What are the main causes of hospital admissions over Christmas?

Winter hospital admissions

The number of people who attend hospital through A&E actually decreases in winter, but the proportion of people admitted increases. Conditions triggered or made worse by winter tend to require longer lengths of stay in hospitals, which means that hospital staff have less flexibility to manage demand.

Those most at risk to the effects of cold weather include:

• Older people.
• People with serious medical conditions, particularly respiratory conditions.
• Very young children.

Excess winter deaths

According to Nuffield Trust, moderately cold weather - when daily temperature falls below 5-8°C - directly correlates to mortality rates. Each 1°C drop below this level results in a 4% increase in death rates in England.

These risks are so significant, that the Office for National Statistics (ONS) measures excess winter mortality (EWM) every year, because "there is strong evidence that some of these winter deaths are indeed 'extra' and are related to cold temperatures and living in cold homes".

In the winter of 2019 to 2020 (December to March) an estimated 28,300 excess winter deaths (EWD) occurred in England and Wales. These were the total number of deaths compared to the average number of deaths over the rest of the year.

Cold weather plan

This is a yearly trend that has put pressure on primary care long before the effects of the COVID-19 pandemic. In fact, in 2011 the Department of Health developed its first Cold Weather Plan (CWP) in order to "avoid the adverse health effects of winter cold by raising public awareness and triggering actions by those in contact with people who are most at risk ... [which in turn] could help to reduce pressures on the health and social care system in the busiest months of the year".

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Infectious diseases

While cold weather does not directly cause infectious diseases like flu and the common cold, it does allow them to spread more easily. Exposure to cold, dry air can also affect the body's immune system and reduce its ability to fight viruses.

Flu

Flu, or influenza, is a respiratory condition caused by a viral infection. Flu infections can become life-threatening and result in hospital admissions when complications occur, such as when pneumonia develops. Flu is a leading cause of hospital admissions over winter and Christmas.

It can be difficult to tease out how many people die from flu because their deaths are often recorded as being due to the complication (pneumonia) rather than flu. However, data from England and Wales show that in 2018 and 2019, there were 29,451 and 26,342 deaths respectively where influenza and/or pneumonia were the direct cause.

COVID-19

COVID-19 is a viral infectious disease with an alarming rate of spread when people are unprotected and unvaccinated. Hospitalisations of those with severe COVID-19 symptoms have put primary care under extreme pressure, and this pressure peaks over the colder, winter months when the disease spreads more quickly.

Researchers at Imperial College London have predicted outcomes for winter 2021-2022. They believe that in the most optimistic scenario, the epidemic will remain at a similar level (to the time of study in October 2021). However, this scenario is dependent on the effectiveness of vaccinations and boosters, cross-protection, and lower contact rates.

Under pessimistic assumptions around how much contact people will have over winter, and the extent and duration of immunity provided by the above measures, researchers project a "substantial wave of total infections, hospitalisations and deaths, totalling 9,900 deaths by 31 March 2022 (from October 8th 2021)".

Respiratory diseases

Respiratory diseases affect the airways and other structures of the lungs. According to the ONS, respiratory diseases are the leading cause of excess winter mortality. During winter 2019-2020, they accounted for around 40% of all EWD in England and Wales.

Chronic lower respiratory diseases are when the airways are obstructed, and this causes shortness of breath. Colder weather puts additional strain on the heart and lungs, restricting blood flow, reducing moisture and causing inflammation, all of which can make existing respiratory problems much worse.

The major diseases are asthma and chronic obstructive pulmonary disease (COPD) - a combination of two conditions which used to be called emphysema and chronic bronchitis.

• Asthma - where the smaller airways of the lungs constrict from time to time. Winter can cause asthma flare-ups in a number of ways, including the effect of cold air on oversensitive airways, allergic reactions and the spread of infections.
• Emphysema - the air sacs in the lungs (alveoli) are damaged and the smaller surface area of the lungs means less oxygen can be absorbed into the bloodstream when you breathe.
• Chronic bronchitis - an inflammation in the tubes (bronchi) that carry air to the lungs.

According to the ONS, there were around 55% more deaths caused by chronic lower respiratory diseases in winter than the non-winter period in 2019-2020.

Pneumonia, an infection of the lungs where the air sacs fill up with fluid or pus, is also a major cause of hospitalisations over winter. In 2019-2020, there were around 68% more pneumonia-related deaths over winter compared to non-winter months.

Cardiovascular disease

Diseases that affect the heart, blood vessels, and blood flow are known as cardiovascular diseases. For people with existing conditions that affect the cardiovascular system, cold winter weather can cause blood vessels and arteries to constrict reducing blood flow, and over winter the heart is under more strain as it works harder to keep the body warm.

Many people with existing cardiovascular diseases are hospitalised over winter. These conditions have accounted for 21.1% and 20.0% of all EWD in England and Wales respectively.

• Heart failure - cold weather and viruses in winter increases the risk of heart failure, where the heart is unable to maintain adequate blood circulation.
• Heart attacks - when blood vessels constrict in reaction to the cold, the extra pressure placed on the heart can lead to a heart attack.
• Strokes - the restriction of blood vessels can raise blood pressure, and the cold helps our blood to clot, and these are major factors in strokes.

Dementia and Alzheimer's disease

Recent research has found a correlation between seasonal change from summer to winter and cognitive decline. Studies have uncovered seasonal rhythms of gene expression in the brain which can negatively affect cognition in winter.

In people who have Alzheimer's disease or dementia, this can lead to a significant decline and result in hospitalisation, and possibly to death. In terms of EWD, ONS highlighted an increase of around 15% in 2019-2020 for deaths related to Dementia and Alzheimer's disease.