Modeling the seasonal dynamics of influenza-associated morbidity in Taiwan
Date Issued
2009
Date
2009
Author(s)
Chang, Szu-Yuan
Abstract
Influenza virus is a major viral respiratory pathogen that can cause severe illness. The annual epidemics are thought to result in between three and five million cases of severe illness and between 250,000 and 500,000 deaths every year around the world. In temperate regions, there are clear seasonal variations in the occurrence of influenza, nonetheless, seasonality is less defined in tropical regions. The purpose of this study was to assess the impact of influenza on morbidity and seasonal dynamical behavior accounted for influenza A/H3N2-contributed influenza-like illness (ILI) in subtropical Taiwan. This study employed a Poisson seasonal regression model to fit weekly influenza-associated morbidity collected from the Center for Diseases Control, Taiwan (Taiwan CDC) during 1999 to 2007. The proposed models allow this study to adjusting influenza-associated morbidity for independent variables as annual trend, seasonality, temperature, relative humidity, viral circulation such as influenza A/H1N1, A/H3N2, type B, and respiratory syncytial virus (RSV). This study also employed a seasonally forced susceptible-infectious-recovery-susceptible (SIRS) model incorporated with sinusoidal forcing to examine the seasonality and epidemic dynamics including season-specific basic reproduction number (R0). A phase plane diagram was used to investigate the seasonal dynamics and critical threshold that regulate the influenza recurrent epidemics. The results indicate that there are stronger association between influenza-associated morbidity and temperature than that of relative humidity. Influenza A/H3N2 was the predominant virus subtype during the study period and had a nearly 50% contribution followed by type B (39%) and A/H1N1 (11%) on influenza-associated morbidity. The proposed epidemiological model demonstrated that seasonality produces mild amplitude epidemics, which the estimated intrinsic period of oscillation was approximated to one year. This study showed that the local minimum number of susceptibles (S0=0.30) was higher than that of theoretical critical threshold level (Sc=0.015), implicating there was an epidemic outbreak in the following year. This study provided a better understanding of Poisson regression modeled influenza burden guideline, seasonal A/H3N2-contributed ILI dynamics, and used the critical threshold level to predict the occurrence of subsequent epidemic or skip in subtropical Taiwan.
Subjects
Influenza
Morbidity
Seasonal dynamics
Transmission rate
Taiwan
Subtropics
Susceptible-Infectious-Recovery-Susceptible (SIRS) model
Type
thesis
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