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

• Published in: Emerging infectious diseases Vol. 16; no. 9; pp. 1388 - 1395
• Main Authors: Carcione, Dale, Giele, Carolien, Dowse, Gary K, Mak, Donna B, Goggin, Leigh, Kwan, Kelly, Williams, Simon, Smith, David, Effler, Paul
• Format: Journal Article
• Language: English
• Published: United States U.S. National Center for Infectious Diseases 01.09.2010; Centers for Disease Control and Prevention
• Subjects: Adolescent; Adult; Aged; Australia; Child; Child, Preschool; Diabetes Complications - epidemiology; Diagnosis; Disease transmission; Distribution; Epidemics; Female; H1N1; Humans; Infant; Infant, Newborn; Influenza; Influenza A Virus, H1N1 Subtype; Influenza, Human - complications; Influenza, Human - epidemiology; Male; Middle Aged; pandemic; Pandemics; Physiological aspects; respiratory infections; Risk Factors; seasonal influenza; Seasons; Viruses; Western Australia - epidemiology; Young Adult; Western Australia; Australia
• ISSN: 1080-6040; 1080-6059
• DOI: 10.3201/eid1609.100076

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.