A new study, which appears today in the online edition of the European Heart Journal, has found strong evidence that recent respiratory infections increase the risk of heart attacks and strokes, both of which are more common in the winter.
It has for some years been recognised, using information from death certificates, that there is an excess of deaths from coronary heart disease (CHD) and stroke during the winter months, over and above those directly attributable to deaths from respiratory disease. More direct evidence has been necessary.
The authors of this study applied to the British Heart Foundation for funding to enable them to undertake further research to confirm or refute the findings of previous studies based on information from general practice which showed that respiratory infections were a strong risk factor for stroke.
The group, led by Tim Clayton and Tom Meade of the London School of Hygiene & Tropical Medicine's Medical Statistics Unit, carried out a clinical case-control study in a general practice database, the IMS Disease Analyzer Mediplus database (IMS), which is used widely in epidemiological research. It contains details of some two million patients registered with approximately 500 GPs.
They found a doubling of risk of both heart attack and stroke in the week following respiratory infection, which reduced over time so that there was little excess risk beyond one month. Risk did not depend on age or gender and for heart attack was seen at every level of preceding risk, whether this had been low or high. There was also some evidence of an association between recent urinary tract infection and subsequent heart attack or stroke.
The researchers say that the benefit of reducing respiratory infection, either through ensuring high immunisation rates or by treating and preventing infection, may be substantial.
Tim Clayton comments: 'These data add to the growing body of evidence linking respiratory infection with subsequent risk of cardiovascular events. However the absolute risk of such an event to an individual with respiratory infection remains low'.
Dr. Mike Knapton, Director of Prevention and Care at the British Heart Foundation, which funded the study, says: 'We recommend that anyone with heart disease has the flu jab. Influenza is a serious infection, particularly in patients with heart disease such as heart failure, and it could even trigger a heart attack.
''Flu is a potential killer and heart patients are offered the flu jab for free, no matter what their age. We strongly recommend they take up the offer to give themselves protection against the flu'.
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