Abstract
This study used a health care claims data set of enrollees in commercial and Medicare Advantage insurance plans to assess the association between the June 2021 heat wave and the rates of emergency department visits in Portland, Oregon, and Seattle, Washington.
Heat waves are becoming more frequent and severe, with pronounced effects on human health.1 In late June 2021, temperatures in the US Pacific Northwest reached record highs, with reported daily maximums of 46.6 °C in Portland, Oregon, and 42.0 °C in Seattle, Washington.2 The adverse health effects associated with this heat wave have only been partially quantified.3
Characterization of heat-related morbidity is useful for climate action planning, especially in areas not used to elevated summertime temperatures. We leveraged a health care claims data set of individuals enrolled in commercial and Medicare Advantage insurance plans to assess the association between the June 2021 heat wave and rates of emergency department (ED) visits in Portland and Seattle.
Methods
We obtained deidentified ED claims between January 1, 2021, and December 31, 2021, among enrollees of any age living in Portland and Seattle (selected counties appear in eTable 1 in Supplement 1) from the Optum Labs Data Warehouse.4 Claims related to heat exposure were those with a subset of standard International Statistical Classification of Diseases and Related Health Problems, Tenth Revision (ICD-10) diagnostic codes (eTable 2 in Supplement 1). The institutional review board at the Boston University Medical Campus approved this study.
Temperatures recorded from 2018 to 2021 at National Weather Service monitoring stations in each area were used to identify the heat wave periods, which were defined as 2 or more consecutive days with daily maximum temperature exceeding the 99th percentile of daily maximums of collected data (eTable 3 in Supplement 1). We used 2 reference periods consisting of the same days of the week as the 2021 heat wave, one occurring 1 week before the heat wave and one occurring 1 week after the heat wave. We assessed the effect of the heat wave on ED visits relative to the period before the heat wave. We used the period after the heat wave to assess whether the change in ED visits persisted after the heat wave ended.
We present incidence rates in ED visits per 100 000 enrollees and incidence rate ratios (IRRs) with 2-sided 95% CIs. We used R version 4.1.2 (R Foundation for Statistical Computing) and a threshold for statistical significance of P < .05 for the IRRs (eTable 4 in Supplement 1).5,6
Results
The heat wave days were June 26, 2021, to June 29, 2021. In Portland and Seattle, the rates of all-cause ED visits were not statistically significantly different during the heat wave period and before the heat wave period (Table).
Table. All-Cause and Heat-Related Emergency Department (ED) Visits and Incidence Rates Among Individuals Enrolled in Commercial and Medicare Advantage Insurance Plans in Portland, Oregon, and Seattle, Washington, During June and July 2021.
| No. of enrollees or ED visits | Incidence rate for ED visits per 100 000 enrollees | During heat wave (index) vs before heat wave (reference) | After heat wave (index) vs before heat wave (reference) | |||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Before heat wave (June 19-22) | During heat wave (June 26-29) | After heat wave (July 3-6) | Before heat wave (June 19-22) | During heat wave (June 26-29) | After heat wave (July 3-6) | IRR (95% CI) | P value | IRR (95% CI) | P value | |
| Portland, Oregon | ||||||||||
| Mean daily enrollees | 144 144 | 144 248 | 142 885 | |||||||
| All-cause ED visit | 288 | 275 | 326 | 200 | 191 | 228 | 0.95 (0.81-1.13) | .58 | 1.14 (0.97-1.34) | .10 |
| ED visit with any heat-related ICD-10 codea | 38 | 46 | 40 | 26 | 32 | 28 | 1.21 (0.79-1.86) | .38 | 1.06 (0.68-1.66) | .79 |
| ED visit with ICD-10 code related to fluid depletionb | 38 | 39 | 40 | 26 | 27 | 28 | 1.03 (0.66-1.60) | .91 | 1.06 (0.68-1.66) | .79 |
| ED visit with ICD-10 code related to heat exposurec | 0 | 12 | 0 | 0 | 8 | 0 | 16.80 (2.78-∞) | <.001 | NA (0-∞) | NA |
| Seattle, Washington | ||||||||||
| Mean daily enrollees | 158 492 | 158 642 | 158 856 | |||||||
| All-cause ED visit | 334 | 341 | 338 | 211 | 215 | 213 | 1.02 (0.88-1.19) | .80 | 1.01 (0.87-1.17) | .90 |
| ED visit with any heat-related ICD-10 codea | 28 | 62 | 32 | 18 | 39 | 20 | 2.21 (1.42-3.46) | <.001 | 1.14 (0.69-1.89) | .61 |
| ED visit with ICD-10 code related to fluid depletionb | 27 | 50 | 32 | 17 | 32 | 20 | 1.85 (1.16-2.95) | .01 | 1.18 (0.71-1.97) | .52 |
| ED visit with ICD-10 code related to heat exposurec | <11d | 16 | 0 | <7d | 10 | 0 | 9.33 (2.48-670.33) | <.001 | NA (0-38.9) | .50 |
Abbreviations: ICD-10, International Statistical Classification of Diseases and Related Health Problems, Tenth Revision; IRR, incidence rate ratio; NA, not applicable.
Code E86 (volume depletion), E87 (electrolyte imbalance), T67 (effects of heat and light), or X30 (exposure to excessive heat).
Code E86 (volume depletion) or E87 (electrolyte imbalance).
Code T67 (effects of heat and light) or X30 (exposure to excessive heat).
Value used to maintain deidentification.
However, in both Portland and Seattle, there was a significant increase in the rate of ED visits with claims containing ICD-10 codes for effects of heat and light (T67) or exposure to excessive heat (X30). In Portland, the incidence rate increased from 0 ED visits per 100 000 enrollees before the heat wave to 8 ED visits per 100 000 enrollees during the heat wave (IRR, 16.8 [95% CI, 2.78-∞]). In Seattle, the incidence rate increased from less than 7 ED visits per 100 000 enrollees before the heat wave to 10 ED visits per 100 000 enrollees during the heat wave (IRR, 9.33 [95% CI, 2.48-670.33]).
The number of claims with ICD-10 codes related to volume depletion (E86) and electrolyte imbalance (E87) significantly increased in Seattle during the heat wave compared with the period before the heat wave; the IR increased from 17 to 32 ED visits per 100 000 enrollees (IRR, 1.85 [95% CI, 1.16-2.95]).
In both Portland and Seattle, the rates of all-cause and heat-related ED visits during the period after the heat wave were not statistically significantly different from the rates before the heat wave.
Discussion
Among individuals enrolled in commercial and Medicare Advantage insurance plans, the June 2021 heat wave was associated with increased rates of heat-related ED visits, including visits directly attributed to heat exposure in Portland and Seattle and volume or electrolyte depletion in Seattle; ED visit levels returned to baseline within 1 week after the heat wave ended. These results are broadly consistent with previous literature indicating significant health risks posed by extreme heat,1,3 but contribute novel estimates of acute associations.
Study limitations include the restriction to a single heat wave in 2 metropolitan areas in the continental US, the small absolute number of events and wide 95% CIs, and the inability to study mortality using this data set. The study included only individuals enrolled in commercial and Medicare Advantage insurance plans. Heat may pose an even larger risk to individuals without health insurance.
Section Editors: Jody W. Zylke, MD, Deputy Editor; Kristin Walter, MD, Senior Editor.
eTable 1. Counties included in each area
eTable 2. International Statistical Classification of Diseases and Related Health Problems, Tenth Revision (ICD-10) diagnosis code used for heat-related illness
eTable 3. Daily maximum ambient temperature data from NWS weather monitoring stations in Seattle and Portland over the period 2018 to 2021
eTable 4. Calculation of incidence rate ratios for case numbers greater than 5
eMethods
Data Sharing Statement
References
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
eTable 1. Counties included in each area
eTable 2. International Statistical Classification of Diseases and Related Health Problems, Tenth Revision (ICD-10) diagnosis code used for heat-related illness
eTable 3. Daily maximum ambient temperature data from NWS weather monitoring stations in Seattle and Portland over the period 2018 to 2021
eTable 4. Calculation of incidence rate ratios for case numbers greater than 5
eMethods
Data Sharing Statement