Incidence, seasonality and mortality associated with influenza pneumonia in Thailand: 2005-2008.

James Mark Simmerman,Sonja J Olsen,Malinee Chittaganpitch,Peera Areerat,Kumnuan Ungchusak,Somrak Chantra,Henry C Baggett,Alicia Fry,Supamit Chunsuttiwat,Susan Maloney,Jens Levy,Timothy Uyeki,Somsak Thamthitiwat,Landon Myer

doi:10.1371/journal.pone.0007776

James Mark Simmerman, Sonja J Olsen + Show 12 more

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https://doi.org/10.1371/journal.pone.0007776

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Abstract

BackgroundData on the incidence, seasonality and mortality associated with influenza in subtropical low and middle income countries are limited. Prospective data from multiple years are needed to develop vaccine policy and treatment guidelines, and improve pandemic preparedness.MethodsDuring January 2005 through December 2008, we used an active, population-based surveillance system to prospectively identify hospitalized pneumonia cases with influenza confirmed by reverse transcriptase–polymerase chain reaction or cell culture in 20 hospitals in two provinces in Thailand. Age-specific incidence was calculated and extrapolated to estimate national annual influenza pneumonia hospital admissions and in-hospital deaths.ResultsInfluenza was identified in 1,346 (10.4%) of pneumonia patients of all ages, and 10 influenza pneumonia patients died while in the hospital. 702 (52%) influenza pneumonia patients were less than 15 years of age. The average annual incidence of influenza pneumonia was greatest in children less than 5 years of age (236 per 100,000) and in those age 75 or older (375 per 100,000). During 2005, 2006 and 2008 influenza A virus detection among pneumonia cases peaked during June through October. In 2007 a sharp increase was observed during the months of January through April. Influenza B virus infections did not demonstrate a consistent seasonal pattern. Influenza pneumonia incidence was high in 2005, a year when influenza A(H3N2) subtype virus strains predominated, low in 2006 when A(H1N1) viruses were more common, moderate in 2007 when H3N2 and influenza B co-predominated, and high again in 2008 when influenza B viruses were most common. During 2005–2008, influenza pneumonia resulted in an estimated annual average 36,413 hospital admissions and 322 in-hospital pneumonia deaths in Thailand.ConclusionInfluenza virus infection is an important cause of hospitalized pneumonia in Thailand. Young children and the elderly are most affected and in-hospital deaths are more common than previously appreciated. Influenza occurs year-round and tends to follow a bimodal seasonal pattern with substantial variability. The disease burden varies significantly from year to year. Our findings support a recent Thailand Ministry of Public Health (MOPH) decision to extend annual influenza vaccination to older adults and suggest that children should also be targeted for routine vaccination.

Highlights

Influenza is a common vaccine preventable viral infection that can cause severe or fatal disease in the elderly, the very young and those with underlying illness [1,2,3,4,5]
Seasonality and in-hospital mortality associated with hospitalized influenza pneumonia from two provinces in Thailand during four consecutive years and extrapolate our findings to provide national estimates of disease burden
We prospectively identified all hospitalized pneumonia patients during January 2005 through December 2008 using an active, population-based surveillance system carried out through collaboration between the Thailand Ministry of Public Health (MOPH) and the U.S Centers for Disease Control and Prevention (CDC) in Sa Kaeo province in eastern Thailand and Nakhon Phanom province in northeast Thailand (Figure 1)[21,22]

Summary

Introduction

Influenza is a common vaccine preventable viral infection that can cause severe or fatal disease in the elderly, the very young and those with underlying illness [1,2,3,4,5]. Much less is known about the burden of influenza morbidity and mortality in tropical and subtropical countries [8,9]. The contribution of influenza virus infection to pneumonia, the leading cause of pediatric mortality, has not been determined. This question is important for developing countries in tropical and subtropical climates where most childhood pneumonia occurs and where influenza has historically been perceived as a mild or uncommon disease. Prospective, multi-year, populationbased data on laboratory-confirmed influenza infection are needed to describe the disease burden and inform prevention and control strategies during both interpandemic and pandemic periods. Prospective data from multiple years are needed to develop vaccine policy and treatment guidelines, and improve pandemic preparedness

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