black, Asian American/Pacific Islander, Hispanic/Latino, European American/white, and other. All ages and both sexes were included. Data were reported as a crude rate per 10,000 for each ethnic group.
      Descriptive statistics, including percent relative change, percent absolute change, and ratio of change (relative to all races/ethnicities) were calculated. All statistical analysis was performed using Microsoft Excel for Mac 2011, version 14.7.5 (Microsoft, Redmond, WA) (Figure 1).
      Figure 1.
      Figure 1Percent change in heat-related emergency department visits calculated using visits from the year 2005 as the baseline. The results were stratified by ethnicity.
      The rate of ED presentations for heat-related illness increased by 35% on average from 2005 to 2015 for all ethnicities and by 27% for whites. This increase was higher for minorities such as African Americans (67%), Asian Americans (53%), and Hispanics (63%). Results show that the overall, white, and Hispanic populations follow a similar trajectory until the last 2 y, when the rate in the Hispanic population increases disproportionately, relative to the white population, to match the high rate of other minorities. The trend for African Americans and Asians was always higher than that for the overall and white populations, particularly in the last 4 y, when the gap became more evident.
      Our results suggest that ethnic disparities in heat-related illness in California have increased between 2005 and 2015. The increase in ED presentations is disproportionate for minorities such as African Americans, Asian Americans, and Hispanics relative to the white population. The overall trend shows an increase in presentation during the last few years for all ethnicities, which may be explained by a common risk factor such as increase in peak temperature and heat intensity.
      • Basu R
      • Pearson D
      • Malig B
      • Broadwin R
      • Green R
      The effect of high ambient temperature on emergency room visits.
      The disproportionate increase prompts the search for ethnicity-based factors that affect heat vulnerability.
      Socioeconomic factors are the likely explanation for the increase in ED visits among ethnic minorities. Studies in California and neighboring states have highlighted occupational heat-related illness in the farming setting among immigrants, of which Hispanics make up a significant proportion.
      • Stoecklin-Marois M
      • Hennessy-Burt T
      • Mitchell D
      • Schenker M
      Heat-related illness knowledge and practices among California hired farm workers in the MICASA study.
      Previous cross-sectional studies in California and neighboring states concluded that agriculture workers, composed of largely migrant populations, are at higher risk for heat-related illness.
      • Fleischer NL
      • Tiesman HM
      • Sumitani J
      • Mize T
      • Amarnath KK
      • Bayakly AR
      • et al.
      Public health impact of heat-related illness among migrant farmworkers.
      • Lam M
      • Krenz J
      • Palmández P
      • Negrete M
      • Perla M
      • Murphy-Robinson H
      • et al.
      Identification of barriers to the prevention and treatment of heat-related illness in Latino farmworkers using activity-oriented, participatory rural appraisal focus group methods.
      • Gronlund C.
      Racial and socioeconomic disparities in heat-related health effects and their mechanisms: a review.
      This study explored heat-related ED visits over time, which showed a disproportionate increase in presentation among minority populations compared with the white population.
      It is likely that other occupations that require physical exertion in an outdoor setting will be similarly susceptible to ED presentation with heat-related illness. Minorities are more likely to be of lower socioeconomic status and to live in densely populated areas—urban heat islands—with no access to air conditioning.
      • Jesdale BM
      • Morello-Frosch R
      • Cushing L
      The racial/ethnic distribution of heat risk-related land cover in relation to residential segregation.
      Urban heat islands trap hot air, making such areas more vulnerable to subtle changes in temperature. Chronic illnesses such as chronic heart and renal failure are associated with a higher risk of heat-related illness and significant morbidity and mortality compared with the risk among healthy individuals.
      • Basu R
      • Pearson D
      • Malig B
      • Broadwin R
      • Green R
      The effect of high ambient temperature on emergency room visits.
      The control of such chronic illness can be correlated to the existing disparity in health insurance and access to care.
      • Basu R
      • Pearson D
      • Malig B
      • Broadwin R
      • Green R
      The effect of high ambient temperature on emergency room visits.
      There are a number of limitations to this study. Data collection over the years and across counties may not be of uniform quality. This study cannot account for confounding factors such as migration of individuals outside or within California to hotter counties or changes in access to care.
      As extreme weather events become more common, the overall frequency of heat-related illness is likely to continue to rise, possibly exacerbating the increasing disparity suggested by the data. Further research is necessary to determine the cause of this growing disparity and the necessary measures to address it.

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        Vulnerability to extreme heat and climate change: is ethnicity a factor.
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        Recruitment, methods, and descriptive results of a physiologic assessment of Latino farmworkers: the California heat illness prevention study.
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        Public health impact of heat-related illness among migrant farmworkers.
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