Influenza in Outpatient ILI Case-Patients in National Hospital-Based Surveillance, Bangladesh, 2007–2008

Syeda Shegufta Ameer,Mahmudur Rahman,Salah Ud‐Din Khan ,M. A. Yushuf Sharker ,Tasnim Azim,Stephen P. Luby,Alexander Klimov ,W. Abdullah Brooks,Larisa V. Gubareva,A. S. M. Alamgir,Labib Imran Faruque,Eduardo Azziz‐Baumgartner ,Rebecca Garten ,Xinhua Xu ,Mustafizur Rahman,Stephen Lindstrom,Rashid Uz Zaman,Emily S. Gurley,Alicia M. Fry,M. J. Hossain

doi:10.1371/journal.pone.0008452

Abstract

BackgroundRecent population-based estimates in a Dhaka low-income community suggest that influenza was prevalent among children. To explore the epidemiology and seasonality of influenza throughout the country and among all age groups, we established nationally representative hospital-based surveillance necessary to guide influenza prevention and control efforts.Methodolgy/Principal FindingsWe conducted influenza-like illness and severe acute respiratory illness sentinel surveillance in 12 hospitals across Bangladesh during May 2007–December 2008. We collected specimens from 3,699 patients, 385 (10%) which were influenza positive by real time RT-PCR. Among the sample-positive patients, 192 (51%) were type A and 188 (49%) were type B. Hemagglutinin subtyping of type A viruses detected 137 (71%) A/H1 and 55 (29%) A/H3, but no A/H5 or other novel influenza strains. The frequency of influenza cases was highest among children aged under 5 years (44%), while the proportions of laboratory confirmed cases was highest among participants aged 11–15 (18%). We applied kriging, a geo-statistical technique, to explore the spatial and temporal spread of influenza and found that, during 2008, influenza was first identified in large port cities and then gradually spread to other parts of the country. We identified a distinct influenza peak during the rainy season (May–September).Conclusions/SignificanceOur surveillance data confirms that influenza is prevalent throughout Bangladesh, affecting a wide range of ages and causing considerable morbidity and hospital care. A unimodal influenza seasonality may allow Bangladesh to time annual influenza prevention messages and vaccination campaigns to reduce the national influenza burden. To scale-up such national interventions, we need to quantify the national rates of influenza and the economic burden associated with this disease through further studies.

Highlights

Influenza is a major public health concern, annually infecting 5–15% of the global population, resulting in an estimated 250,000 to 500,000 deaths per year [1,2]
We excluded the children aged less than 5 years of age from inpatient severe acute respiratory illness (SARI) surveillance because childhood pneumonia is very common among this age group and samples from these cases, of which a large proportion may have been positive for other respiratory viruses, were expected to overwhelm our laboratory throughput
These data are in agreement with recently published papers from El Salvador, Kenya, Thailand and India that demonstrated prevalent seasonal influenza epidemics in the tropics [21,22,24,25,26]

Summary

Introduction

Influenza is a major public health concern, annually infecting 5–15% of the global population, resulting in an estimated 250,000 to 500,000 deaths per year [1,2]. In the United States the proportion of the population infected with influenza ranges between 5–20% resulting in an average of 36,000 annual deaths [3,4]. The prevalence and burden of influenza are well described for the temperate countries in both the northern and southern hemispheres [4,5,6,7,8,9,10,11,12,13]. We identified a distinct influenza peak during the rainy season (May–September)

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Results

Conclusion