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. 2016 May 19;11(5):e0154970. doi: 10.1371/journal.pone.0154970

Table 3. Risk of admission with influenza by site, strain, and patient-related characteristics.

Influenza positive Crude OR Heterogeneity by strain (I2) Adjusted OR
Variable/characteristic N n % Value 95% CI Value 95% CI
Days from onset of symptoms to swabbinga
    0–2 days 2034 465 22.9 1.00 63.20% 1.00
    3–4 days 2013 418 20.8 0.88 0.76 1.03 72.10% 0.80 0.69 0.94
    5–7 days 1256 203 16.2 0.65 0.54 0.78 19.40% 0.55 0.45 0.67
Ageb
    0–5 months 557 54 9.7 1.00 0.0% 1.00
    6–11 months 315 36 11.4 1.20 0.77 1.88 0.0% 1.21 0.77 1.90
    1–4 years 1086 181 16.7 1.86 1.35 2.57 0.0% 1.90 1.36 2.64
    5–17 years 393 102 26.0 3.26 2.28 4.68 0.0% 3.64 2.50 5.30
    18–49 years 1278 349 27.3 3.50 2.58 4.75 0.0% 3.95 2.84 5.49
    50–64 years 469 132 28.1 3.65 2.58 5.15 68.6% 3.71 2.54 5.44
    65–74 years 398 94 23.6 2.88 2.00 4.14 0.0% 3.13 2.07 4.74
    75–84 years 532 106 19.9 2.32 1.63 3.30 0.0% 2.51 1.67 3.79
    ≥85 years 275 32 11.6 1.23 0.77 1.95 17.0% 1.39 0.83 2.32
Sexc
    Male 2927 539 18.4 1.00 0.0% 1.00
    Female 2376 547 23.0 1.33 1.16 1.51 0.0% 1.28 1.11 1.49
    Female, non-pregnant 2039 391 19.1 1.05 0.91 1.21 0.0% 1.02 0.87 1.19
Other risk factorsd
    One or more 1858 430 23.4 1.28 1.12 1.47 17.90% 1.29 1.05 1.58
    Cardiovascular disease 874 189 21.62 1.37 1.14 1.65 39.6% 1.64 1.33 2.02
    COPD 746 139 18.63 1.14 0.92 1.40 91.4% 1.31 1.03 1.67
    Asthma 270 76 28.15 1.94 1.47 2.58 27.6% 2.25 1.67 3.03
    Immunosuppression 54 16 29.63 2.09 1.15 3.77 48.4% 2.25 1.23 4.11
    Diabetes 495 105 21.21 1.33 1.06 1.69 92.3% 1.69 1.29 2.23
    Renal disease 224 57 25.45 1.69 1.23 2.32 21.4% 2.11 1.48 3.01
    Rheumatologic disease 23 11 47.83 4.55 1.99 10.38 58.5% 5.55 2.34 13.16
    Neuromuscular 113 19 16.81 1.00 0.61 1.66 28.5% 1.16 0.69 1.95
    Malignancy (active) 159 29 18.24 1.11 0.73 1.67 65.3% 1.18 0.75 1.85
    Liver disease 88 23 26.1 1.75 1.08 2.85 0.0% 1.94 1.18 3.19
    Autoimmune disease 48 16 33.3 2.48 1.35 4.56 0.0% 2.97 1.58 5.59
    Obese 496 123 24.8 1.64 1.31 2.05 81.8% 1.88 1.46 2.41
Pregnancye 337 156 46.29 2.93 2.07 4.14 0.0% 3.84 2.48 5.94
    With comorbidity 50 30 60.0 5.19 2.25 11.99 0.0% 11.90 2.29 61.70
    No other conditions 287 126 43.9 2.64 1.80 3.88 0.0% 3.55 2.21 5.68
Influenza vaccinationf 852 138 16.2 0.71 0.58 0.86 0.0% 0.61 0.48 0.77

Risk of admission with influenza was determined by comparing influenza-positive and influenza-negative admissions. Strains A(H3N2), A(H1N1)pdm09, and B/Yamagata lineage were considered. Admissions with not-subtyped strains or with B/Victoria lineage were not included because of small sample sizes. I2 for the aOR of influenza by site was 0.0%, and the clustering effect by site was P = 1.0..

a Adjusted by sex, age and calendar time splines, comorbidity, hospital admission in previous 12 months, vaccination during the current season, and time to swab.

b Adjusted by health care access, influenza vaccination, underlying conditions, sex, and site as an indicator variable.

c Adjusted by age, comorbidity, smoking habits, socioeconomic status, calendar time, and site as an indicator variable. For heterogeneity estimates, pregnant women were excluded from comparison groups.

d For other risk factors, the first column indicates admissions with the risk factor and influenza positive and the second column indicates the number of subjects with the underlying condition included in the study. The comparison group to estimate the aOR of influenza admission for the risk factor (not shown) is included in admissions without underlying conditions or pregnant, with estimates adjusted for previous vaccination and hospitalizations during the previous 12 months.

e Adjusted by social class, smoking habits, comorbidity, age, and calendar time.

f Adjusted by age, sex, comorbidity, smoking habits, social class, calendar time, time to swab, and site as an indicator variable.