Respiratory Infection and Cardiovascular Events Are Associated


LONDON, Dec. 6 -- For reasons that are not clear, a respiratory infection doubles the risk of a myocardial infarction or stroke within a week, according to investigators here.The strength of the associations, detected in a case-control study, decreased after the first seven days following an infection, Timothy C. Clayton, M.Sc., of the London School of Hygiene and Tropical Medicine, and colleagues reported in the December issue of the European Heart Journal. "In view of the strong evidence that respiratory infections increase the risk of MIs and strokes, it may therefore be that aborting or preventing attacks of influenza will reduce vascular events," the authors concluded.
Action Points --->
Explain to interested patients that this study suggests that the risk of myocardial infarction and stroke appears to be increased within the first week after a respiratory infection.
Point out that for an individual the increased risk is small.
Also point out the limitations of a case-control study.
"MIs and strokes occur more frequently during the winter months," they added. "Since there may be a large number of vascular deaths attributable to respiratory infection, over and above those directly attributable to respiratory disease, the benefits of reducing respiratory infection, particularly during the winter months, could be substantial."
In an interview, c-oauthor Tom W. Meade, D.M., emphasized that the association between respiratory infection and cardiovascular events poses a small risk to an individual patient, even though the population-wide risk is statistically significant.
The association between respiratory infection and MI during the first few days was first recognized a decade ago, but that study of cardiovascular events and MI excluded patients older than 75 and those with risk factors for coronary heart disease.
The current study analyzed a large general practice database, including older patients and those with coronary risks.
Investigators interrogated the database to identify all first diagnoses of MI or stroke and compared those events with patients' medical history for the preceding month. Each case was paired with a matched control.
The analysis revealed 11,155 MI cases and 9,208 stroke cases. Medical records showed that 326 MI patients had respiratory infections during the month preceding the infarction, as did 260 stroke patients.
The risk for MI or stroke was significantly increased in the first seven days following respiratory infection. Compared with the control group, infection within the preceding seven days increased the odds ratio for MI to 2.10 and the odds ratio for stroke to 1.92. The association between respiratory infection and MI occurred at all levels of underlying cardiovascular risk, the authors noted.
"Our results strengthen the evidence for a strong association between recent respiratory infection and both MI and stroke," the authors concluded. "Thus, the odds ratios for infection three days prior to the index date were 3.75 for MI and 4.07 for stroke."
In acknowledging limitations of a case-control study, Clayton and colleagues pointed out the inherent risk that control groups might not be comparable to cases. They could not rule out the possibility of missing information on some cardiovascular risk factors. They also could not rule out the possibility that risk factors they did not examine might have played a role in MI or stroke.
Despite those limitations, the authors asserted, "There is irrefutable evidence of a strong association between recent respiratory infection and MI and also of stroke."
The study was supported by the British Heart Foundation.
Clayton reported no conflicts of interest. Dr. Meade disclosed that he is a paid member of the advisory committee for the proprietary database used for the study.
Primary source: European Heart JournalSource reference:Clayton TC, et al "Recent respiratory infection and risk of cardiovascular disease: case-control study through a general practice database" Eur Heart J 2007; DOI: 10.1093/eurheartj/ehm516.