Influenza as a trigger for cardiovascular disease: An investigation of serotype, subtype and geographic location

Background

Seasonal peaks of influenza and cardiovascular disease tend to coincide. Many excess deaths may be triggered by influenza, and the severity of this effect may vary with the virulence of the circulating influenza strain and host susceptibility. We aimed to explore the association between hospital admissions for influenza and/or pneumonia (IP) and acute myocardial infarction (AMI) or ischaemic heart disease (IHD) in Queensland, Australia, taking into account temporal and spatial variation of influenza virus type and subtype in 2007, 2008 and 2009.

Methods

This ecological study at Statistical Subdivision level (SSD, n=38) used linked patient-level data. For each study year, Standardized Morbidity Ratios (SMRs) were calculated for hospital admissions with diagnoses of IP, AMI and IHD. We investigated the associations between IP and AMI or IHD using spatial autoregressive modelling, adjusting for socio-demographic factors.
Results

Spatial autocorrelation was detected in SMRs, possibly reflecting underlying social and behavioural risk factors, but consistent with infectious disease spread. SMRs for IP were consistently predictive of SMRs for AMI and IHD when adjusted for socioeconomic status, population density and per cent Indigenous population (coefficient: 0.707, 95% confidence interval (CI): 0.318 – 1.096; 0.553, 0.222 – 0.884; 0.598, 0.307 – 0.888 and 1.017, 0.711 – 1.323; 0.650, 0.342 – 0.958; 1.031, 0.827 – 1.236) in 2007, 2008 and 2009, respectively.

Conclusions

This ecological study provides further evidence that severe respiratory infections may trigger the onset of cardiovascular events, implicating the influenza virus as a contributing factor.

Abbreviations
ABS Australian Bureau of Statistics ASGC Australian Standard Geographical Classification GDA94 Geocentric Datum of Australia with geodetic coordinates computed in 1994 NOCS Notifiable Conditions System QHAPDC Queensland Hospital Admitted Patient Data Collection SARAR spatial-autoregressive models with spatial-autoregressive errors SEIFA Socio-Economic Indexes for Areas SSD Statistical Subdivision SLA Statistical Local Area

^A Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, Level 3, 207 Bouverie Street, The University of Melbourne, Victoria 3010, Australia

^B Faculty of Science & Technology, Federation University Australia, University Drive, Mt Helen, Victoria 3350, Australia

^C Modelling and Simulation, Infection and Immunity Theme, Murdoch Childrens Research Institute, 9th floor, The Royal Children’s Hospital, 50 Flemington Road, Parkville, Victoria 3052, Australia

^D School of Mathematics and Statistics, Level 3, Old Geology South, The University of Melbourne, Victoria 3010, Australia