Public health

Seasonality should be considered a clinical syndrome, not an epidemiological curiosity: expert


Seasonality should be considered a clinical syndrome rather than an “epidemiological curiosity”, says a leading cardiac researcher.

Presenting at the CSANZ 2018, Professor Simon Stewart, Adjunct Professor at Adelaide University and professorial research fellow at Queen Elizabeth Hospital in Adelaide, said his recent work had shown for the first time that seasonality is occurring in older Australian patients with heart disease living in five different climates.

A multi-centre retrospective study verified what had long been suspected, that ‘seasonality’ was a significant contributor to spikes in emergency admissions in hospitals leading to bed block and ramping, and not just in winter.

Seasonality is when a season-related variable causes an adverse physiological reaction, in this case triggering an unplanned hospital admission.

His pilot study reviewed data from clinical trials comprising 1500 patients (40% female and mean age 70 years) with coronary heart disease and co-morbidities who had received best-practice care after an index cardiavascular event at tertiary hospitals in Adelaide, Melbourne, Canberra, Brisbane and Sydney over an eight-year period.

The researchers found one in four patients met their definition for demonstrating “probable seasonality” – meaning they had at least four unplanned emergency admissions since their index event and 45% or more of days spent in hospital was within one season.

Seasonality was most pronounced in winter – with 10% to 20% more admissions in winter peaks than other times.

The findings strengthened the case for seasonality to be classed as a clinical syndrome, pointing to the need to rethink models of care, Professor Stewart told the limbic.

“From an epidemiological point of view and a public health point of view people accept that during winter you’ve got ambulance ramping, hospital on high alert and bed block. We have been able to establish in a retrospective way that seasonality occurs at the individual patient level.”

“We have demonstrated around two thirds of those [patients] are ‘seasonal flyers’, they come in again and again at a certain point in time due to a trigger with the seasons.”

The study found seasonality was more common in mild climates, suggesting people are less prepared to adapt to variables.

Other findings suggested that seasonality occurred in distinct sub-groups in winter, spring and summer.

Professor Stewart said his group was now developing a patient profile – with distinct sub-classifications – for what they term the “seasonal flyer”.

The “winter seasonal” has underlying respiratory condition and is susceptible to common cold and flu. The “spring seasonal” is typically triggered by sudden severe temperature changes, while the “summer seasonal” has heart failure and becomes dehydrated while following medical advice to keep fluid consumption below 1.5 litres a day.

His model also defines “seasonal flyers” as older and with multiple co-morbidities and often cognitive impairment, poorer and less educated. These factors inhibit an individual’s ability to feel the cold, dress appropriately for the weather and heat or cool their homes.

The over-arching hypothesis was that seasonality was biobehavioural, Professor Stewart said.

“There are physiological, clinical and socio-economic factors that feed into seasonality, so we need a multifaceted intervention.”

Professor Stewart said prospective studies were needed to build the case, and work was now underway both in Australia and overseas. However he believed there was already enough evidence to show seasonality was a clinical syndrome and therefore something that could be managed.

“What I am arguing is rather than think of this as an epidemiological curiosity, is to think of seasonality as a clinical syndrome that certain patients are vulnerable to.”

The phenomenon of seasonality will need to be incorporated into clinical guidelines, he suggested.

“We can manage [seasonality] better, but we need to put systems in place to prevent individuals being vulnerable to this and coming back into hospital.

“I think cardiologists would be aware of ramping, but if you look at the guidelines they follow there is no mention of seasonality. They might be eluded to things like ‘make sure your patient is vaccinated’ and the like, but there is no explicit acknowledgement that it exists and it’s a clinical entity that could be managed better.”

“This is completely new. We think this is a whole new area of research and clinical practice that will have a major impact on the burden of disease if we can find solutions.”

And while new models of care are yet to be defined, cardiologists could start to incorporate the findings into their clinical practice, he argues.

“We say to our heart failure patients, limit your fluid consumption to 1.5 L a day. But what do they do on a really hot day, or cold day, or when they go out for a walk? These are the realities facing our patients and we need to be far more flexible with the advice and treatment we give them to respond to changes in their environment.”

“Right now, there is no tried and true methods to keep them out, so at the moment it’s about awareness, maybe in thinking about the management of our patients we can do better.”

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