Table 1. Independent risk factors for hospitalization from pandemic (H1N1) 2009 influenza, all case-patients and controls, Sydney, Australia, 2009*.

Patient characteristic	Adjusted OR (95% CI)	p value
Sex
F	Referent
M	1.8 (1.2–2.5)	0.0017
Age, y
16–25	5.4 (2.5–11.4)
26–35	4.1 (2.0–8.3)
36–45	3.9 (2.0–7.6)	<0.0001
46–55	5.1 (2.7–9.6)
56–65	1.9 (1.0–2.5)
>65	Referent
Underlying condition
Asthma, regular medication	4.3 (2.7–6.8)	<0.0001
Heart disease	2.3 (1.2–4.1)	0.0083
Immunosuppression	5.5 (2.8–10.9)	<0.0001
Lung disease	6.6 (3.8–11.6)	<0.0001
Diabetes	3.8 (2.2–6.5)	<0.0001
Pregnancy	22.4 (9.2–54.5)	<0.0001
Smoking status
Nonsmoker	Referent
Current smoker	2.0 (1.3–3.2)	0.002
Former smoker	2.0 (1.3–3.0)
No. significant risk factors
0	Referent
1	3.9 (2.6–5.8)
2	9.3 (5.9–14.6)	<0.0001
3	20.4 (10.4–40.2)
>4	80.3 (10.1–638.7)

*OR, odds ratio; CI, confidence interval.