National surveillance for influenza and influenza-like illness in Vietnam, 2006−2010
Introduction
Influenza virus infection is associated with considerable morbidity and mortality globally, including in Southeast Asian nations like Vietnam [1], [2], [3], [4], [5]. Moreover, it has been proposed that Southeast Asia may be an important region for the evolution of influenza seasonal influenza A (H3N2) virus strains that subsequently spread globally [6], [7]. Thus, influenza virologic surveillance in Southeast Asia is especially important in detecting virus strains that may need to be included in annual influenza vaccine development [6], [7]. In countries such as Vietnam, national influenza vaccine production capacity is currently being developed, so that large scale national vaccination programs may soon become more feasible in the region [8]. Epidemiological, virological, and clinical data from influenza surveillance in these countries can provide important information for policy makers on the burden of seasonal influenza and help develop prevention and control policies throughout the region. A preliminary report of the first two years of data collection of influenza surveillance in Vietnam's National Influenza Surveillance System (NISS), from 2006 to 2007, indicated that 19% of outpatients tested positive for influenza [9]. This report summarizes five years (2006–2010) of influenza surveillance among patients with influenza-like illness (ILI) seeking care at outpatient clinics in Vietnam, and describes the burden of influenza virus infection among those patients who were reported as subsequently hospitalized.
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Methods and materials
In 2006, Vietnam initiated national influenza surveillance with assistance from the World Health Organization (WHO) and the United States Centers for Disease Control and Prevention (CDC) through the creation of the National Influenza Surveillance System (NISS), as previously described [9]. NISS consists of a network of sentinel sites located in the four major regions of Vietnam. NISS is linked to regional public health laboratories, and administered by the National Institute of Hygiene and
Influenza-like illness and influenza virus infection in Vietnam
During January 1, 2006 through December 31, 2010, 326,752 persons presented for care for ILI at outpatient clinics participating in NISS; 29,804 (9.1%) were enrolled and tested for influenza. Of enrolled patients, 14,556 (49%) were female and the overall median age was 12 years (range: 1 month–94 years); 18,306 (61%) were <15 years of age (Table 1). Of enrolled patients, 13,728 (46%) patients presented to district hospitals, and 12,991 (44%) presented to surveillance sites in the Northern
Discussion
During 2006–2010 in Vietnam, influenza represented an important cause of ILI among patients presenting for medical evaluation at outpatient clinics in NISS; 22% of sampled outpatients presenting with ILI had laboratory-confirmed influenza virus infection. During this period, influenza viruses circulated throughout the year and peaks in influenza activity occurred at different periods depending upon influenza virus type or subtype. Influenza virus infection was also an important cause of
Acknowledgements
We would like to acknowledge specifically Tung Nguyen for his extremely valuable contribution. We also acknowledge all of the field and staff of the National Influenza Surveillance System network.
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