Table 2.
Geometric mean antibody titers among adults hospitalized for acute respiratory illness during the 2015–2016 influenza season by subject characteristics.
| Characteristic | Participants No. (%) |
A/Califomia/7/2009 (HlNl)pdmO9 HAI GMT (95% CI) |
P-valuea | A/California/7/2009 (HlNl)pdmO9 NAI GMT (95% CI) |
P-valuea |
|---|---|---|---|---|---|
| Overall | 339 (100.0) | 55.9 (47.9, 65.3) | - | 50.5 (42.5, 59.9) | - |
| Study hospital | |||||
| University of Michigan, Ann Arbor | 243 (71.7) | 56.8 (47.5, 68.0) | 0.754 | 44.8 (36.6, 55.0) | 0.030 |
| Henry Ford, Detroit | 96 (28.3) | 53.8 (39.8, 72.8) | 68.3 (50.1, 93.0) | ||
| Sex | |||||
| Female | 187 (55.2) | 53.6 (43.9, 65.4) | 0.550 | 44.2 (35.5, 55.0) | 0.091 |
| Male | 152 (44.8) | 58.9 (46.3, 75.1) | 59.5 (45.4, 77.9) | ||
| Age category (y) | |||||
| 18–49 | 106 (31.3) | 64.5 (47.1, 88.2) | 0.442 | 35.8 (26.2, 48.8) | <0.001 |
| 50–64 | 122 (36.0) | 54.4 (41.8, 70.7) | 43.8 (32.8, 58.4) | ||
| ≥65 | 111 (32.7) | 50.4 (40.3, 63.0) | 82.0 (62.4, 107.7) | ||
| Race/ethnicityb | |||||
| White (not Hispanic) | 198 (59.3) | 56.0 (46.5, 67.4) | 0.977 | 45.9 (36.8, 57.1) | 0.433 |
| Black | 95 (28.4) | 56.8 (40.6, 79.4) | 58.5 (41.7, 82.0) | ||
| Other | 41 (12.3) | 59.0 (37.3, 93.3) | 56.1 (34.9, 90.2) | ||
| Frailty score (range 0–5) | |||||
| 0–2 | 232 (68.4) | 52.5 (43.7, 63.0) | 0.236 | 48.6 (39.3, 60.0) | 0.513 |
| 3–5 | 107 (31.6) | 64.2 (48.2, 85.4) | 54.9 (41.0, 73.7) | ||
| Charlson comorbidity index category | |||||
| 0 | 41 (12.1) | 36.8 (23.1, 58.5) | 0.230 | 29.0 (19.3, 43.5) | 0.014 |
| 1 | 55 (16.2) | 53.4 (37.0, 77.2) | 35.7 (24.0, 53.1) | ||
| 2 | 45 (13.3) | 57.9 (37.0, 90.6) | 52.8 (32.7, 85.3) | ||
| 3+ | 198 (58.4) | 61.3 (50.3, 74.8) | 61.7 (49.1, 77.7) | ||
| Illness onset to blood collectionc | |||||
| 0–3 days | 194 (58.6) | 58.8 (47.2, 73.3) | 0.538 | 53.8 (42.5, 68.1) | 0.586 |
| 4–6 days | 97 (29.3) | 49.9 (38.5, 64.6) | 43.9 (32.7, 59.0) | ||
| 7–10 days | 40 (12.1) | 47.6 (32.4, 69.9) | 47.6 (28.8, 78.4) | ||
| Influenza vaccination status | |||||
| Vaccinated | 237 (69.9) | 78.8 (66.8, 93.1) | <0.001 | 65.6 (53.9, 79.7) | <0.001 |
| Unvaccinated | 102 (30.1) | 25.2 (19.0, 33.5) | 27.5 (20.1, 37.7) | ||
| Influenza Status | |||||
| A(HlNl)pdm09 Positive | 64 (18.9) | 23.5 (17.2, 32.3) | <0.001 | 23.3 (16.3, 33.3) | <0.001 |
| Negative | 275 (81.1) | 68.4 (57.9, 80.9) | 60.5 (50.1, 73.0) |
Abbreviations: 95% CI, 95% confidence interval; GMT, geometric mean titer; HAI, hemagglutination-inhibition; NAI, neuraminidase-inhibition.
a
P-values are calculated from unbalanced ANOVA F-test.
b
5 participants had missing race/ethnicity data.
c
8 participants had missing time between onset and blood collection.