Abstract
Many studies have found that cardiovascular deaths mostly occur within a few days of exposure to heat, whereas cold-related deaths can occur up to 30 days after exposure. We investigated whether influenza infection could explain the delayed cold effects on ischemic heart diseases (IHD) as they can trigger IHD. We hypothesized two pathways between cold exposure and IHD: a direct pathway and an indirect pathway through influenza infection. We created a multi-state model of the pathways and simulated incidence data to examine the observed delayed patterns in cases. We conducted cross-correlation and time series analysis with Japanese daily pneumonia and influenza (P&I) mortality data to help validate our model. Simulations showed the IHD incidence through the direct pathway occurred mostly within 10 days, while IHD through influenza infection peaked at 4–6 days, followed by delayed incidences of up to 20–30 days. In the mortality data from Japan, P&I lagged IHD in cross-correlations. Time series analysis showed strong delayed cold effects in the older population. There was also a strong delay on intense days of influenza which was more noticeable in the older population. Influenza can therefore be a plausible explanation for the delayed association between cold exposure and cardiovascular mortality.
Highlights
Both extreme high and low temperatures increase the risk of cardiovascular diseases (CVD), but there is a marked difference in how quickly the events occur
The interaction analysis in time series models showed that the effect the effect of extreme cold temperature on ischemic heart disease (IHD) deaths during intense influenza days was more of extreme cold temperature on IHD deaths during intense influenza days was more delayed than delayed than non-intense days
Given the consistent results, our study highlights the potential role of influenza infections in the delayed cold effect due to secondary IHD
Summary
Both extreme high and low temperatures increase the risk of cardiovascular diseases (CVD), but there is a marked difference in how quickly the events occur. The impacts of extreme heat occur quickly (1–2 days), whereas the impacts of cold usually remain for up to a month [1,2]. Though many studies have reported these distinct differences, the cause of the difference has not been investigated in detail. A study reported a risk reduction in IHD after influenza vaccination in a high risk population [7]. The idea has raised questions because the highest CVD mortality occurs within a few days of cold exposure, but this is not long enough for respiratory infections to develop [8]
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