The effect of statins on influenza-like illness morbidity and mortality

Purpose The effect of statins on cytokine-mediated inflammatory responses may impact on the prognosis of influenza. We assessed whether statin use decreases the incidence of adverse influenza-related outcomes. Additionally, we used a new-user study design to minimize healthy user bias. We further examined the possibility of non-causal associations by using unrelated outcomes. Methods We used the UK Clinical Practice Research Datalink to identify all patients aged 30 or older diagnosed with influenza-like illness during 1997–2010. Statin users were compared with propensity score-matched patients not receiving statins. The outcome was hospitalization for influenza or pneumonia or death in the 30 days following influenza diagnosis. Logistic regression estimated cumulative incidence ratios. Results The study cohort included 5181 statin users matched to 5181 non-users. The 30-day incidence of hospitalization or death was 3.5% in statin users and 5.2% in non-users, resulting in a 27% lower incidence with statin use (cumulative incidence ratio: 0.73, 95%CI: 0.59–0.89). New statin users were less protected against our composite outcome. The effect of statins was less pronounced among those with respiratory and cardiac disease. Statin use was shown to be associated with a non-statistically significant risk reduction of motor vehicle accident and burns. Conclusion The attenuation of the effect of statins with the new-user design, supporting evidence from the assessment of effect modification, and additional sub-analyses evaluating the effect of statins on non-related outcomes suggest that the beneficial effect of statins on influenza-related adverse outcomes may be explained by a healthy user bias. Copyright © 2016 John Wiley & Sons, Ltd.