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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.

Main Article

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Main Article

Page created: August 15, 2011
Page updated: August 15, 2011
Page reviewed: August 15, 2011
The conclusions, findings, and opinions expressed by authors contributing to this journal do not necessarily reflect the official position of the U.S. Department of Health and Human Services, the Public Health Service, the Centers for Disease Control and Prevention, or the authors' affiliated institutions. Use of trade names is for identification only and does not imply endorsement by any of the groups named above.
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