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.