# (Master thesis) Influenza-associated asthma exacerbations risk

### Assessing the prevalence and exacerbations risk of influenza-associated asthma

Abstract:
The purposes of this thesis were to assess the influenza infections-induced respiratory symptoms exacerbations risk in asthmatic subjects and to estimate the influenza epidemic-associated asthma prevalence. This study presented a probabilistic risk assessment framework apprised with reported human experimental and surveillance epidemiological data.1 Experimental studies of human influenza and influenza-induced asthma data had attempted to describe the time line of viral dynamics causing health effects of human respiratory symptoms and lung function decrements. This study reanalyzed published data by using Hill based dose-response model to construct the relationship between respiratory symptoms scores (RSS) and peak expiratory flow (PEF) of lung function for experimental human influenza infection. To detect the long-term correlations of nonstationary lung function, a detrended fluctuation analysis (DFA) was applied for quantifying the correlation of the PEF time-series history. Based on the analysis, quantifying long-term correlation exponent (α) was used as a predictor of future influenza-induced asthma exacerbations. The study also employed the DFA to detect the annual long-term effect of influenza epidemic collected from the Center for Diseases Control, Taiwan during 2001–2008.2 The relationship between long-term correlation exponent of influenza epidemic and asthma admission rate was constructed to estimate the influenza-associated asthma prevalence. The results showed the respiratory symptoms scores elevation effect induced by influenza infection for both asthmatic and non-asthmatic subjects, indicating that the median exceedence risks were estimated to be 0.45 (95% confidence interval (CI): 0.12–0.82) and 0.10 (95% CI: 0.02–0.32) respectively. The DFA-based risk assessment in asthma exacerbations indicated that severe asthmatic subjects had higher influenza-associated exacerbationas risk (0.96, 95% CI: 0.88–0.99) compared with moderate (0.69, 95% CI: 0.40–0.88) and mild subjects (0.05, 95% CI: 0.01–0.13). For the quantitative fluctuation of PEF and influenza-induced asthma exacerbation risk relations, this study found that the probability of exacerbation risk can be limited to below 50% by keeping α to below 0.54. The influenza-associated asthma prevalence result found that there had significant positive association between correlation exponent influenza epidemic and asthma admission rate in Taiwan ($r^2$=0.64, p < 0.05). The median exceedence risk of asthma admission rate was estimated to be 3448 (95% CI: 3388–3508) per 100,000 population. This study could provide the new method to construct the respiratory disease patient clinical records to predict and prevent the exacerbated asthma episodes during influenza infection periods. This study could also provide a better understanding for long-term effect of influenza epidemic-associated asthma prevalence.

## Publications

. Assessing the exacerbations risk of influenza-associated chronic occupational asthma. Risk Anal., 2010.