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Table 3 Characteristics of included admissions according to RT-PCR result

From: Influenza epidemiology and influenza vaccine effectiveness during the 2015–2016 season: results from the Global Influenza Hospital Surveillance Network

Characteristic n (%)
Influenza negative Any influenza A(H1N1)pdm09 A(H3N2) A not subtyped B/Yamagata B/Victoria B not subtyped
N = 7467 N = 2415 N = 1415 N = 235 N = 180 N = 45 N = 532 N = 33
Age (y), median (IQR) 20 (2–65) 18 (3–46) 19 (2–43) 30 (3–71) 4 (1–42) 37 (4–57) 10 (4–31) 25 (5–56)
 P vs. influenza negative 0.136 0.794 <  0.001 0.001 0.231 <  0.001 0.595
Age groupa
 <  1 y 1138 (15.2) 232 (9.6) 135 (9.5) 16 (6.8) 45 (25.0) 7 (15.6) 32 (6.0) 4 (12.1)
 1–4 y 1823 (24.4) 663 (27.5) 423 (29.9) 49 (20.9) 47 (26.1) 5 (11.1) 141 (26.5) 3 (9.1)
 5–17 y 613 (8.2) 295 (12.2) 135 (9.5) 12 (5.1) 15 (8.3) 6 (13.3) 123 (23.1) 8 (24.2)
 18–49 y 1352 (18.1) 649 (26.9) 409 (28.9) 57 (24.3) 33 (18.3) 10 (22.2) 134 (25.2) 7 (21.2)
 50–64 y 645 (8.6) 202 (8.4) 137 (9.7) 25 (10.6) 13 (7.2) 9 (20.0) 17 (3.2) 4 (12.1)
 65–74 y 640 (8.6) 152 (6.3) 71 (5.0) 27 (11.5) 9 (5.0) 5 (11.1) 38 (7.1) 4 (12.1)
 75–84 y 796 (10.7) 160 (6.6) 76 (5.4) 36 (15.3) 12 (6.7) 3 (6.7) 35 (6.6) 1 (3.0)
 ≥ 85 y 459 (6.1) 62 (2.6) 29 (2.0) 13 (5.5) 6 (3.3) 0 (0.0) 12 (2.3) 2 (6.1)
P vs. influenza negative <  0.001 <  0.001 <  0.001 0.008 0.03 <  0.001 0.010
Sex
 Male 4112 (55.1) 1268 (52.5) 738 (52.2) 125 (53.2) 101 (56.1) 24 (53.3) 278 (52.3) 19 (57.6)
 Female 3355 (44.9) 1147 (47.5) 677 (47.8) 110 (46.8) 79 (43.9) 21 (46.7) 254 (47.7) 14 (42.4)
P vs. influenza negative 0.028 0.041 0.569 0.832 0.815 0.208 0.893
Underlying chronic conditions
 No 4869 (65.2) 1737 (71.9) 1038 (73.4) 132 (56.2) 125 (69.4) 22 (48.9) 414 (77.8) 20 (60.6)
 Yes 2598 (34.8) 678 (28.1) 377 (26.6) 103 (43.8) 55 (30.6) 23 (51.1) 118 (22.2) 13 (39.4)
P vs. influenza negative <  0.001 <  0.001 0.004 0.259 0.022 <  0.001 0.490
Hospitalized within ≤12 mo
 No 5390 (72.2) 1778 (73.6) 1066 (75.3) 160 (68.1) 113 (62.8) 33 (73.3) 405 (76.1) 19 (57.6)
 Yes 2077 (27.8) 637 (26.4) 349 (24.7) 75 (31.9) 67 (37.2) 12 (26.7) 127 (23.9) 14 (42.4)
P vs. influenza negative 0.168 0.015 0.168 0.005 0.864 0.049 0.107
Underlying chronic conditions
 Cardiovascular disease 1543 (20.7) 345 (14.3) 188 (13.3) 57 (24.3) 27 (15.0) 12 (26.7) 59 (11.1) 6 (18.2)
P vs. influenza negative <  0.001 <  0.001 0.182 0.068 0.322 <  0.001 0.79
 Chronic obstructive pulmonary disease 860 (11.5) 179 (7.4) 88 (6.2) 37 (15.7) 13 (7.2) 5 (11.1) 35 (6.6) 5 (15.2)
P vs. influenza negative <  0.001 <  0.001 0.047 0.077 1.0 <  0.001 0.409
 Asthma 339 (4.5) 85 (3.5) 46 (3.3) 12 (5.1) 13 (7.2) 2 (4.4) 12 (2.3) 2 (6.1)
P vs. influenza negative 0.031 0.029 0.682 0.086 1.0 0.013 0.656
 Immunodeficiency/organ transplant 66 (0.9) 26 (1.1) 14 (1.0) 6 (2.6) 2 (1.1) 1 (2.2) 2 (0.4) 1 (3.0)
P vs. influenza negative 0.391 0.698 0.009 0.674 0.333 0.325 0.250
 Diabetes 704 (9.4) 136 (5.6) 72 (5.1) 21 (8.9) 12 (6.7) 7 (15.6) 23 (4.3) 4 (12.1)
P vs. influenza negative <  0.001 <  0.001 0.799 0.216 0.162 <  0.001 0.538
 Chronic renal impairment 336 (4.5) 118 (4.9) 63 (4.5) 17 (7.2) 12 (6.7) 3 (6.7) 22 (4.1) 4 (12.1)
P vs. influenza negative 0.431 0.941 0.048 0.162 0.456 0.694 0.055
 Chronic neuromuscular disease 151 (2.0) 61 (2.5) 33 (2.3) 11 (4.7) 7 (3.9) 1 (2.2) 9 (1.7) 1 (3.0)
P vs. influenza negative 0.138 0.451 0.005 0.079 0.603 0.599 0.481
 Active neoplasm 245 (3.3) 59 (2.4) 33 (2.3) 12 (5.1) 3 (1.7) 0 (0.0) 11 (2.1) 0 (0.0)
P vs. influenza negative 0.038 0.061 0.125 0.289 0.404 0.124 0.626
 Chronic liver disease 103 (1.4) 34 (1.4) 28 (2.0) 3 (1.3) 1 (0.6) 1 (2.2) 1 (0.2) 0 (0.0)
P vs. influenza negative 0.917 0.086 1.0 0.522 0.467 0.015 1.0
 Autoimmune disease 75 (1.0) 29 (1.2) 19 (1.3) 6 (2.6) 1 (0.6) 0 (0.0) 3 (0.6) 0 (0.0)
P vs. influenza negative 0.411 0.253 0.022 1.0 1.0 0.489 1.0
 Pregnant (women 15–45 y) 337 (4.5) 278 (11.5) 188 (13.3) 22 (9.4) 2 (1.1) 0 (0.0) 62 (11.7) 4 (12.1)
P vs. influenza negative <  0.001 <  0.001 0.014 0.107 0.062 <  0.001 0.373
 Obeseb,c 1089 (14.6) 336 (13.9) 208 (14.7) 25 (10.6) 31 (17.2) 11 (24.4) 59 (11.1) 4 (12.1)
P vs. influenza negative 0.47 0.84 0.124 0.311 0.063 0.025 1.0
Outpatient consultations within ≤3 mod
 0 1478 (19.8) 673 (27.9) 447 (31.6) 44 (18.7) 56 (31.1) 8 (17.8) 120 (22.6) 7 (21.2)
 1 1305 (17.5) 468 (19.4) 303 (21.4) 27 (11.5) 43 (23.9) 7 (15.6) 86 (16.2) 4 (12.1)
 ≥ 2 2880 (38.6) 920 (38.1) 556 (39.3) 82 (34.9) 81 (45.0) 18 (40.0) 171 (32.1) 22 (66.7)
P vs. influenza negative <  0.001 <  0.001 0.284 0.207 0.914 0.039 0.238
Smoking (≥ 18 y)e
 Never smoked 1881 (25.2) 667 (27.6) 391 (27.6) 96 (40.9) 35 (19.4) 17 (37.8) 121 (22.7) 9 (27.3)
 Past smoker 1104 (14.8) 300 (12.4) 180 (12.7) 41 (17.4) 14 (7.8) 5 (11.1) 60 (11.3) 5 (15.2)
 Current smoker 897 (12.0) 241 (10.0) 141 (10.0) 14 (6.0) 24 (13.3) 5 (11.1) 55 (10.3) 4 (12.1)
P vs. influenza negative <  0.001 0.006 <  0.001 0.111 0.371 0.582 1.0
Functional impairment status (Barthel index, ≥ 65 y)f
 Total (0–15) 160 (2.1) 20 (0.8) 7 (0.5) 5 (2.1) 4 (2.2) 1 (2.2) 4 (0.8) 0 (0.0)
 Severe (20–35) 69 (0.9) 8 (0.3) 2 (0.1) 2 (0.9) 0 (0.0) 1 (2.2) 3 (0.6) 0 (0.0)
 Moderate (40–55) 129 (1.7) 25 (1.0) 14 (1.0) 6 (2.6) 2 (1.1) 0 (0.0) 4 (0.8) 0 (0.0)
 Mild (60–90) 469 (6.3) 85 (3.5) 35 (2.5) 25 (10.6) 10 (5.6) 0 (0.0) 13 (2.4) 3 (9.1)
 Minimal (95–100) 847 (11.3) 201 (8.3) 107 (7.6) 24 (10.2) 11 (6.1) 5 (11.1) 52 (9.8) 4 (12.1)
P vs. influenza negative 0.021 0.002 0.244 0.55 0.17 0.053 0.893
Time from onset of symptoms to swabbingg
 0–2 d 2384 (31.9) 1017 (42.1) 663 (46.9) 89 (37.9) 68 (37.8) 10 (22.2) 188 (35.3) 11 (33.3)
 3–4 d 2514 (33.7) 797 (33.0) 446 (31.5) 68 (28.9) 70 (38.9) 15 (33.3) 189 (35.5) 15 (45.5)
 5–7 d 2260 (30.3) 543 (22.5) 277 (19.6) 68 (28.9) 33 (18.3) 20 (44.4) 144 (27.1) 5 (15.2)
 8–9 d 300 (4.0) 50 (2.1) 24 (1.7) 8 (3.4) 7 (3.9) 0 (0.0) 11 (2.1) 1 (3.0)
P vs. influenza negative <  0.001 <  0.001 0.222 0.009 0.107 0.031 0.229
Influenza vaccination ≥14 d from ILI onseth,i 1235 (16.5) 243 (10.1) 108 (7.6) 22 (9.4) 17 (9.4) 6 (13.3) 81 (15.2) 11 (33.3)
P vs. influenza negative 0.207 0.559 0.007 0.41 1.0 1.0 1.0
  1. Abbreviations: ILI influenza-like illness, IQR interquartile range
  2. a1 missing for influenza negative
  3. bDetermined from the body mass index according to age and sex following the World Health Organization guidelines [12]
  4. c12 missing for influenza negative, 10 for A(H1N1)pdm09 and 7 for A(H3N2)
  5. d1 missing for any influenza and 1 for A(H1N1)pdm09; Beijing not included
  6. e11 missing for influenza negative, 17 for any influenza, 10 for A(H1N1)pdm09, and 7 for A(H3N2)
  7. f222 missing for influenza negative, 35 for any influenza, 11 for A(H1N1)pdm09, 14 for A(H3N2), 1 for B/Yamagata, and 9 for B/Victoria
  8. g9 missing or > 10 d for influenza negative, 8 for any influenza, 5 for A(H1N1)pdm09, 2 for A(H3N2), 2 for A not subtyped, and 1 for B not subtyped
  9. hOnly vaccinated patients
  10. i2 missing for any influenza, 1 for A(H3N2), and 1 for B/Victoria