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Comparative Study
. 2010 Sep;16(9):1388-95.
doi: 10.3201/eid1609.100076.

Comparison of pandemic (H1N1) 2009 and seasonal influenza, Western Australia, 2009

Dale Carcione  1 , Carolien Giele, Gary K Dowse, Donna B Mak, Leigh Goggin, Kelly Kwan, Simon Williams, David Smith, Paul Effler
Affiliations
Comparative Study

Comparison of pandemic (H1N1) 2009 and seasonal influenza, Western Australia, 2009

Dale Carcione et al. Emerg Infect Dis. 2010 Sep.

Abstract

We compared confirmed pandemic (H1N1) 2009 influenza and seasonal influenza diagnosed in Western Australia during the 2009 influenza season. From 3,178 eligible reports, 984 pandemic and 356 seasonal influenza patients were selected; 871 (88.5%) and 288 (80.9%) were interviewed, respectively. Patients in both groups reported a median of 6 of 11 symptoms; the difference between groups in the proportion reporting any given symptom was < or =10%. Fewer than half the patients in both groups had > or =1 underlying condition, and only diabetes was associated with pandemic (H1N1) 2009 influenza (odds ratio [OR] 1.9, 95% confidence interval [CI] 1.1-3.5). A total of 129 (14.8%) persons with pandemic (H1N1) 2009 and 36 (12.5%) persons with seasonal influenza were hospitalized (p = 0.22). After controlling for age, we found that patient hospitalization was associated with pandemic (H1N1) 2009 influenza (OR 1.5; 95% CI 1.1-2.1). Contemporaneous pandemic and seasonal influenza infections were substantially similar in terms of patients' symptoms, risk factors, and proportion hospitalized.

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Figures

Figure 1
Figure 1
Number of notifications for pandemic and seasonal influenza, by date of onset and type, Western Australia, May 22–September 11, 2009. Influenza subtypes reported during the study period (n = 3,178): pandemic (H1N1) 2009, 2,794 (87.9%); influenza A (H3N2), 253 (8.0%); seasonal influenza A (H1N1), 89 (2.8%); influenza B, 36 (1.1%); and seasonal influenza A (not subtyped), 6 (0.2%).
Figure 2
Figure 2
Recruitment of pandemic and seasonal influenza study participants, Western Australia, 2009.
Figure 3
Figure 3
Age distribution for study participants, by influenza type, Western Australia, 2009.
Figure 4
Figure 4
Number of symptoms reported by study participants with influenza, by influenza type, Western Australia, 2009.
Figure 5
Figure 5
Number of underlying medical conditions reported by study participants, by influenza type, Western Australia, 2009.
Figure 6
Figure 6
Duration of hospital stay for study participants, by influenza type, Western Australia, 2009.
See this image and copyright information in PMC

Comment in

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