Table 1.
Demographic and Clinical Characteristics, Lifestyle Risk Factors, and Clinical Course of Hospitalization Among 5614 Cases, Overall and by Vaccination Status During the 2012–2013 Influenza Season
| Characteristic | Overall (n = 5614) | Vaccinated (n = 3101) | Unvaccinated (n = 2513) | P Valuea |
|---|---|---|---|---|
| Female sex | 2952 (53) | 1598 (52) | 1354 (54) | .08 |
| Age group, y | ||||
| 50–64 | 1638 (29) | 667 (22) | 971 (39) | <.001 |
| 65–74 | 1296 (23) | 721 (23) | 575 (23) | |
| ≥75 | 2680 (48) | 1713 (55) | 967 (38) | |
| Race | ||||
| Non-Hispanic white | 3845 (68) | 2288 (74) | 1557 (62) | <.001 |
| Non-Hispanic black | 860 (15) | 341 (11) | 519 (21) | |
| Hispanic | 347 (6) | 159 (5) | 188 (7) | |
| Other | 235 (4) | 139 (4) | 96 (4) | |
| Unknown | 327 (6) | 174 (6) | 153 (6) | |
| BMI | ||||
| Underweight | 239 (4) | 114 (4) | 125 (5) | <.001 |
| Normal | 1702 (30) | 1006 (32) | 696 (28) | |
| Overweight | 1716 (31) | 984 (32) | 732 (29) | |
| Obese | 1467 (26) | 763 (25) | 704 (28) | |
| Morbid obese | 490 (9) | 234 (8) | 256 (10) | |
| Medical condition | ||||
| Asthma | 945 (17) | 529 (17) | 416 (17) | .64 |
| Chronic lung disease | 1890 (34) | 1134 (37) | 756 (30) | <.001 |
| Cardiovascular disease | 2913 (52) | 1726 (56) | 1187 (47) | <.001 |
| Chronic metabolic disease | 2513 (45) | 1464 (47) | 1049 (42) | <.001 |
| Neurologic disease | 963 (17) | 555 (18) | 408 (16) | .11 |
| Immunosuppression | 921 (16) | 581 (19) | 340 (14) | <.001 |
| Blood disorder | 106 (2) | 74 (2) | 32(1) | <.01 |
| Renal disease | 1101 (20) | 708 (23) | 393 (16) | <.001 |
| Liver disease | 119 (2) | 62 (2) | 57 (2) | .55 |
| ≥1 | 5092 (91) | 2883 (93) | 2209 (88) | <.001 |
| Alcohol abuse status | ||||
| Current | 183 (3) | 70 (2) | 113 (5) | <.001 |
| Former | 185 (3) | 100 (3) | 85 (3) | |
| Never | 5246 (93) | 2931 (95) | 2315 (92) | |
| Smoking status | ||||
| Current | 1051 (19) | 454 (15) | 597 (24) | <.001 |
| Former | 1793 (32) | 1106 (36) | 687 (27) | |
| Never | 2770 (49) | 1541 (50) | 1229 (49) | |
| Influenza virus type(s) | ||||
| Influenza A | 4689 (84) | 2637 (85) | 2052 (82) | <.01b |
| Influenza B | 901 (16) | 454 (15) | 447 (18) | |
| Influenza A and B | 8 (0.1) | 4 (0.1) | 4 (0.2) | |
| Influenza A/B (not distinguished) | 16 (0.3) | 6 (0.2) | 10 (0.4) | |
| Antiviral treatment | 4631 (82) | 2607 (84) | 2024 (81) | <.001 |
| Admitted to the ICU | 803 (14) | 439 (14) | 364 (15) | .76 |
| Deceased | 118 (2) | 61 (2) | 57 (2) | .20b |
| Diagnosis of pneumoniac | 1806 (33) | 1022 (34) | 784 (32) | .19 |
| Length of ICU stay, d, median (IQR) | 3 (1–6) | 2 (1–5) | 3 (1–6) | .14d |
| Length of hospital stay, d, median (IQR) | 3 (2–6) | 3 (2–6) | 3 (2–6) | .07d |
Data are no. (%) of subjects, unless otherwise indicated, and were obtained from the Influenza Hospitalization Surveillance Network. Percentages reflect calculations involving subjects for whom data on the specified characteristic were available and might not sum to 100%, because of rounding.
Abbreviations: BMI, body mass index; ICU, intensive care unit; IQR, interquartile range.
a By the χ2 test, unless otherwise indicated.
b By the Fisher test.
c Among those who underwent chest radiography within 3 days of admission (n = 5462).
d By the Wilcoxon–Mann–Whitney test.