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Volume 16, Number 9—September 2010

Research

Comparison of Pandemic (H1N1) 2009 and Seasonal Influenza, Western Australia, 2009

Dale Carcione, Carolien Giele, Gary K. Dowse, Donna B. Mak, Leigh Goggin, Kelly Kwan, Simon Williams, David Smith, and Paul EfflerComments to Author 
Author affiliations: Author affiliations: Communicable Disease Control Directorate, Perth, Western Australia, Australia (D. Carcione, C. Giele, G.K. Dowse, D.B. Mak, L. Goggin, K. Kwan, P. Effler); PathWest Laboratory Medicine, Nedlands, Western Australia, Australia (S. Williams, D. Smith)

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Table

Symptoms, underlying medical conditions, and medical care reported by study participants in a comparison of pandemic (H1N1) 2009 and seasonal influenza, Western Australia, 2009*

Parameter
No. respondents
Pandemic (H1N1) 2009, no. (%)
Seasonal influenza, no. (%)
RD
Univariate χ2 p value
OR† (95% CI)
p value
Symptoms
Fever‡ 1,159 762 (88) 225 (78) 10 0.001 1.64 (1.15–2.35) 0.01§
Cough 1,159 743 (85) 236 (82) 3 NS 1.45 (1.01–2.34) 0.01§
Myalgia/arthalgia 1,159 565 (65) 173 (60) 5 NS 1.40 (1.06–1.87) 0.02§
Diarrhea 1,159 165 (19) 35 (12) 7 0.008 1.72 (1.15–2.57) 0.01§
Rhinorrhea 1,159 494 (57) 189 (66) −9 0.007 0.60 (0.45–0.80) 0.01§
Sore throat 1,159 488 (56) 169 (59) 3 NS 0.82 (0.62–1.09) 0.17
Shortness of breath 1,159 289 (33) 99 (35) 2 NS 1.14 (0.85–1.53) 0.38
Headache 1,159 537 (62) 176 (61) 1 NS 1.02 (0.77–1.35) 0.91
Vomiting or nausea 1,159 284 (33) 80 (28) 5 NS 1.14 (0.84–1.54) 0.40
Fatigue 1,159 639 (73) 205 (71) 2 NS 1.12(0.83–1.51) 0.47
Rigors 1,159 471 (54) 148 (52) 2 NS 1.13 (0.86–1.48) 0.40
ILI criteria met¶
1,159
706 (81
209 (73)
8
0.002
1.50 (1.09–2.06)
0.01§
Underlying medical conditions
Diabetes 1,032 49 (7) 18 (6) 1 NS 1.93 (1.07–3.51) 0.03§
Heart disease 1,027 34 (5) 20 (7) 2 NS 1.16 (0.63–2.16) 0.63
Respiratory disease 1,031 178 (24) 62 (22) 2 NS 1.33 (0.94–1.87) 0.10
Renal disease 1,028 13 (2) 7 (2) 0 NS 1.17 (0.44–3.10) 0.76
Neurologic disease 1,028 12 (2) 7 (2) 0 NS 0.91 (0.33–2.53) 0.86
Hematologic disorder 1,028 19 (3) 5 (2) 1 NS 2.33 (0.82–6.66) 0.11
Metabolic disease (not diabetes) 1,028 12 (2) 4 (1) 1 NS 1.25 (0.38–4.06) 0.71
Immune impairment 1,028 26 (3) 16 (6) 3 NS 0.88 (0.45–1.71) 0.70
Morbid obesity 1,031 64 (9) 32 (11) 2 NS 1.12 (0.70–1.80) 0.64
Current smoker 1,032 98 (13) 35 (12) 1 NS 1.36 (0.89–2.08) 0.16
Pregnancy (women only) 556 36 (9) 8 (5) 4 NS 1.85 (0.84–4.10) 0.13
Any
1,051
366 (48)
135 (47)
1
NS
1.44 (1.07–1.94)
0.02§
Medical care
Hospitalization 1,159 129 (15) 36 (12) 3 NS 1.58 (1.04–2.39) 0.03§
Antiviral treatment 1,103 388 (47) 71 (26) 21 0.001 3.12 (2.27–4.29) 0.01§

*Totals respondents may not sum to 1,159 for all parameters because questions regarding underlying medical conditions and antiviral treatment were added shortly after the study was initiated, and there are intermittent missing values to individual questions for some respondents. RD, risk difference (absolute difference in the proportion of pandemic and seasonal influenza patients reporting a given parameter); OR, odds ratio; CI, confidence interval; NS, not significant; ILI, influenza–like illness (patient had fever and cough or sore throat).
†ORs were computed by using logistic regression to control for age. Each row depicts data from a separate regression equation, where the dependent variable was defined as influenza type and age (in years) and a single patient characteristic, as listed in the first column of the row (coded as a dichotomous variable indicating the presence or absence of the respective symptom or underlying medical condition) were included as the predictor variables. In all of the logistic analyses performed, age remained significantly associated with influenza type, i.e., younger patients had a higher odds of having pandemic influenza compared with seasonal influenza.
‡Fever was defined as temperature >38°C or subjective fever if temperature was not measured.
§Significant OR obtained using logistic regression.
¶ Patient reported >1 of the underlying medical conditions listed.

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