Association of Temperature Thresholds with Heat Illness– and Cardiorespiratory-Related Emergency Visits during Summer Months in Alaska

Background: Recent record-breaking hot temperatures in Alaska have raised concerns about the potential human health implications of heat exposure among this unacclimated population. Objectives: We estimated cardiorespiratory morbidity associated with days above summer (June–August) heat index (HI, apparent temperature) thresholds in three major population centers (Anchorage, Fairbanks, and the Matanuska-Susitna Valley) for the years 2015–2019. Methods: We implemented time-stratified case–crossover analyses of emergency department (ED) visits for International Classification of Diseases, 10th Revision codes indicative of heat illness and major cardiorespiratory diagnostic codes using data from the Alaska Health Facilities Data Reporting Program. Using conditional logistic regression models, we tested maximum hourly HI temperature thresholds between 21.1°C (70°F) and 30°C (86°F) for a single day, 2 consecutive days, and the absolute number of previous consecutive days above the threshold, adjusting for the daily average concentration of particulate matter ≤2.5μg. Results: There were increased odds of ED visits for heat illness above a HI threshold as low as 21.1°C (70°F) [odds ratio (OR)=13.84; 95% confidence interval (CI): 4.05, 47.29], and this increased risk continued for up to 4 d (OR=2.43; 95% CI: 1.15, 5.10). Asthma and pneumonia were the only respiratory outcomes positively associated with the HI: ED visits for both were highest the day after a heat event (Asthma: HI>27°C(80°F) OR=1.18; 95% CI: 1.00, 1.39; Pneumonia: HI>28°C(82°F) OR=1.40; 95% CI: 1.06, 1.84). There was a decreased odds of bronchitis-related ED visits when the HI was above thresholds of 21.1–28°C (70–82°F) across all lag days. We found stronger effects for ischemia and myocardial infarction (MI) than for respiratory outcomes. Multiple days of warm weather were associated with an increased risk of health impacts. For each additional preceding day above a HI of 22°C (72°F), the odds of ED visits related to ischemia increased 6% (95% CI: 1%, 12%); for each additional preceding day above a HI of 21.1°C (70°F), the odds of ED visits related to MI increased 7% (95% CI: 1%, 14%). Discussion: This study demonstrates the importance of planning for extreme heat events and developing local guidance for heat warnings, even in areas with historically mild summertime climates. https://doi.org/10.1289/EHP11363


Table of Contents
Tables S1a-l. Threshold analyses at Lags 0-5, stratified by sex Table S1a. Threshold analyses at Lags 0-5, stratified by sex. Table S1b. Odds ratios and 95% confidence intervals for emergency department (ED) visits among females for heat index (HI) on lag day 1 above versus below the threshold from single-day lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019b. Table S1c. Odds ratios and 95% confidence intervals for emergency department (ED) visits among females for heat index (HI) on lag day 2 above versus below the threshold from single-day lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S1d. Odds ratios and 95% confidence intervals for emergency department (ED) visits among females for heat index (HI) on lag day 3 above versus below the threshold from single-day lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S1e. Odds ratios and 95% confidence intervals for emergency department (ED) visits among females for heat index (HI) on lag day 4 above versus below the threshold from single-day lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S1f. Odds ratios and 95% confidence intervals for emergency department (ED) visits among females for heat index (HI) on lag day 5 above versus below the threshold from single-day lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S1g. Odds ratios and 95% confidence intervals for emergency department (ED) visits among males for same-day heat index (HI) above versus below the threshold from single-day lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S1h. Odds ratios and 95% confidence intervals for emergency department (ED) visits among males for heat index (HI) on lag day 1 above versus below the threshold from single-day lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S1i. Odds ratios and 95% confidence intervals for emergency department (ED) visits among males for heat index (HI) on lag day 2 above versus below the threshold from single-day lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S1j. Odds ratios and 95% confidence intervals for emergency department (ED) visits among males for heat index (HI) on lag day 3 above versus below the threshold from single-day lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S1k. Odds ratios and 95% confidence intervals for emergency department (ED) visits among males for heat index (HI) on lag day 4 above versus below the threshold from single-day lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S1l. Odds ratios and 95% confidence intervals for emergency department (ED) visits among males for heat index (HI) on lag day 5 above versus below the threshold from single-day lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019.
Tables S2a-l. Threshold analyses at Lags 0-5, stratified by race. Table S2a. Odds ratios and 95% confidence intervals for emergency department (ED) visits among Alaskan Native people for same-day heat index (HI) above versus below the threshold from single-day lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S2b. Odds ratios and 95% confidence intervals for emergency department (ED) visits among Alaskan Native people for heat index (HI) on lag day 1 above versus below the threshold from single-day lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S2b. Odds ratios and 95% confidence intervals for emergency department (ED) visits among Alaskan Native people for heat index (HI) on lag day 1 above versus below the threshold from single-day lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S2c. Odds ratios and 95% confidence intervals fo emergency department (ED) visits among Alaskan Native people for heat index (HI) on lag day 2 above versus below the threshold from single-day lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S2d. Odds ratios and 95% confidence intervals for emergency department (ED) visits among Alaskan Native people for heat index (HI) on lag day 3 above versus below the threshold from single-day lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S2e. Odds ratios and 95% confidence intervals for emergency department (ED) visits among Alaskan Native people for heat index (HI) on lag day 4 above versus below the threshold from single-day lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S2f. Odds ratios and 95% confidence intervals for emergency department (ED) visits among Alaskan Native people for heat index (HI) on lag day 5 above versus below the threshold from single-day lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S2g. Odds ratios and 95% confidence intervals for emergency department (ED) visits among Non-Alaskan Native people for same-day heat index (HI) above versus below the threshold from single-day lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S2h. Odds ratios and 95% confidence intervals for emergency department (ED) visits among Non-Alaskan Native people for heat index (HI) on lag day 1 above versus below the threshold from single-day lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S2i. Odds ratios and 95% confidence intervals for emergency department (ED) visits among Non-Alaskan Native people for heat index (HI) on lag day 2 above versus below the threshold from single-day lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S2j. Odds ratios and 95% confidence intervals for emergency department (ED) visits among Non-Alaskan Native people for heat index (HI) on lag day 3 above versus below the threshold from single-day lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S2k. Odds ratios and 95% confidence intervals for emergency department (ED) visits among Non-Alaskan Native people for heat index (HI) on lag day 4 above versus below the threshold from single-day lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S2l. Odds ratios and 95% confidence intervals for emergency department (ED) visits among Non-Alaskan Native people for heat index (HI) on lag day 5 above versus below the threshold from single-day lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S3a. Odds ratios and 95% confidence intervals for emergency department (ED) visits among <15-year-olds for same-day heat index (HI) above versus below the threshold from singleday lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S3b. Odds ratios and 95% confidence intervals for emergency department (ED) visits among <15-year-olds for heat index (HI) on lag day 1 above versus below the threshold from single-day lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S3c. Odds ratios and 95% confidence intervals for emergency department (ED) visits among <15-year-olds for heat index (HI) on lag day 2 above versus below the threshold from single-day lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S3d. Odds ratios and 95% confidence intervals for emergency department (ED) visits among <15-year-olds for heat index (HI) on lag day 3 above versus below the threshold from single-day lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S3e. Odds ratios and 95% confidence intervals for emergency department (ED) visits among <15-year-olds for heat index (HI) on lag day 4 above versus below the threshold from single-day lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S3f. Odds ratios and 95% confidence intervals for emergency department (ED) visits among <15-year-olds for heat index (HI) on lag day 5 above versus below the threshold from single-day lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S3g. Odds ratios and 95% confidence intervals for emergency department (ED) visits among 15-65 year-olds for same-day heat index (HI) above versus below the threshold from single-day lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S3h. Odds ratios and 95% confidence intervals for emergency department (ED) visits among 15-65 year-olds for heat index (HI) on lag day 1 above versus below the threshold from single-day lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S3i. Odds ratios and 95% confidence intervals for emergency department (ED) visits among 15-65 year-olds for heat index (HI) on lag day 2 above versus below the threshold from single-day lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S3j. Odds ratios and 95% confidence intervals for emergency department (ED) visits among 15-65 year-olds for heat index (HI) on lag day 3 above versus below the threshold from single-day lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S3k. Odds ratios and 95% confidence intervals for emergency department (ED) visits among 15-65 year-olds for heat index (HI) on lag day 4 above versus below the threshold from single-day lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S3l. Odds ratios and 95% confidence intervals for emergency department (ED) visits among 15-65 year-olds for heat index (HI) on lag day 5 above versus below the threshold from single-day lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S3m. Odds ratios and 95% confidence intervals for emergency department (ED) visits among >65-year-olds for same-day heat index (HI) above versus below the threshold from singleday lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S3n. Odds ratios and 95% confidence intervals for ED emergency department (ED) visits among >65-year-olds for heat index (HI) on lag day 1 above versus below the threshold from single-day lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S3o. Odds ratios and 95% confidence intervals for emergency department (ED) visits among >65-year-olds for heat index (HI) on lag day 2 above versus below the threshold from single-day lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S3p. Odds ratios and 95% confidence intervals for emergency department (ED) visits among >65-year-olds for heat index (HI) on lag day 3 above versus below the threshold from single-day lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S3q. Odds ratios and 95% confidence intervals for emergency department (ED) visits among >65-year-olds for heat index (HI) on lag day 4 above versus below the threshold from single-day lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S3r. Odds ratios and 95% confidence intervals for emergency department (ED) visits among >65-year-olds for heat index (HI) on lag day 5 above versus below the threshold from single-day lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S4a. Odds ratios and 95% confidence intervals for emergency department (ED) visits on heatwave days versus non-heatwave days among females in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019.     Tables S5a-g. Ongoing heatwave analysis stratified by sex, race, and age Table S5a. Odds ratios and 95% confidence intervals for one additional previous day on which the observed heat index (HI) was above the indicated threshold among females in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S5b. Odds ratios and 95% confidence intervals for one additional previous day on which the observed heat index (HI) was above the indicated threshold among males in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S5c. Odds ratios and 95% confidence intervals for one additional previous day on which the observed heat index (HI) was above the indicated threshold among Alaska Native people in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S5d. Odds ratios and 95% confidence intervals for one additional previous day on which the observed heat index (HI) was above the indicated threshold among non-Alaska Native people in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S5e. Odds ratios and 95% confidence intervals for one additional previous day on which the observed heat index (HI) was above the indicated threshold among <15 year-olds in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S5f. Odds ratios and 95% confidence intervals for one additional previous day on which the observed heat index (HI) was above the indicated threshold among 15-65 year olds in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Table S5g. Odds ratios and 95% confidence intervals for one additional previous day on which the observed heat index (HI) was above the indicated threshold among >65 year-olds in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019.  Figure S2. Significant odds ratios (95% CI does not include the null) for asthma-related emergency department visits by demographic group on days above vs. below the Heat Index (HI) threshold, in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Conditional logistic regression models adjusted for daily PM2.5 concentration were used to estimate odds ratios. See Figure S1 for legend. Data for this figure can be found in Tables S1a-1,  Tables S2a-l, and Tables S3a-r. Figure S3. Significant odds ratios (95% CI does not include the null) for bronchitis-related emergency department visits by demographic group on days above vs. below the Heat Index (HI) threshold, in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Conditional logistic regression models adjusted for daily PM2.5 concentration were used to estimate odds ratios. See Figure S1 for legend. Data for this figure can be found in Tables S1a-1,  Tables S2a-l, and Tables S3a-r. Figure S4. Significant odds ratios (95% CI does not include the null) for COPD-related emergency department visits by demographic group on days above vs. below the Heat Index (HI) threshold, in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Conditional logistic regression models adjusted for daily PM2.5 concentration were used to estimate odds ratios. See Figure S1 for legend. Data for this figure can be found in Tables S1a-1,  Tables S2a-l, and Tables S3a-r. Figure S5. Significant odds ratios (95% CI does not include the null) for pneumonia-related emergency department visits by demographic group on days above vs. below the Heat Index (HI) threshold, in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Conditional logistic regression models adjusted for daily PM2.5 concentration were used to estimate odds ratios. See Figure S1 for legend. Data for this figure can be found in Tables S1a-1,  Tables S2a-l, and Tables S3a-r. Figure S6. Significant odds ratios (95% CI does not include the null) for arrythmia-related emergency department visits by demographic group on days above vs. below the Heat Index (HI) threshold, in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Conditional logistic regression models adjusted for daily PM2.5 concentration were used to estimate odds ratios. See Figure S1 for legend. Data for this figure can be found in Tables S1a-1,  Tables S2a-l, and Tables S3a-r. Figure S7. Significant odds ratios (95% CI does not include the null) for cerebrovascular-related emergency department visits by demographic group on days above vs. below the Heat Index (HI) threshold, in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Conditional logistic regression models adjusted for daily PM2.5 concentration were used to estimate odds ratios. See Figure S1 for legend. Data for this figure can be found in Tables S1a-1, Tables S2a-l, and Tables S3a-r. Figure S8. Significant odds ratios (95% CI does not include the null) for heart failure-related emergency department visits by demographic group on days above vs. below the Heat Index (HI) threshold, in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Conditional logistic regression models adjusted for daily PM2.5 concentration were used to estimate odds ratios. See Figure S1 for legend. Data for this figure can be found in Tables S1a-1,  Tables S2a-l, and Tables S3a-r. Figure S9. Significant odds ratios (95% CI does not include the null) for ischemia-related emergency department visits by demographic group on days above vs. below the Heat Index (HI) threshold, in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Conditional logistic regression models adjusted for daily PM2.5 concentration were used to estimate odds ratios. See Figure S1 for legend. Data for this figure can be found in Tables S1a-1,  Tables S2a-l, and Tables S3a-r. Figure S10. Significant odds ratios (95% CI does not include the null) for myocardial infarctionrelated emergency department visits by demographic group on days above vs. below the Heat Index (HI) threshold, in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Conditional logistic regression models adjusted for daily PM2.5 concentration were used to estimate odds ratios. See Figure S1 for legend. Data for this figure can be found in Tables S1a-1,  Tables S2a-l, and Tables S3a-r. Figure S11. Significant odds ratios (95% CI does not include the null) for heat illness-related emergency department visits by demographic group on days above vs. below the Heat Index (HI) threshold, in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019. Conditional logistic regression models adjusted for daily PM2.5 concentration were used to estimate odds ratios. See Figure S1 for legend. Data for this figure can be found in Tables S1a-1,  Tables S2a-l, and Tables S3a-r. Tables S1a-l -Threshold analyses at Lags 0-5, stratified by sex       Note: Conditional logistic regression models adjusted for daily PM 2.5 concentration were used to estimate odds ratios. Abbreviations: COPD, chronic obstructive pulmonary disease.   Note: Conditional logistic regression models adjusted for daily PM 2.5 concentration were used to estimate odds ratios. Abbreviations: COPD, chronic obstructive pulmonary disease. Table S1j. Odds ratios and 95% confidence intervals for emergency department (ED) visits among males for heat index (HI) on lag day 3 above versus below the threshold from single-day lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019    This footnote is to designate that only one ED visit related to the indicated health outcome occurred on an exposed day (i.e., a day during which the HI exceeded the indicated threshold) during the study period.              b This footnote is to designate that only one ED visit related to the indicated health outcome occurred two days after an exposure (i.e., a day during which the HI exceeded the indicated threshold) during the study period.

Number of cases
Note: Conditional logistic regression models adjusted for daily PM 2.5 concentration were used to estimate odds ratios. Abbreviations: COPD, chronic obstructive pulmonary disease.      Note: Conditional logistic regression models adjusted for daily PM 2.5 concentration were used to estimate odds ratios. Abbreviations: COPD, chronic obstructive pulmonary disease. Table S3i. Odds ratios and 95% confidence intervals for emergency department (ED) visits among 15-65 year-olds for heat index (HI) on lag day 2 above versus below the threshold from singleday lag models in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019    Note: Conditional logistic regression models adjusted for daily PM 2.5 concentration were used to estimate odds ratios. Abbreviations: COPD, chronic obstructive pulmonary disease.     Note: Conditional logistic regression models adjusted for daily PM 2.5 concentration were used to estimate odds ratios. Abbreviations: COPD, chronic obstructive pulmonary disease. Table S3r. Odds ratios and 95% confidence intervals for emergency department (ED) visits among >65-year-olds for heat index (HI) on lag day 5 above versus below the threshold from singleday lag models in Anchorage, Fairbanks, andthe Matanuska-Susitna Valley, Alaska, 2015-2019 Tables S4a-g -Acute heatwave analysis stratified by sex, race, and age  Table S4a. Odds ratios and 95% confidence intervals for emergency department (ED) visits on heatwave days versus non-heatwave days among females in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019 This footnote is to designate that only one ED visit related to the indicated health outcome occurred on an exposed day (i.e., an acute heatwave day as defined above) during the study period.

Number of cases
Note: For the acute heatwave analysis, the results of which are reported in this table, a heatwave day was defined as a day on which the observed heat index (HI) was above the indicated threshold as was the HI on the previous day. Days with a HI below the threshold and/or those that were preceded by a daily HI below the threshold were considered non-heatwave days. Conditional logistic regression models adjusted for daily PM 2.5 concentration were used to estimate odds ratios. Abbreviations: COPD, chronic obstructive pulmonary disease.  This footnote is to designate that only one ED visit related to the indicated health outcome occurred on an exposed day (i.e., an acute heatwave day as defined above) during the study period.

Number of cases
Note: For the acute heatwave analysis, the results of which are reported in this table, a heatwave day was defined as a day on which the observed heat index (HI) was above the indicated threshold as was the HI on the previous day. Days with a HI below the threshold and/or those that were preceded by a daily HI below the threshold were considered non-heatwave days. Conditional logistic regression models adjusted for daily PM 2.5 concentration were used to estimate odds ratios. Abbreviations: COPD, chronic obstructive pulmonary disease.  Table S4c. Odds ratios and 95% confidence intervals for emergency department (ED) visits on heatwave days versus non-heatwave days among Alaska Native people in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019 This footnote is to designate that only one ED visit related to the indicated health outcome occurred on an exposed day (i.e., an acute heatwave day as defined above) during the study period.

Number of cases
Note: For the acute heatwave analysis, the results of which are reported in this table, a heatwave day was defined as a day on which the observed heat index (HI) was above the indicated threshold as was the HI on the previous day. Days with a HI below the threshold and/or those that were preceded by a daily HI below the threshold were considered non-heatwave days. Conditional logistic regression models adjusted for daily PM 2.5 concentration were used to estimate odds ratios. Abbreviations: COPD, chronic obstructive pulmonary disease.  This footnote is to designate that only one ED visit related to the indicated health outcome occurred on an exposed day (i.e., an acute heatwave day as defined above) during the study period.

Number of cases
Note: For the acute heatwave analysis, the results of which are reported in this table, a heatwave day was defined as a day on which the observed heat index (HI) was above the indicated threshold as was the HI on the previous day. Days with a HI below the threshold and/or those that were preceded by a daily HI below the threshold were considered non-heatwave days. Conditional logistic regression models adjusted for daily PM 2.5 concentration were used to estimate odds ratios. Abbreviations: COPD, chronic obstructive pulmonary disease.  This footnote is to designate that only one ED visit related to the indicated health outcome occurred on an exposed day (i.e., an acute heatwave day as defined above) during the study period.

Number of cases
Note: For the acute heatwave analysis, the results of which are reported in this table, a heatwave day was defined as a day on which the observed heat index (HI) was above the indicated threshold as was the HI on the previous day. Days with a HI below the threshold and/or those that were preceded by a daily HI below the threshold were considered non-heatwave days. Conditional logistic regression models adjusted for daily PM 2.5 concentration were used to estimate odds ratios. Abbreviations: COPD, chronic obstructive pulmonary disease.  This footnote is to designate that only one ED visit related to the indicated health outcome occurred on an exposed day (i.e., an acute heatwave day as defined above) during the study period.

Number of cases
Note: For the acute heatwave analysis, the results of which are reported in this table, a heatwave day was defined as a day on which the observed heat index (HI) was above the indicated threshold as was the HI on the previous day. Days with a HI below the threshold and/or those that were preceded by a daily HI below the threshold were considered non-heatwave days. Conditional logistic regression models adjusted for daily PM 2.5 concentration were used to estimate odds ratios. Abbreviations: COPD, chronic obstructive pulmonary disease.  Table S4g. Odds ratios and 95% confidence intervals for emergency department (ED) visits on heatwave days versus non-heatwave days among >65-year-olds in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019 This footnote is to designate that only one ED visit related to the indicated health outcome occurred on an exposed day (i.e., an acute heatwave day as defined above) during the study period.

Number of cases
Note: For the acute heatwave analysis, the results of which are reported in this table, a heatwave day was defined as a day on which the observed heat index (HI) was above the indicated threshold as was the HI on the previous day. Days with a HI below the threshold and/or those that were preceded by a daily HI below the threshold were considered non-heatwave days. Conditional logistic regression models adjusted for daily PM 2.5 concentration were used to estimate odds ratios. Abbreviations: COPD, chronic obstructive pulmonary disease.
Tables S5a-g -Ongoing heatwave analysis stratified by sex, race, and age  Table S5a. Odds ratios and 95% confidence intervals for one additional previous day on which the observed heat index (HI) was above the indicated threshold among females in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019 Note: For the ongoing heatwave analysis, the results of which are reported in this table, the effect of prolonged elevated HI was estimated via a linear variable in the model that represented the number of previous consecutive days on which the observed HI was above the relevant threshold. An indicator variable was also included to control for same-day elevated HI. As with the threshold analysis, a value of `1` indicated that the same-day HI was above the relevant threshold and a value of `0` indicated that the same-day HI was below the relevant threshold. Conditional logistic regression models adjusted for daily PM 2.5 concentration were used to estimate odds ratios. Abbreviations: COPD, chronic obstructive pulmonary disease.  Table S5b. Odds ratios and 95% confidence intervals for one additional previous day on which the observed heat index (HI) was above the indicated threshold among males in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015-2019

Number of cases
Note: For the ongoing heatwave analysis, the results of which are reported in this table, the effect of prolonged elevated HI was estimated via a linear variable in the model that represented the number of previous consecutive days on which the observed HI was above the relevant threshold. An indicator variable was also included to control for same-day elevated HI. As with the threshold analysis, a value of `1` indicated that the same-day HI was above the relevant threshold and a value of `0` indicated that the same-day HI was below the relevant threshold. Conditional logistic regression models adjusted for daily PM 2.5 concentration were used to estimate odds ratios. Abbreviations: COPD, chronic obstructive pulmonary disease.