Table 2. Characteristics of Influenza Cases and Unmatched Test-Negative Controls.
| Characteristic | Cases | Controls | Crude odds ratio |
| n (%) | n (%) | (95% CI) | |
| Sex | |||
| Male | 432 (71.6) | 356 (80.5) | 0.61 (0.45–0.82) |
| Female | 171 (28.4) | 86 (19.5) | Ref |
| Age group | |||
| <25 | 181 (30.0) | 210 (47.5) | Ref |
| 25–29 | 159 (26.4) | 89 (20.1) | 2.07 (1.49–2.87) |
| 30–39 | 195 (32.3) | 113 (25.6) | 2.00 (1.47–2.72) |
| 40+ | 68 (11.3) | 30 (6.8) | 2.63 (1.64–4.22) |
| Race-ethnicity | |||
| White | 358 (59.4) | 316 (71.5) | Ref |
| Black | 107 (17.7) | 56 (12.7) | 1.69 (1.18–2.41) |
| Hispanic | 62 (10.3) | 20 (4.5) | 2.74 (1.62–4.63) |
| Asian/Pacific Islander | 32 (5.3) | 19 (4.3) | 1.49 (0.83–2.67) |
| American Indian/Alaskan Native | 6 (1.0) | 11 (2.5) | 0.48 (0.18–1.32) |
| Other/Unknown | 38 (6.3) | 20 (4.5) | 1.68 (0.96–2.94) |
| Service | |||
| Army | 237 (39.3) | 25 (5.7) | Ref |
| Air Force | 282 (46.8) | 374 (84.6) | 0.08 (0.05–0.12) |
| Marine Corps | 19 (3.1) | 16 (3.6) | 0.12 (0.06–0.27) |
| Navy | 53 (8.8) | 25 (5.7) | 0.22 (0.12–0.42) |
| Coast Guard | 12 (2.0) | 2 (0.4) | 0.63 (0.13–2.99) |
| Number of prior vaccinations | |||
| 0 | 68 (11.3) | 88 (19.9) | Ref |
| 1+ | 535 (88.7) | 354 (80.1) | 1.96 (1.39–2.76) |
| Month of diagnosis | |||
| September | 18 (3.0) | 41 (9.3) | – |
| October | 19 (3.1) | 52 (11.8) | – |
| November | 21 (3.5) | 53 (12.0) | – |
| December | 58 (9.6) | 55 (12.4) | – |
| January | 174 (28.9) | 76 (17.2) | – |
| February | 199 (33.0) | 74 (16.7) | – |
| March | 95 (15.7) | 68 (15.4) | – |
| April | 19 (3.1) | 23 (5.2) | – |
Bolded cells indicate statistical significance.