• Vol. 39 No. 4, 283–290
  • 15 April 2010

An Epidemiological Study of 1348 Cases of Pandemic H1N1 Influenza Admitted to Singapore Hospitals from July to September 2009



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Introduction: We reviewed the epidemiological features of 1348 hospitalised cases of influenza A (H1N1-2009) [pandemic H1N1] infection in Singapore reported between 15 July and 28 September 2009.

Materials and Methods: Data on the demographic and epidemiological characteristics of hospitalised patients with confirmed pandemic H1N1 infection were collected from all restructured and private hospitals in Singapore using a standard template and were analysed retrospectively.

Results: Of the 1348 cases, 92 were classified as severely ill (i.e. were admitted to an intensive care unit and/or who died). Of these severely ill cases, 50 (54.3%) required mechanical ventilation. While overall hospitalisation rates were highest in the 0 to 11 months age group, the incidence of severely ill cases was highest in patients aged 65 years and older. Fifty per cent of all hospitalised cases and 28% of all severely ill cases did not have any underlying medical conditions. The following factors were found to be independently associated with a higher likelihood of severe illness: older age and the presence of the following comorbidities: neuromuscular disorders, epilepsy and obesity.

Conclusion: Between 15 July and 28 September 2009, pandemic H1N1 infection caused significant illness requiring hospitalisation, as well as intensive care and mechanical ventilation in some cases. There were 18 deaths from pandemic H1N1 during this period, which corresponded to a case-fatality rate of 7 deaths for every 100,000 cases of pandemic H1N1.

On 17 April 2009, the US Centers for Disease Control (CDC) determined that febrile respiratory illness occurring in 2 children residing in adjacent counties in southern California was caused by a novel influenza A (H1N1) virus. The virus is thought to be a re-assortment of 4 known strains of influenza A virus subtype H1N1: one that circulates in humans, one that circulates in birds, and two endemic in pigs.

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