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Table 3 Proportion of influenza B infections by age group and healthcare setting (Victoria vs Yamagata lineages)*, Italy 2004/2005–2016/2017

From: Co-circulation of the two influenza B lineages during 13 consecutive influenza surveillance seasons in Italy, 2004–2017

VariablesB/Victoria (N = 1267)B/Yamagata (N = 1097)RRcrude(95% CI)RRadj(95% CI)p-value**
n. (%)n. (%)
Median age (IQR)7 (9)13 (41)    < 0.001***
Age group (years)
 0–4302 (23.8)190 (17.3)1.91(1.53–2.39)2.13(1.70–2.67)< 0.001
 5–14655 (51.7)380 (34.7)1.97(1.59–2.45)2.27(1.82–2.84)< 0.001
 15–44198 (15.7)214 (19.5)1.50(1.19–1.90)1.67(1.31–2.12)< 0.001
 45–6454 (4.2)190 (17.3)0.69(0.50–0.95)0.72(0.52–0.99)0.047
  > 6458 (4.6)123 (11.2)RefRef
Healthcare settings
 Community927 (76.6)810 (77.8)RefRef
 Hospitals283 (23.4)231 (22.2)1.03(0.94–1.13)1.24(1.15–1.35)< 0.001
  1. *Crude and adjusted (adj) relative risk (RR) estimated using the univariable and multivariable log-binomial regression model with age bracket of > 64 as a reference class;
  2. CI: confidence interval
  3. **p-value of the multivariable binomial negative model;
  4. ***p-value of the U Mann-Whitney test; p-values of < 0.05 were considered statistically significant
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