Relationship Between Influenza, Temperature, and Type 1 Myocardial Infarction: An Ecological Time-Series Study

BackgroundPrevious studies investigating the relationship of influenza with acute myocardial infarction (AMI) have not distinguished between AMI types 1 and 2. Influenza and cold temperature can explain the increased incidence of AMI during winter but, because they are closely related in temperate regions, their relative contribution is unknown. Methods and ResultsThe temporal relationship between incidence rates of AMI with demonstrated culprit plaque (type 1 AMI) from the regional primary angioplasty network and influenza, adjusted for ambient temperature, was studied in Madrid region (Spain) during 5 influenza seasons (from June 2013 to June 2018). A time‐series analysis with quasi‐Poisson regression models and distributed lag‐nonlinear models was used. The incidence rate of type 1 AMI according to influenza vaccination status was also explored. A total of 8240 cases of confirmed type 1 AMI were recorded. The overall risk ratio (RR) of type 1 AMI during epidemic periods, adjusted for year, month, and temperature, was 1.23 (95% CI, 1.03–1.47). An increase of weekly influenza rate of 50 cases per 100 000 inhabitants resulted in an RR for type 1 AMI of 1.16 (95% CI, 1.09–1.23) during the same week, disappearing 1 week after. When adjusted for influenza, a decrease of 1ºC in the minimum temperature resulted in an increase of 2.5% type 1 AMI. Influenza vaccination was associated with a decreased risk of type 1 AMI in subjects aged 60 to 64 years (RR, 0.58; 95% CI, 0.47–0.71) and ≥65 years (RR, 0.53; 95% CI, 0.49–0.57). ConclusionsInfluenza and cold temperature were both independently associated with an increased risk of type 1 AMI, whereas vaccination was associated with a reduced risk among older patients.
This work has been partially funded by unrestricted research grants from the Fundación para la Investigación Biomédica, University Hospital “Príncipe de Asturias” (Servicio Madrileño de Salud, Madrid, Spain) (to Drs García‐Lledó and de Abajo) and funding from Sanofi‐Pasteur S.A., a manufacturer of influenza vaccines (to Dr de Abajo). The funders had no role in the study design, data collection, data analysis, data interpretation, or writing the report. Dr Tobías received support from the Japanese Society for the Promotion of Science in its invitation‐to‐research fellowship program in Japan (S18149).