Ahead of Print -Influenza-Associated Hospitalizations, Singapore, 2004–2008 and 2010–2012 - Volume 20, Number 10—October 2014 - Emerging Infectious Disease journal - CDC

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Ahead of Print -Influenza-Associated Hospitalizations, Singapore, 2004–2008 and 2010–2012 - Volume 20, Number 10—October 2014 - Emerging Infectious Disease journal - CDC

Volume 20, Number 10—October 2014

Research

Influenza-Associated Hospitalizations, Singapore, 2004–2008 and 2010–2012

On This Page

• Materials and Methods
• Results
• Discussion
• Suggested Citation

Figures

• Figure 1
• Figure 2

Tables

• Table 1
• Table 2
• Table 3

Li Wei Ang , Cindy Lim, Vernon Jian Ming Lee, Stefan Ma, Wei Wei Tiong, Peng Lim Ooi, Raymond Tzer Pin Lin, Lyn James, and Jeffery Cutter

Author affiliations: Ministry of Health, Singapore (L.W. Ang, C. Lim, V.J.M. Lee, S. Ma, W.W. Tiong, P.L. Ooi, R.T.P. Lin, L. James, J. Cutter); Ministry of Defence, Singapore (V.J.M. Lee)

Suggested citation for this article

Abstract

Studies of influenza-associated hospitalizations in tropical settings are lacking. To increase understanding of the effect of influenza in Singapore, we estimated the age-specific influenza-associated hospitalizations for pneumonia and influenza during 2004–2008 and 2010–2012. The rate of hospitalization was 28.3/100,000 person-years during 2004–2008 and 29.6/100,000 person-years during 2010–2012. The age-specific influenza-associated hospitalization rates followed a J-shaped pattern: rates in persons >75 years of age and in children <6 months of age were >47 times and >26 times higher, respectively, than those for persons 25–44 years of age. Across all ages during these 2 study periods, ≈12% of the hospitalizations for pneumonia and influenza were attributable to influenza. The rates and proportions of hospitalizations for influenza, particularly among the very young and the elderly, are considerable in Singapore and highlight the importance of vaccination in protecting populations at risk.

Seasonal influenza causes a substantial burden of illness worldwide. Infections can lead to severe illness that requires hospital care and can occasionally lead to death. Several studies have documented influenza-associated hospitalizations in countries with primarily temperate climates, such as the United States (1–5), and others have documented influenza-associated hospitalizations in subtropical regions, mostly in Hong Kong, China (6–8).

In the tropics, the spread of influenza is different from that in temperate regions because of the unique tropical climate and lack of clear climatic seasons (9,10). The baseline incidence of influenza infection is high, and >1 seasonal epidemic occurs each year (11). As documented in studies on influenza-associated deaths in Singapore (9,12), the effect of influenza epidemics in the tropics is comparable to its effect in other climatic regions. However, studies on influenza-associated hospitalizations in tropical settings are lacking. Such studies can provide an understanding of the pattern of hospitalizations and severe illness that is valuable in guiding public health policies.

Laboratory testing of specimens and virologic confirmation of influenza virus infections are not typically conducted for all patients and deaths; thus, the estimation of illness attributable to influenza cannot be based on reported episodes alone. Influenza can precipitate or exacerbate other respiratory and circulatory conditions, and there is a wide spectrum of clinical pathways and outcomes for influenza-associated conditions and complications. Pneumonia was ranked fifth in the list of top 10 conditions for hospitalization in Singapore in 2012 (13). There is a need to estimate the effect of influenza on health care utilization in terms of hospitalization for pneumonia and influenza.

Singapore has a robust data collection system, which facilitates the integration of databases from virologic surveillance for influenza and hospital systems. The aim of our study was to examine the influenza-associated hospitalization rates and proportions of pneumonia and influenza hospitalizations in Singapore. Age groups spanning <6 months to ≥75 years of age were examined to further identify the populations at greatest risk for influenza-associated hospitalizations.

Ms Ang is an assistant director in the Communicable Diseases Analytics unit of the Biostatistics and Research Branch, Epidemiology and Disease Control Division, at the Ministry of Health, Singapore. Her research interests include statistical applications, disease epidemiology, and public health surveillance.

Acknowledgment

We greatly appreciate and acknowledge the contribution of staff at the public acute-care hospitals, government primary care clinics, and private general practitioner clinics involved in the virologic surveillance for influenza. We thank the Research and Strategic Planning Division of the Health Promotion Board for sharing findings from the Health Behavior Surveillance of Singapore on the proportion of adults in Singapore who reported having been vaccinated against influenza.

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Figures

• Figure 1. Weekly number of hospitalizations for pneumonia and influenza and proportion of influenza-positive specimens as determined on the basis of virologic surveillance, Singapore, 2004–2008 and 2010–2012. A) Hospitalizations and diagnostic...
• Figure 2. Age-specific rates (per100,000 person-years) and proportions of influenza-associated hospitalizations for pneumonia and influenza, Singapore. A) 2004–2008 and B) 2010–2012. Black bold lines indicate influenza-associated hospitalization rate per 100,000 person-years;...

Tables

• Table 1. Virologic surveillance for influenza in Singapore during 2 study periods, 2004–2008 and 2010–2012
• Table 2. Age-specific hospitalization rates (per 100,000 person-years) for pneumonia and influenza in Singapore during 2 study periods, 2004–2008 and 2010–2012
• Table 3. Estimated influenza-associated hospitalizations for pneumonia and influenza in Singapore during 2 study periods, 2004–2008 and 2010–2012

Suggested citation for this article: Ang LW, Lim C, Lee VJM, Ma S, Tiong WW, Ooi PL, et al. Influenza-associated hospitalizations, Singapore, 2004–2008 and 2010–2012. Emerg Infect Dis. 2014 Oct [date cited]. http://dx.doi.org/10.3201/eid2010.131768

DOI: 10.3201/eid2010.131768