When should a diagnosis of influenza be considered in adults requiring intensive care unit admission? Results of population-based active surveillance in Toronto

Table 3 Predictors of influenza infection in adult patients admitted to ICUs^a

	Univariable analysis		Multivariable analysis^b
Predictor	Odds ratio (95% CI)	P value	Odds ratio (95% CI)	P value
Seasonal influenza A and B (2007/2008 and 2008/2009)
Age ≥65 years	1.2 (0.8 to 1.9)	0.37	1.2 (0.8 to 1.9)	0.37
Female gender	1.1 (0.8 to 1.7)	0.53	-	-
Temperature ≥38.0°C upon admission	3.2 (2.0 to 5.2)	<0.001	2.3 (1.4 to 3.9)	0.002
Respiratory symptoms upon admission	4.4 (2.2 to 8.8)	<0.001	-	-
Admission diagnosis
Respiratory infection^c	3.7 (2.4 to 5.7)	<0.001	4.2 (1.6 to 3.7)	<0.001
Respiratory failure^d	2.9 (1.8 to 4.8)	<0.001	4.2 (2.6 to 6.9)	<0.001
Week with >15% positive specimens	2.6 (1.7 to 3.9)	<0.001	2.5 (1.6 to 3.7)	<0.001
Pandemic 2009 H1N1 influenza
Age ≥65 years	0.2 (0.1 to 0.5)	<0.001	0.5 (0.3 to 0.8)	0.004
Female gender	0.5 (0.2 to 1.2)	0.12	-	-
Temperature ≥38.0°C upon admission	7.2 (2.9 to 17.6)	<0.001	4.7 (1.7 to 13.6)	0.004
Respiratory symptoms upon admission	9.3 (1.2 to 70.0)	0.009	-	-
Admission diagnosis			-	-
Respiratory infection^c	8.1 (3.5 to 18.6)	<0.001	7.3 (3.0 to 18.1)	<0.001
Respiratory failure^d	1.1 (0.3 to 3.8)	0.92	-	-
Week with >15% positive specimens	1.4 (0.5 to 4.2)	0.57	-	-

^a95% CI: 95% confidence interval. ^bVariables included in the final model for seasonal and pandemic 2009 H1N1 influenza, respectively, are those where odds ratios and P values are reported in the multivariable analysis. The Akaike Information Criterion values for the final model of seasonal and pandemic 2009 H1N1 influenza, respectively, were 721.4 and 140.0. ^c'Pneumonia' and 'other respiratory infection'. ^d'Chronic obstructive pulmonary disease exacerbation', 'asthma exacerbation' and 'respiratory failure'.

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