A longitudinal ecological study of seasonal influenza deaths in relation to climate conditions in the United States from 1999 through 2011

Figures & data

Table 1. A demographic summary of the populations examined from 1999 through 2011.

Characteristic Examined	Influenza Deaths^a ICD-10 codes: J09, J10, J11	Overall Population^a	p-value^b
Gender			< 0.0001
Males	7,049 (41.54%)	1,874,617,892 (49.11%)
Females	9,920 (58.46%)	1,942,260,623 (50.89%)
Race^c			< 0.0001
Hispanic or Latino	1,224 (7.23%)	558,225,099 (14.62%)
Black or African American	1,048 (6.19%)	484,357,169 (12.69%)
White	14,210 (83.96%)	2,574,823,166 (67.46%)
Asian or Pacific Islander	285 (1.68%)	169,073,816 (4.43%)
American Indian or Alaska Native	159 (0.94%)	30,399,265 (0.8%)
Census Division			< 0.0001
Division 1: new England (CT, RI, MA, VT, NH, ME)	1,018 (6%)	184,735,107 (4.84%)
Division 2: Middle Atlantic (NY, PA, NJ)	1,683 (9.92%)	523,595,585 (13.72%)
Division 3: East North Central (WI, IL, IN, MI, OH)	3,128 (18.43%)	596,408,598 (15.63%)
Division 4: West North Central (ND, SD, NE, KS, MN, IA, MO)	2,499 (14.73%)	258,120,646 (6.76%)
Division 5: South Atlantic (WV, MD, DE, DC, VA, NC, SC, GA, FL)	2,516 (14.83%)	728,208,137 (19.08%)
Division 6: East South Central (KY, TN, MS, AL)	1,022 (6.02%)	230,170,336 (6.03%)
Division 7: West South Central (TX, OK, AR, LA)	1,593 (9.39%)	439,868,805 (11.52%)
Division 8: Mountain (NV, ID, UT, AZ, NM, CO, WY, MT)	1,427 (8.41%)	262,578,804 (6.88%)
Division 9: Pacific (WA, OR, CA)	2,083 (12.27%)	593,292,497 (15.54%)
2006 Urbanization			< 0.0001
Large Central Metro	3,360 (19.80%)	1,134,798,488 (29.73%)
Large Fringe Metro	2,847 (16.78%)	924,688,394 (24.23%)
Medium Metro	3,542 (20.87%)	750,229,439 (19.66%)
Small Metro	2,017 (11.89%)	365,860,187 (9.58%)
Micropolitan (non-metro)	2,670 (15.73%)	390,175,673 (10.22%)
Noncore (non-metro)	2,533 (14.93%)	251,126,334 (6.58%)

^a The values were derived by adding the values for each year examined to calculate the cumulative numbers presented in the table.

^b Determined using the χ² statistic.

^c A total of 16,969 influenza deaths were identified, but 43 did not state Hispanic origin or not and were excluded from the table.

Table 2. A summary of the mean climate exposure for each census division from 1999 through 2011.

Census Division	Mean Daily Sunlight in KJ/m^2 (# of obs) [range]	Mean Daily Max Air Temperature in °C (# of obs) [range]	Mean Daily Min Air Temperature in °C (# of obs) [range]	Mean Daily Precipitation in mm (# of obs) [range]
Division 1: new England (CT, RI, MA, VT, NH, ME)	14,174.96 (5,787,812) [1,095.30 to 33,875.30]	10.97 (5,787,812) [−29.56 to 38.28]	3.07 (5,787,812) [−39.22 to 26.33]	3.34 (5,787,812) [0.00 to 215.00]
Division 2: Middle Atlantic (NY, PA, NJ)	14,307.90 (8,612,872) [1,151.50 to 33,935.20]	13.20 (8,612,872) [−26.39 to 40.44]	4.98 (8,612,872) [−34.94 to 27.33]	3.14 (8,612,872) [0.00 to 212.90]
Division 3: East North Central (WI, IL, IN, MI, OH)	14,771.15 (21,309,024) [940.50 to 33,921.90]	14.31 (21,309,024) [−24.28 to 45.94]	5.31 (21,309,024) [−37.50 to 29.28]	2.64 (21,309,024) [0.00 to 220.40]
Division 4: West North Central (ND, SD, NE, KS, MN, IA, MO)	15,295.92 (44,802,128) [921.80 to 32,297.50]	15.28 (44,802,128) [−30.78 to 48.22]	4.61 (44,802,128) [−41.44 to 30.61]	1.95 (44,802,128) [0.00 to 244.40]
Division 5: South Atlantic (WV, MD, DE, DC, VA, NC, SC, GA, FL)	17,151.67 (20,995,656) [1,562.80 to 39,461.40]	21.76 (20,995,656) [−17.56 to 42.94]	12.06 (20,995,656) [−23.72 to 30.17]	3.24 (20,995,656) [0.00 to 274.60]
Division 6: East South Central (KY, TN, MS, AL)	16,667.88 (14,039,836) [1,511.20 to 35,355.40]	21.69 (14,039,836) [−13.28 to 45.67]	11.43 (14,039,836) [−28.28 to 32.17]	3.57 (14,039,836) [0.00 to 257.50]
Division 7: West South Central (TX, OK, AR, LA)	18,113.12 (32,727,964) [1,629.00 to 36,062.70]	25.12 (32,727,964) [−15.11 to 47.61]	13.20 (32,727,964) [−22.94 to 32.50]	2.37 (32,727,964) [0.00 to 277.80]
Division 8: Mountain (NV, ID, UT, AZ, NM, CO, WY, MT)	17,299.97 (72,592,172) [993.40 to 33,959.80]	15.10 (72,592,172) [−32.17 to 49.61]	5.05 (72,592,172) [−39.06 to 37.28]	1.07 (72,592,172) [0.00 to 214.60]
Division 9: Pacific (WA, OR, CA)	17,371.03 (27,519,408) [963.60 to 38,703.70]	16.72 (27,519,408) [−24.06 to 51.22]	6.88 (27,519,408) [−31.56 to 37.67]	1.93 (27,519,408) [0.00 to 521.60]
Total	16,612.30 (248,386,872) [921.80 to 39,461.40]	17.34 (248,386,872) [−32.17 to 51.22]	7.17 (248,386,872) [−41.44 to 37.67]	2.08 (248,386,872) [0.00 to 521.60]

Table 3. A summary of the correlation^a between climate exposure variables and influenza death rate.

Breakdown of Data Examined (# of obs)	Mean Daily Sunlight in KJ/m^2 vs Influenza Death Rate	Mean Daily Max Air Temperature in °C vs Influenza Death Rate	Mean Daily Min Air Temperature in °C vs Influenza Death Rate	Mean Daily Precipitation in mm vs Influenza Death Rate
Census Division (n = 9)	Rho = −0.25 95% CI = −0.784 to 0.497 p = 0.4933	Rho = −0.317 95% CI = −0.810 to 0.44 p = 0.3853	Rho = −0.55 95% CI = −0.889 to 0.18 p = 0.1206	Rho = −0.167 95% CI = −0.748 to 0.559 p = 0.6436
Census Division by Year (n = 117)	Rho = −0.203 95% CI = −0.371 to −0.022 p = 0.0285	Rho = −0.197 95% CI = −0.366 to −0.0164 p = 0.0331	Rho = −0.333 95% CI = −0.485 to −0.161 p = 0.0003	Rho = 0.0143 95% CI = −0.195 to 0.168 p = 0.8783
State (n = 49)	Rho = −0.498 95% CI = −0.683 to −0.252 p = 0.0003	Rho = −0.566 95% CI = −0.731 to −0.339 p < 0.001	Rho = −0.666 95% CI = −0.798 to −0.473 p < 0.0001	Rho = −0.336 95% CI = −0.564 to −0.60 p = 0.0188
State by Year (n = 422)	Rho = −0.314 95% CI = −0.398 to −0.226	Rho = −0.402 95% CI = −0.479 to −0.319	Rho = −0.48 95% CI = −0.55 to −0.403	Rho = −0.193 95% CI = −0.283 to −0.1
	p < 0.0001	p < 0.0001	p < 0.0001	p < 0.0001

Note: Bold-Italics results are statistically significant.

^a The Spearman’s rank correlation statistic was employed

Table 4. A summary of the correlation^a between climate exposure variables and influenza death rate broken down by state from 1999 through 2011 for different demographic groups.

Breakdown of Data Examined (# of obs)	Mean Daily Sunlight in KJ/m^b vs Influenza Death Rate	Mean Daily Max Air Temperature in °C vs Influenza Death Rate	Mean Daily Min Air Temperature in °C vs Influenza Death Rate	Mean Daily Precipitation in mm vs Influenza Death Rate
Gender
Males (n = 48)	Rho = −0.383 95% CI = −0.602 to −0.111 p = 0.0076	Rho = −0.504 95% CI = −0.689 to −0.257 p = 0.0003	Rho = −0.613 95% CI = −0.764 to −0.398 p < 0.0001	Rho = −0.440 95% CI = −0.644 to −0.178 p = 0.0019
Females (n = 49)	Rho = −0.543 95% CI = −0.715 to −0.308 p < 0.0001	Rho = −0.585 95% CI = −0.744 to −0.364 p < 0.0001	Rho = −0.677 95% CI = −0.805 to −0.489 p < 0.0001	Rho = −0.292 95% CI = −0.529 to −0.011 p = 0.0424
Race^b
Hispanic or Latino (n = 19)	Rho = 0.453 95% CI = −0.002 to 0.752 p = 0.0523	Rho = 0.08 95% CI = −0.388 to 0.515 p = 0.7427	Rho = −0.051 95% CI = −0.494 to 0.413 p = 0.8372	Rho = −0.802 95% CI = −0.921 to −0.547 p < 0.0001
Black or African American (n = 28)	Rho = −0.153 95% CI = −0.498 to 0.233 p = 0.4345	Rho = −0.203 95% CI = −0.535 to 0.184 p = 0.3	Rho = −0.228 95% CI = −0.554 to 0.158 p = 0.2417	Rho = −0.337 95% CI = −0.631 to 0.041 p = 0.0793
White (n = 48)	Rho = −0.515 95% CI = −0.697 to −0.27 p = 0.0002	Rho = −0.521 95% CI = −0.701 to −0.278 p = 0.0002	Rho = −0.622 95% CI = −0.77 to −0.41 p < 0.00001	Rho = −0.298 95% CI = −0.537 to −0.015 p = 0.0399
2006 Urbanization
Large Central Metro (n = 31)	Rho = −0.160 95% CI = −0.487 to 0.206 p = 0.3884	Rho = −0.352 95% CI = −0.628 to 0.003 p = 0.0528	Rho = −0.396 95% CI = −0.658 to −0.048 p = 0.0284	Rho = −0.195 95% CI = −0.514 to 0.171 p = 0.2914
Large Fringe Metro (n = 32)	Rho = −0.356 95% CI = −0.627 to −0.009 p = 0.046	Rho = −0.417 95% CI = −0.669 to −0.080 p = 0.0183	Rho = −0.458 95% CI = −0.696 to −0.130 p = 0.009	Rho = −0.147 95% CI = −0.417 to 0.213 p = 0.4217
Medium Metro (n = 40)	Rho = −0.516 95% CI = −0.713 to −0.244 p = 0.0008	Rho = −0.457 95% CI = −0.673 to −0.17 p = 0.0033	Rho = −0.512 95% CI = −0.711 to 0.239 p = 0.0008	Rho = −0.249 95% CI = −0.52 to 0.068 p = 0.1218
Small Metro (n = 39)	Rho = −0.632 95% CI = −0.790 to −0.4 p < 0.00001	Rho = −0.759 95% CI = −0.867 to −0.528 p < 0.0001	Rho = −0.792 95% CI = −0.886 to −0.6.35 p < 0.0001	Rho = −0.407 95% CI = −0.640 to −0.105 p = 0.0106
Micropolitan (non-metro) (n = 43)	Rho = −0.627 95% CI = −0.780 to −0.402 p < 0.0001	Rho = −0.682 95% CI = −0.815 to −0.480 p < 0.0001	Rho = −0.748 95% CI = −0.856 to −0.578 p < 0.0001	Rho = −0.411 95% CI = −0.633 to −0.126 p = 0.0065
Noncore (non-metro) (n = 41)	Rho = −0.374 95% CI = −0.611 to −0.075 p = 0.0165	Rho = −0.586 95% CI = −0.757 to −0.340 p < 0.00001	Rho = −0.658 95% CI = −0.803 to −0.44 p < 0.0001	Rho = −0.560 95% CI = −0.740 to −0.305 p = 0.0002

Note: Bold-Italics results are statistically significant.

^a The Spearman’s rank correlation statistic was employed.

^b Analyses by Asian or Pacific Islander and American Indian or Alaska Native were not possible because there were too few influenza deaths by state. A total of 16,969 influenza deaths were identified, but 43 did not state Hispanic origin or not and were excluded from the table.