Table 12.

ORs and 95% CIs for ED visits associated with a maximum daily HI above vs. below the indicated threshold on the indicated lag day for models in which an interaction term between ${\mathrm{PM}}_{2.5}$ and elevated HI was significant in Anchorage, Fairbanks, and the Matanuska-Susitna Valley, Alaska, 2015–2019.

Reason for ED visit	Lag day	HI threshold	Original modela	Interaction modelb
				${5\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$	${10\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$	${20\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$	${35\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$
Asthma	1	84	1.10 (0.75, 1.62)	1.59 (0.98, 2.60)	1.50 (0.95, 2.37)	1.34 (0.90, 2.00)	1.13 (0.77, 1.64)
Asthma	2	84	0.91 (0.60, 1.39)	1.31 (0.79, 2.18)	1.24 (0.77, 2.00)	1.12 (0.73, 1.73)	0.96 (0.63, 1.44)
Asthma	5	70	0.92 (0.85, 1.00)	0.93 (0.86, 1.01)	0.90 (0.82, 0.98)c	0.83 (0.74, 0.94)c	0.74 (0.60, 0.92)c
Asthma	5	72	0.90 (0.82, 0.98)c	0.91 (0.84, 1.00)	0.88 (0.81, 0.96)c	0.82 (0.72, 0.93)c	0.74 (0.59, 0.91)c
Asthma	5	74	0.94 (0.86, 1.04)	0.96 (0.87, 1.07)	0.93 (0.84, 1.02)	0.86 (0.75, 0.97)c	0.76 (0.61, 0.94)c
Bronchitis	2	82	0.78 (0.55, 1.11)	0.64 (0.42, 0.96)c	0.67 (0.46, 1.00)c	0.75 (0.52, 1.09)	0.89 (0.61, 1.31)
Bronchitis	2	86	0.91 (0.33, 2.50)	—	—	—	—
Bronchitis	5	82	0.92 (0.66, 1.29)	0.77 (0.52, 1.14)	0.81 (0.56, 1.17)c	0.89 (0.62, 1.27)	1.03 (0.71, 1.50)
Bronchitis	5	84	1.10 (0.63, 1.92)	0.77 (0.39, 1.52)	0.82 (0.43, 1.58)c	0.93 (0.50, 1.72)	1.12 (0.62, 2.01)
COPD	2	80	0.76 (0.60, 0.96)c	0.68 (0.53, 0.89)c	0.72 (0.56, 0.92)c	0.80 (0.62, 1.03)	0.93 (0.68, 1.28)
COPD	3	74	0.83 (0.74, 0.93)c	0.81 (0.72, 0.92)c	0.86 (0.76, 0.97)c	0.96 (0.80, 1.16)	1.13 (0.82, 1.57)
COPD	3	76	0.83 (0.73, 0.96)c	0.81 (0.70, 0.93)c	0.86 (0.74, 0.99)c	0.96 (0.79, 1.16)	1.14 (0.82, 1.58)
COPD	3	80	0.76 (0.60, 0.97)c	0.69 (0.53, 0.89)c	0.72 (0.56, 0.93)c	0.80 (0.62, 1.02)	0.92 (0.68, 1.26)
COPD	3	84	0.62 (0.34, 1.15)	0.41 (0.18, 0.90)c	0.43 (0.20, 0.93)c	0.48 (0.23, 1.00)c	0.57 (0.29, 1.13)
COPD	5	70	0.90 (0.82, 0.99)c	0.91 (0.83, 1.00)	0.87 (0.78, 0.96)c	0.78 (0.67, 0.91)c	0.67 (0.52, 0.88)c
COPD	5	72	0.86 (0.78, 0.96)c	0.88 (0.79, 0.97)c	0.83 (0.75, 0.93)c	0.75 (0.65, 0.88)c	0.65 (0.50, 0.84)c
COPD	5	74	0.86 (0.77, 0.97)c	0.88 (0.79, 0.99)c	0.84 (0.75, 0.94)c	0.76 (0.65, 0.89)c	0.65 (0.50, 0.85)c
COPD	5	76	0.81 (0.71, 0.93)c	0.84 (0.73, 0.96)c	0.80 (0.70, 0.92)c	0.73 (0.62, 0.86)c	0.64 (0.49, 0.83)c
COPD	5	78	0.77 (0.65, 0.91)c	0.81 (0.68, 0.96)c	0.77 (0.65, 0.91)c	0.69 (0.58, 0.83)c	0.59 (0.45, 0.78)c
Heart failure	2	84	0.29 (0.04, 2.14)	—	—	—	—
Heart failure	3	86	1.10 (0.14, 8.60)	—	—	—	—
Heat illness	3	82	1.05 (0.22, 4.97)	32.77 (0.72, 1,497.60)	4.10 (0.73, 23.05)	0.06 (0.00, 23.79)	—
Ischemic	2	82	0.94 (0.36, 2.50)	3.21 (0.85, 12.16)	1.95 (0.69, 5.53)	0.72 (0.21, 2.50)	0.16 (0.01, 2.21)
Ischemic	5	80	1.37 (0.77, 2.44)	1.03 (0.54, 1.98)	1.25 (0.66, 2.36)	1.81 (0.84, 3.91)	3.18 (0.97, 10.49)
Myocardial infarction	0	70	1.53 (0.93, 2.49)	1.76 (0.97, 3.19)	3.00 (0.98, 9.18)	8.69 (0.76, 99.82)	42.84 (0.47, 3,881.40)
Pneumonia	1	70	0.82 (0.66, 1.02)	0.89 (0.81, 0.98)c	0.94 (0.85, 1.05)	1.06 (0.89, 1.26)	1.26 (0.93, 1.71)
Pneumonia	1	72	0.82 (0.65, 1.03)	0.88 (0.79, 0.98)c	0.94 (0.84, 1.05)	1.06 (0.89, 1.25)	1.26 (0.94, 1.71)
Pneumonia	1	74	0.88 (0.69, 1.14)	0.88 (0.78, 1.00)c	0.94 (0.83, 1.06)	1.05 (0.89, 1.25)	1.26 (0.93, 1.69)
Pneumonia	1	76	0.85 (0.64, 1.14)	0.93 (0.81, 1.07)	0.98 (0.85, 1.12)	1.08 (0.90, 1.29)	1.24 (0.93, 1.67)
Pneumonia	1	80	0.83 (0.51, 1.37)	1.11 (0.88, 1.39)	1.18 (0.95, 1.46)	1.33 (1.07, 1.66)c	1.60 (1.18, 2.15)c

Note: Conditional logistic regression models were used to estimate ORs. —, Model did not converge due to limited sample size; the model is nonetheless listed to indicate that the interaction term was significant for the relevant outcome, threshold, and lag day; CI, confidence interval; COPD, chronic obstructive pulmonary disease; ED, emergency department; HI, heat index; OR, odds ratio; ${\mathrm{PM}}_{2.5}$, particulate matter with aerodynamic diameter $\le 2.5\mathrm{\mu }\mathrm{m}$.

^a Reported ORs from the original model can be interpreted as the odds of an ED visit when the HI on the given lag day is above vs. below the given threshold, while controlling for daily mean ${\mathrm{PM}}_{2.5}$ concentration.

^b Reported ORs from the model that included an interaction between the indicator variable for HI above vs. below the threshold and daily mean ${\mathrm{PM}}_{2.5}$ concentration can be interpreted as the odds of an ED visit when the HI on the given lag day is above vs. below the given threshold and the ${\mathrm{PM}}_{2.5}$ concentration on the given lag day is 5, 10, 20, or $35{\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$.

^c 95% CI does not include the null.