Table 1.
Descriptive Characteristics of Participants With Medically Attended Acute Respiratory Illness by Influenza Case Status
| Characteristic | Influenza-Negative Controls | Influenza-Positive Cases | A/H3N2 Positive Cases | Influenza B Positive Cases | P Valuea |
|---|---|---|---|---|---|
| N = 7078 | N = 2233 | N = 1817 | N = 395 | ||
| N (Column %) | N (Column %) | N (Column %) | N (Column %) | ||
| Site | <.001 | ||||
| Michigan | 1152 (16.3) | 331 (14.8) | 307 (16.9) | 18 (4.6) | |
| Pennsylvania | 1024 (14.5) | 469 (21.0) | 424 (23.3) | 42 (10.6) | |
| Texas | 1318 (18.6) | 374 (16.8) | 280 (15.4) | 89 (22.5) | |
| Washington | 2272 (32.1) | 500 (22.4) | 416 (22.9) | 82 (20.8) | |
| Wisconsin | 1312 (18.5) | 559 (25.0) | 390 (21.5) | 164 (41.5) | |
| Age, y | <.001 | ||||
| 6 mo–8 | 1946 (27.5) | 473 (21.2) | 396 (21.8) | 72 (18.2) | |
| 9–17 | 950 (13.4) | 392 (17.6) | 306 (16.8) | 80 (20.3) | |
| 18–49 | 2206 (31.2) | 642 (28.8) | 531 (29.2) | 106 (26.8) | |
| 50–64 | 1118 (15.8) | 378 (16.9) | 281 (15.5) | 94 (23.8) | |
| ≥65 | 858 (12.1) | 348 (15.6) | 303 (16.7) | 43 (10.9) | |
| Male | 2969 (42.0) | 954 (42.7) | 767 (42.2) | 179 (45.3) | .52 |
| Race/ethnicityb | .001 | ||||
| White, non-Hispanic | 5182 (73.4) | 1706 (76.6) | 1397 (77.1) | 300 (76.1) | |
| Black, non-Hispanic | 522 (7.4) | 166 (7.5) | 133 (7.3) | 29 (7.4) | |
| Hispanic | 685 (9.7) | 155 (7.0) | 119 (6.6) | 32 (8.1) | |
| Other, non-Hispanic | 673 (9.5) | 199 (8.9) | 162 (9.0) | 33 (8.4) | |
| High-risk condition in last 12 mo (International Classification of Diseases, 9th Edition, Clinical Modification) | |||||
| Any high-risk condition | 2636 (37.2) | 812 (36.4) | 671 (36.9) | 135 (34.2) | .45 |
| Asthma/pulmonary | 1525 (21.6) | 423 (18.9) | 349 (19.2) | 71 (18.0) | .008 |
| Cardiovascular | 773 (10.9) | 247 (11.1) | 204 (11.2) | 41 (10.4) | .85 |
| Diabetes | 504 (7.1) | 194 (8.7) | 164 (9.0) | 26 (6.6) | .01 |
| Morbid obesity (body mass index ≥ 40 kg/m2) | 527 (7.5) | 161 (7.2) | 125 (6.9) | 35 (8.9) | .71 |
| Other | 881 (12.5) | 291 (13.0) | 234 (12.9) | 55 (13.9) | .47 |
| Interval from onset to enrollment | <.001 | ||||
| 0–2 d | 1904 (26.9) | 964 (43.2) | 839 (46.2) | 118 (29.9) | |
| 3–4 d | 2771 (39.2) | 836 (37.4) | 638 (35.1) | 191 (48.4) | |
| 5–7 d | 2403 (34.0) | 433 (19.4) | 340 (18.7) | 86 (21.8) | |
| Reported general health statusc | .006 | ||||
| Excellent/very good | 4991 (70.6) | 1671 (73.9) | 1342 (74.2) | 291 (73.7) | |
| Good | 1639 (23.2) | 459 (20.3) | 368 (20.3) | 80 (20.3) | |
| Fair/poor | 442 (6.3) | 123 (5.4) | 99 (5.5) | 24 (6.1) | |
| Self/household exposure to smoked | 1248 (17.7) | 295 (13.2) | 229 (12.6) | 63 (16.0) | <.001 |
| Number of children aged <12 y in householde | .17 | ||||
| 0 | 4244 (60.0) | 1346 (60.5) | 1101 (60.9) | 233 (59.0) | |
| 1 | 1672 (23.6) | 489 (22.0) | 398 (22.0) | 86 (21.8) | |
| ≥2 | 1156 (16.4) | 390 (17.5) | 310 (17.1) | 76 (19.2) | |
| Reported current health assessment, median (interquartile range)f | |||||
| Scale 1 (worst)–100 (best) | 60 (45–75) | 50 (40–70) | 50 (40–70) | 50 (40–70) | <.001 |
| Vaccination status 2014–2015g | |||||
| Any inactivated vaccine | 3438 (48.6) | 962 (43.1) | 823 (45.3) | 130 (32.9) | |
| Vaccinated with IIV3 | 1397 | 405 | 335h | 66h | |
| Vaccinated with IIV4 | 1628 | 413 | 360h | 48h | |
| Vaccinated with LAIV4 | 394 (5.6) | 123 (5.5) | 108 (5.9) | 10 (2.5) | |
| Vaccinated with other/unknown type | 34 (0.5) | 13 (0.6) | 8 (0.4) | 5 (1.3) | |
| Unvaccinated | 3212 (45.4) | 1135 (50.8) | 878 (48.3) | 250 (63.3) | |
The interquartile range represents the 25th–75th percentile.
Abbreviations: IIV3/4, inactivated influenza vaccine, trivalent/quadrivalent; LAIV4, live attenuated influenza vaccine.
a The χ2 statistic was used to assess the differences between the number of persons with influenza-negative and influenza-positive test results with respect to the distributions of site, age group, sex, race/ethnicity, presence of any high-risk condition, vaccination status, interval from illness onset to enrollment, general health status, smoke exposure in self/household, and number of children aged <12 years in the household. The Wilcoxon Mann–Whitney test was used to assess differences with respect to the distribution of the current health assessment. P < .05 is statistically significant and bolded.
b Data on race/ethnicity were missing for 23 enrollees.
c Data on general health status were missing for 14 enrollees.
d Data on exposure to smoke were missing for 14 enrollees.
e Data on children aged <12 years in the household were missing for 14 enrollees.
f Data on current health assessment were missing for 17 enrollees.
g Vaccination status (14 days or more prior to onset) determined by electronic immunization record (includes electronic medical records, employee health records, and state immunization registry).
h Some influenza cases were caused by A/H1N1 influenza, were unsubtyped, or were coinfections.