Myocardial infarction admissions were six times more likely to occur in the week after a positive test for influenza than in the year before or the 51 weeks after the infection, according to analysis of a Canadian cohort that links laboratories with administrative databases.
The investigators used this cohort data to define definitions of “risk interval” – the first 7 days after flu detection – and a combined “control interval” – 52 weeks before the flu detection and 51 weeks after the end of the risk interval.
Among the total of 364 hospital admissions for MI in patients with confirmed influenza, 20 occurred during the defined 1-week risk interval (20 admissions/week) and 344 occurred during the control interval (3.3 admissions/week), giving an incidence ratio (IR) of 6.05, Jeffrey C. Kwong, MD, of the University of Toronto and his associates reported in the New England Journal of Medicine.
There was little difference between days 1 and 3 after flu confirmation (IR, 6.3) and days 4-7 (IR, 5.8), but risk dropped off quickly after that, with IRs of 0.6 at days 8-14 and 0.75 at days 15-28. Risk was increased for older adults, those with influenza B infection, and those who had their first MI, the investigators said.
MI incidence also was elevated after infection with noninfluenza respiratory viruses, although to a lesser extent than with influenza, which suggests that “influenza is illustrative of the role that acute respiratory infections have in precipitating acute myocardial infarction,” Dr. Kwong and his associates wrote.
The study was supported by the Canadian Institutes of Health Research, by Public Health Ontario, and by the Institute for Clinical Evaluative Sciences. Dr. Kwong reported grants from Canadian Institutes of Health Research during the conduct of the study, as well as grants from Canadian Institutes of Health Research and University of Toronto.
SOURCE: Kwong JC et al. N Engl J Med. 2018. 378(4):345-53. doi: 10.1056/NEJMoa1702090.