Table 2.
Characteristics of Influenza A(H1N1)pdm09 Cases and Influenza-Negative Controls, US Hospitalized Adult Influenza Vaccine Effectiveness Network (HAIVEN), 2018–2019 (n = 2447)
| Characteristic | Influenza A(H1N1)pdm09 Cases | Influenza-Negative Controls | P Valuea | Standardized Differenceb |
|---|---|---|---|---|
| No. | 225 | 2222 | ||
| Site | <.001 | 0.54 | ||
| Central Texas | 31 (13.8) | 794 (35.7) | ||
| Southeast Michigan | 57 (25.3) | 500 (22.5) | ||
| Western Pennsylvania | 96 (42.7) | 630 (28.4) | ||
| Central Tennessee | 41 (18.2) | 298 (13.4) | ||
| Baseline characteristics | ||||
| Demographics and behavioral risk factors | ||||
| Age groupc | .116 | 0.15 | ||
| 18 to ≤56 y | 87 (38.7) | 745 (33.5) | ||
| >56 to ≤69 y | 79 (35.1) | 752 (33.8) | ||
| >69 y | 59 (26.2) | 725 (32.6) | ||
| Age, y, mean (SD) | 60.11 (15.38) | 61.66 (16.49) | .178 | 0.10 |
| Female | 118 (52.4) | 1246 (56.1) | .33 | 0.07 |
| Black race | 61 (27.1) | 585 (26.3) | .861 | 0.02 |
| Community dwelling | 213 (94.7) | 2095 (94.3) | .932 | 0.02 |
| Insured | 209 (92.9) | 2106 (94.8) | .298 | 0.08 |
| Current tobacco smoking | 50 (22.2) | 602 (27.1) | .135 | 0.11 |
| Current vaping/e-cigarette use | 14 (6.2) | 116 (5.2) | .63 | 0.04 |
| Comorbid health conditionsd | ||||
| Obstructive lung disease | 89 (39.6) | 1188 (53.5) | <.001 | 0.28 |
| Nonobstructive lung disease | 71 (31.6) | 1001 (45.0) | <.001 | 0.28 |
| Heart disease | 107 (47.6) | 1431 (64.4) | <.001 | 0.34 |
| Congestive heart failure | 48 (21.3) | 772 (34.7) | <.001 | 0.30 |
| Neurologic disorder | 59 (26.2) | 790 (35.6) | .006 | 0.20 |
| Renal disorders | 77 (34.2) | 935 (42.1) | .027 | 0.16 |
| Malignancy | 48 (21.3) | 540 (24.3) | .362 | 0.07 |
| Hematologic disorders | 27 (12.0) | 244 (11.0) | .724 | 0.03 |
| Metabolic disorders | 117 (52.0) | 1308 (58.9) | .055 | 0.14 |
| Diabetes/obesity/endocrine disorders | 157 (69.8) | 1673 (75.3) | .083 | 0.12 |
| Health status indicators | ||||
| Number of ACIP high-risk conditions, mean (SD) | 4.52 (3.09) | 5.62 (3.23) | <.001 | 0.35 |
| Charlson Comorbidity Index, mean (SD) | 2.50 (2.91) | 3.28 (3.00) | <.001 | 0.26 |
| Frailty score (0–5), mean (SD) | 1.70 (1.46) | 2.02 (1.46) | .002 | 0.22 |
| Home oxygen use | 39 (17.5) | 629 (28.5) | .001 | 0.26 |
| ≥1 hospitalization in prior year (self-report) | 103 (45.8) | 1412 (63.5) | <.001 | 0.36 |
| Self-reported chemotherapy/radiation, immunosuppressive medications | 68 (30.2) | 904 (40.7) | .003 | 0.22 |
| Immunosuppression by ICD-10 code and/or self-report | 90 (40.0) | 1153 (51.9) | .001 | 0.24 |
| Influenza vaccination habite | <.001 | 0.35 | ||
| Never/rarely | 84 (37.3) | 484 (21.8) | ||
| Sometimes | 10 (4.4) | 150 (6.8) | ||
| Always/almost always | 131 (58.2) | 1588 (71.5) | ||
| Vaccination habit score (0–2), mean (SD) | 1.21 (0.96) | 1.50 (0.83) | <.001 | 0.32 |
| Influenza vaccination status | ||||
| Vaccinated by documentation or plausible self-reportf | 118 (52.4) | 1568 (71.5) | <.001 | 0.38 |
| Vaccinated by self-reportg | 113 (50.2) | 1540 (69.3) | <.001 | 0.40 |
| Admission characteristics | ||||
| Days from illness onset to admission, mean (SD) | 2.83 (2.13) | 2.92 (2.40) | .556 | 0.04 |
| Admitted to tertiary care hospital | 98 (43.6) | 1226 (55.2) | .001 | 0.23 |
| Presented with influenza-like illnessh | 145 (64.4) | 888 (40.0) | <.001 | 0.51 |
| Admitted to intensive care unit | 30 (13.3) | 267 (12.0) | .646 | 0.04 |
| Length of hospital stay, d, mean (SD) | 4.37 (3.77) | 4.92 (4.51) | .074 | 0.13 |
| Died in hospital | 4 (1.8) | 26 (1.2) | .637 | 0.05 |
Data are presented as No. (%) unless otherwise indicated.
Abbreviations: ACIP, Advisory Committee on Immunization Practices; ICD-10, International Classification of Diseases, 10th Edition; SD, standard deviation.
a P value for test of difference across case and control groups based on χ 2 statistic for categorical variables,
t test for difference of means of normally distributed continuous variables, and nonparametric log-rank test for nonnormally distributed continuous variables.
bStandardized absolute mean differences >0.10 shown in bold; standardized differences ≤0.10 are generally considered negligible differences between groups.
cAge groups defined by tertile of age distribution of all subjects.
dDerived from ICD-10 codes associated with inpatient and outpatient medical encounters in the year prior to enrollment admission.
eDefined by patient self-report during enrollment interview.
fPlausible self-report defined as affirmative self-report of current season vaccination including known or approximate date and location of vaccination.
gSelf-report defined as affirmative self-report of current season vaccination including known or approximate date.
hInfluenza-like illness defined as self-reported subjective fever/feverishness plus cough or sore throat.