• Vol. 42 No. 5, 232–236
  • 15 May 2013

Risk Factors for Complicated Influenza A (H1N1) 2009 Disease in Children



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Introduction: Singapore had its first case of pandemic influenza A (H1N1) 2009 on 26 May 2009. As of 3 August 2009, 440 children with confirmed H1N1 were admitted to KK Women’s and Children’s Hospital (KKH).

Materials and Methods: This is a retrospective case control study of children admitted from 26 May 2009 to 19 July 2009 with H1N1 infection. Cases and controls were first differentiated by whether they were complicated or non-complicated in nature, and subsequently analysed with regards to possible independent risk factors.

Results: We analysed 143 admitted children; 48 cases and 95 controls (1 : 2 ratio). Significant comorbidity was found in 20.3% (n = 29) of patients with the majority having asthma (n = 18, 12.6 %) followed by obesity (n = 7, 4.9%). Binary logistic regression analysis showed risk factors for complicated disease were comorbidity (adjusted OR 6.0, 95% CI, 2.5 to 14.6, P < 0.0001) and age <2 years (adjusted OR 9.8, 95% CI, 2.4 to 40, P = 0.001). Age less than 5 years was not found to be a risk factor.

Conclusion: In the early stages of an evolving influenza epidemic when oseltamivir stocks are low, oseltamivir treatment for influenza can be streamlined and offered to those at highest risk who are under 2 years old or have significant comorbidity to prevent complicated disease.

In March and April 2009, Mexico started experiencing an epidemic of influenza-like illness and on 17 April 2009, the novel strain of influenza A (H1N1) was identified. This virus appears to have resulted from genetic re-assortment of influenza viruses from swine, avian and human sources. As of 6 August 2009, the virus was in 6 continents, with 177,457 laboratory-confirmed cases and 1462 deaths worldwide. The first influenza A H1N1 case was detected in Singapore on 26 May 2009 in a young returning traveller
from North America.5 As of 21 July 2009, Singapore had more than 1000 confirmed cases with 1 fatality, and it had spread into the community.

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