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Volume 17, Number 8—August 2011

Research

Case–Control Study of Risk Factors for Hospitalization Caused by Pandemic (H1N1) 2009

Kate A. Ward, Paula J. SpokesComments to Author , and Jeremy M. McAnulty
Author affiliations: Author affiliation: New South Wales Department of Health, Sydney, New South Wales, Australia

Main Article

Table A1

Comparison of characteristics for case-patients and controls in a study of risk for hospitalization because of pandemic (H1N1) 2009 influenza, Sydney, Australia, 2009*

Variable
No. (%) case-patients, n = 302
No. (%) controls, n = 603
OR (95% CI)
p value
Sex
F 177 (59) 396 (66) Referent
M
125 (41)
207 (34)
1.4 (1.0–1.8)
0.0379
Age, y
16–25 40 (13) 61 (10) 2.4 (1.4–4.1)
26–35 54 (18) 92 (15) 2.1 (1.3–3.5)
36–45 58 (19) 111 (18) 1.9 (1.2–3.1)
46–55 72 (24) 111 (18) 2.3 (1.4–3.8)
56–65 44 (15) 105 (17) 1.5 (0.9–2.5)
>65
34 (11)
123 (20)
Referent
0.007
Area of residence in Sydney
South East 34 (11) 71 (12)
West 112 (37) 229 (38)
South West 123 (41) 239 (40)
North
33 (11)
64 (11)


Aboriginal status
Nonindigenous 293 (97) 596 (99) Referent
Indigenous
9 (3)
7 (1)
2.6 (1–7.1)
0.0591
Body mass index†
Underweight (<18.5) 15 (5) 15 (3) 3.0 (1.4–6.5) <0.0001
Normal (18.5–24.9) 85 (30) 259 (45) Referent
Overweight (25.0–29.9) 77 (27) 175 (30) 1.3 (0.9–1.9)
Obese 1 (30–34.9) 51 (18) 79 (14) 2.0 (1.3–3.0)
Obese 2 (35–39.9) 31 (11) 29 (5) 3.3 (1.9–5.7)
Obese 3 (>40)
27 (10)
21 (4)
3.9 (2.1–7.3)

Concurrent conditions‡
Asthma 114 (38) 93 (15)
No regular medication 25 (8) 48 (8) 1.4 (0.8–2.4) <0.0001
Regular medication 89 (29) 45 (7) 5.4 (3.6–8.0)
Previous hospitalization 48 (16) 24 (4)
Heart disease§ 40 (14) 41 (7) 2.1 (1.3–3.3) 0.0016
Heart failure 8 (20) 1 (2)
Angina 10 (25) 7 (17)
Heart attack 8 (20) 9 (22)
Congenital condition 6 (15) 4 (10)
Rheumatic fever 6 (15) 1 (2)
Kidney disease¶ 10 (3) 8 (1) 2.5 (1.0–6.5) 0.0522
Renal failure 5 (50) 4 (50)
Dialysis 3 (30)
Transplant or waiting list 4 (40)
Mental health problem 53 (18) 49 (8) 2.4 (1.6–3.6) <0.0001
Neurologic problem 24 (8) 42 (7) 1.2 (0.7–1.9) 0.5925
Immunosuppression 30 (10) 22 (4) 2.9 (1.6–5.1) 0.0002
Obstructive sleep apnea 37 (12) 23 (4) 3.5 (2.1–6.0) <0.0001
Lung disease 58 (19) 31 (5) 4.4 (2.8–7.0) <0.0001
Regular medication 39 (67) 13 (42)
Previous hospitalization 32 (55) 11 (35)
Diabetes 58 (19) 38 (6) 3.5 (2.3–5.5) <0.0001
Metabolic disorder 3 (1) 7 (1) 0.9 (0.2–3.3) 0.8204
Liver disease 23 (8) 20 (3) 2.4 (1.3–4.4) 0.0053
Blood disorder 16 (5) 16 (3) 2.1 (1.0–4.2) 0.0463
Pregnancy 40 (13) 7 (1) 13.0 (5.7–29.4) <0.0001
First trimester 5 (13) 2 (18)
Second trimester 7 (18) 3 (27)
Third trimester
28 (70)
2 (18)


Smoking status#
Nonsmoker 144 (48) 372 (62) Referent
Current smoker 66 (22) 82 (14) 2.1 (1.4–3.0) 0.0002
Former smoker
91 (30)
149 (25)
1.6 (1.1–2.2)

Influenza vaccine in 2009** 107 (36) 202 (34) 1.1 (0.8–1.5) 0.529

*OR, odds ratio; CI, confidence interval.
†Groups are not mutually exclusive.
‡Body mass index calculated as weight in kilograms divided by height in meters squared. Data were missing for 16 case-patients and 25 controls.
§Data were missing for 6 case-patients and 12 controls.
¶Data were missing for 2 controls.
#Data were missing for 2 case-patients and 2 controls.
**Vaccination information was missing for 2 case-patients and 1 control.

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