Influenza, Influenza-like Symptoms and Their Association With Cardiovascular Risks
Aims: To synthesise the evidence relating influenza and influenza-like symptoms to the risks of myocardial infarction (MI), heart failure (HF) and stroke.
Methods: We conducted a systematic review and meta-analysis of the evidence relating influenza and influenza-like symptoms to the risks of MI, HF and stroke. We systematically searched all MEDLINE and EMBASE entries up to August 2014 for studies of influenza vs. the cardiovascular outcomes above. We conducted random effects meta-analysis using inverse variance method for pooled odds ratios (OR) and evaluated statistical heterogeneity using the I statistic.
Results: We identified 12 studies with a total of 84,003 participants. The pooled OR for risk of MI vs. influenza (serologically confirmed) was 1.27 (95% CI, confidence interval 0.54–2.95), I = 47%, which was significant for the only study that adjusted for confounders (OR 5.50, 95% CI 1.31–23.13). The pooled OR for risk of MI vs. influenza-like symptoms was 2.17 (95% CI 1.68–2.80), I = 0%, which was significant for both unadjusted (OR 2.23, 95% CI 1.65–3.01, five studies) and adjusted studies (OR 2.01, 95% CI 1.24–3.27, two studies). We found one study that evaluated stroke risk, one study in patients with HF, and one that evaluated mortality from MI – all of these studies suggested increased risks of events with influenza-like symptoms.
Conclusions: There is an association between influenza-like illness and cardiovascular events, but the relationship is less clear with serologically diagnosed influenza. We recommend renewed efforts to apply current clinical guidelines and maximise the uptake of annual influenza immunisation among patients with cardiovascular diseases, to decrease their risks of MI and stroke.
During a typical flu season in England and Wales, there are around 1.1 million extra consultations for acute respiratory infections, over 3000 excess hospital admissions, and around 12,500 deaths. In the H1N1 influenza pandemic, around 540,000 people in England had symptomatic H1N1 infection, with a case fatality rate of 26 deaths per 100,000 cases.
There is some observational evidence that major cardiovascular events are a prominent mechanism in deaths linked to influenza. Excess mortality during influenza epidemics in Europe and the USA in the early 1900s was indeed attributed to causes other than influenza, such as heart disease, a finding replicated in more contemporary studies. Stroke also appears to be more common after a respiratory infection.
While some studies suggests that influenza may be a precursor to incident cardiovascular events, there remain inconsistencies in the literature. Several reviews have evaluated the potential for influenza to trigger cardiovascular events. These articles have summarised cardiovascular manifestations of influenza and described the direct effects of the virus on the myocardium, as well as the potential mechanisms of acute coronary syndrome with infection.
While existing studies have shown some evidence that influenza may be associated with cardiovascular disease (CVD) there has been no published meta-analysis of the association. In addition, these studies focused on coronary heart disease, while less is known about stroke and heart failure (HF).
In view of the uncertainty regarding the association between influenza and influenza-like symptoms and risk of CVD, we conducted a systematic review and meta-analysis to quantify the risk of myocardial infarction (MI), HF and stroke among patients recorded as having influenza and influenza-like symptoms.
Abstract and Introduction
Abstract
Aims: To synthesise the evidence relating influenza and influenza-like symptoms to the risks of myocardial infarction (MI), heart failure (HF) and stroke.
Methods: We conducted a systematic review and meta-analysis of the evidence relating influenza and influenza-like symptoms to the risks of MI, HF and stroke. We systematically searched all MEDLINE and EMBASE entries up to August 2014 for studies of influenza vs. the cardiovascular outcomes above. We conducted random effects meta-analysis using inverse variance method for pooled odds ratios (OR) and evaluated statistical heterogeneity using the I statistic.
Results: We identified 12 studies with a total of 84,003 participants. The pooled OR for risk of MI vs. influenza (serologically confirmed) was 1.27 (95% CI, confidence interval 0.54–2.95), I = 47%, which was significant for the only study that adjusted for confounders (OR 5.50, 95% CI 1.31–23.13). The pooled OR for risk of MI vs. influenza-like symptoms was 2.17 (95% CI 1.68–2.80), I = 0%, which was significant for both unadjusted (OR 2.23, 95% CI 1.65–3.01, five studies) and adjusted studies (OR 2.01, 95% CI 1.24–3.27, two studies). We found one study that evaluated stroke risk, one study in patients with HF, and one that evaluated mortality from MI – all of these studies suggested increased risks of events with influenza-like symptoms.
Conclusions: There is an association between influenza-like illness and cardiovascular events, but the relationship is less clear with serologically diagnosed influenza. We recommend renewed efforts to apply current clinical guidelines and maximise the uptake of annual influenza immunisation among patients with cardiovascular diseases, to decrease their risks of MI and stroke.
Introduction
During a typical flu season in England and Wales, there are around 1.1 million extra consultations for acute respiratory infections, over 3000 excess hospital admissions, and around 12,500 deaths. In the H1N1 influenza pandemic, around 540,000 people in England had symptomatic H1N1 infection, with a case fatality rate of 26 deaths per 100,000 cases.
There is some observational evidence that major cardiovascular events are a prominent mechanism in deaths linked to influenza. Excess mortality during influenza epidemics in Europe and the USA in the early 1900s was indeed attributed to causes other than influenza, such as heart disease, a finding replicated in more contemporary studies. Stroke also appears to be more common after a respiratory infection.
While some studies suggests that influenza may be a precursor to incident cardiovascular events, there remain inconsistencies in the literature. Several reviews have evaluated the potential for influenza to trigger cardiovascular events. These articles have summarised cardiovascular manifestations of influenza and described the direct effects of the virus on the myocardium, as well as the potential mechanisms of acute coronary syndrome with infection.
While existing studies have shown some evidence that influenza may be associated with cardiovascular disease (CVD) there has been no published meta-analysis of the association. In addition, these studies focused on coronary heart disease, while less is known about stroke and heart failure (HF).
In view of the uncertainty regarding the association between influenza and influenza-like symptoms and risk of CVD, we conducted a systematic review and meta-analysis to quantify the risk of myocardial infarction (MI), HF and stroke among patients recorded as having influenza and influenza-like symptoms.
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