Elsevier

Vaccine

Volume 31, Issue 40, 13 September 2013, Pages 4368-4374
Vaccine

National surveillance for influenza and influenza-like illness in Vietnam, 2006−2010

https://doi.org/10.1016/j.vaccine.2013.07.018Get rights and content

Highlights

  • During 2006–2010 in Vietnam, influenza viruses co-circulated most years and often peaked multiple times each year.

  • 22% of patients with ILI enrolled in the National Influenza Surveillance System (NISS) in Vietnam were influenza positive.

  • 9.3% of ILI patients in NISS in Vietnam were reported as subsequently hospitalized, of which 19% were influenza positive.

  • NISS suggests influenza is an important cause of ILI and reported subsequent hospitalization among outpatients in Vietnam.

Abstract

Influenza virus infections result in considerable morbidity and mortality both in the temperate and tropical world. Influenza surveillance over multiple years is important to determine the impact and epidemiology of influenza and to develop a national vaccine policy, especially in countries developing influenza vaccine manufacturing capacity, such as Vietnam. We conducted surveillance of influenza and influenza-like illness in Vietnam through the National Influenza Surveillance System during 2006–2010. At 15 sentinel sites, the first two patients presenting each weekday with influenza-like illness (ILI), defined as fever and cough and/or sore throat with illness onset within 3 days, were enrolled and throat specimens were collected and tested for influenza virus type and influenza A subtype by RT-PCR. De-identified demographic and provider reported subsequent hospitalization information was collected on each patient. Each site also collected information on the total number of patients with influenza-like illness evaluated per week. Of 29,804 enrolled patients presenting with influenza-like illness, 6516 (22%) were influenza positive. Of enrolled patients, 2737 (9.3%) were reported as subsequently hospitalized; of the 2737, 527 (19%) were influenza positive. Across all age groups with ILI, school-aged children had the highest percent of influenza infection (29%) and the highest percent of subsequent hospitalizations associated with influenza infection (28%). Influenza viruses co-circulated throughout most years in Vietnam during 2006–2010 and often reached peak levels multiple times during a year, when >20% of tests were influenza positive. Influenza is an important cause of all influenza-like illness and provider reported subsequent hospitalization among outpatients in Vietnam, especially among school-aged children. These findings may have important implications for influenza vaccine policy in Vietnam.

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.

Section snippets

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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