Abstract
BackgroundBaguio City, Philippines experienced its first influenza A(H1N1)pdm09 [A(H1)pdm09] case in May 2009. In spite of numerous reports describing the epidemiological and clinical features of A(H1)pdm09 cases, there are no studies about A(H1)pdm09 epidemiology in the Philippines, where year-round influenza activity was observed.ObjectivesWe aimed to investigate the epidemiological and clinical features of A(H1)pdm09 in pandemic and post-pandemic periods.MethodsData were collected under enhanced surveillance of influenza-like illness (ILI) and severe acute respiratory infection (SARI) from January 2009 to December 2010. RT-PCR was used to detect A(H1)pdm09, following the protocol of the United States Centers for Disease Control and Prevention. The reproduction number was computed as a simple exponential growth rate. Differences in proportional and categorical data were examined using chi-square test or Fishers’ exact test.Results and ConclusionsThe outbreak was observed from week 25 to 35 in 2009 and from week 24 to 37 in 2010. The highest proportion of cases was among children aged 5–14 years. The number of ILI outpatients was 2.3-fold higher in 2009 than in 2010, while the number of inpatients was 1.8-fold higher in 2009. No significant difference in gender was observed during the two periods. The clinical condition of all patients was generally mild and self-limiting, with only 2 mortalities among inpatients in 2009. The basic reproduction number was estimated as 1.16 in 2009 and 1.05 in 2010 in the assumption of mean generation time as 2.6 days. School children played a significant role in facilitating influenza transmission.
Highlights
Baguio City is an urbanized city located in the highland of northern Luzon, Philippines with over 298,500 inhabitants
influenza-like illness (ILI) was defined as a case with fever and cough and/or sore throat, and severe acute respiratory infection (SARI) was defined as a case having all ILI symptoms and difficulty in breathing, requiring hospital admission
RT-PCR testing was used to detect A(H1)pdm09 at the Molecular Biology Laboratory in Research Institute of Tropical Medicine (RITM) using a protocol of the United States Centers for Disease Control and Prevention [11]
Summary
Baguio City is an urbanized city located in the highland of northern Luzon, Philippines with over 298,500 inhabitants It has a population density of 5,190 persons/km. In early April 2009, the first human case of influenza A(H1N1)pdm09 [A(H1)pdm09] was identified in Mexico and the United States [2]. This virus spread rapidly to other countries. In spite of numerous reports describing the epidemiological and clinical features of A(H1)pdm cases, there are no studies about A(H1)pdm epidemiology in the Philippines, where year-round influenza activity was observed. The highest proportion of cases was among children aged 5–14 years. School children played a significant role in facilitating influenza transmission
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