Abstract
IntroductionOn May 26, 2009, the first confirmed case of Pandemic (H1N1) 2009 virus (pH1N1) infection in Hunter New England (HNE), New South Wales (NSW), Australia (population 866,000) was identified. We used local surveillance data to estimate pH1N1-associated disease burden during the first wave of pH1N1 circulation in HNE.MethodsSurveillance was established during June 1-August 30, 2009, for: 1) laboratory detection of pH1N1 at HNE and NSW laboratories, 2) pH1N1 community influenza-like illness (ILI) using an internet survey of HNE residents, and 3) pH1N1-associated hospitalizations and deaths using respiratory illness International Classification of Diseases 10 codes at 35 HNE hospitals and mandatory reporting of confirmed pH1N1-associated hospitalizations and deaths to the public health service. The proportion of pH1N1 positive specimens was applied to estimates of ILI, hospitalizations, and deaths to estimate disease burden.ResultsOf 34,177 specimens tested at NSW laboratories, 4,094 (12%) were pH1N1 positive. Of 1,881 specimens from patients evaluated in emergency departments and/or hospitalized, 524 (26%) were pH1N1 positive. The estimated number of persons with pH1N1-associated ILI in the HNE region was 53,383 (range 37,828–70,597) suggesting a 6.2% attack rate (range 4.4–8.2%). An estimated 509 pH1N1-associated hospitalizations (range 388–630) occurred (reported: 184), and up to 10 pH1N1-associated deaths (range 8–13) occurred (reported: 5). The estimated case hospitalization ratio was 1% and case fatality ratio was 0.02%.DiscussionThe first wave of pH1N1 activity in HNE resulted in symptomatic infection in a small proportion of the population, and the number of HNE pH1N1-associated hospitalizations and deaths is likely higher than officially reported.
Highlights
On May 26, 2009, the first confirmed case of Pandemic (H1N1) 2009 virus infection in Hunter New England (HNE), New South Wales (NSW), Australia was identified
HNE is a region located in the northeast of the Australian state of New South Wales (NSW) which covers a geographic area of 130,000 square kilometers and has a population of approximately 866,000 people whose public health needs are served by Hunter New England Population Health (HNEPH) [1]
Virologic Data During May 30–August 28, 2009, 34,177 specimens were tested for influenza viruses by SEALS, Institute of Clinical Pathology and Medical Research (ICPMR), and five NSW pathology services, and of those, 7,485 (22%) were positive for influenza A virus, and 4,094 specimens (12% of all specimens tested for influenza viruses, 55% of specimens testing positive for influenza A viruses) were positive for Pandemic (H1N1) virus (pH1N1)
Summary
On May 26, 2009, the first confirmed case of Pandemic (H1N1) 2009 virus (pH1N1) infection in Hunter New England (HNE), New South Wales (NSW), Australia (population 866,000) was identified. On May 26, 2009, the first confirmed case of infection with Pandemic (H1N1) 2009 virus (pH1N1) in a resident of Hunter New England (HNE) Area Health Service, Australia was identified. Upon identification of the introduction of pH1N1 to Australia, HNEPH rapidly established multiple surveillance systems to track and determine the impact of circulation of the pandemic virus in the community. We used data from complementary surveillance systems in HNE to estimate the disease burden resulting from pH1N1 circulation and to describe the first wave of pH1N1 activity, including laboratory detection of pH1N1 virus, community influenza-like illness, hospitalizations, and deaths, over a three month period from June 1-August 30, 2009
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