Anaphylactic Shock: Main Causes and Patient Outcomes

Anaphylaxis sends thousands of people across the UK to hospital every year – due to the severity of anaphylactic shock, it always needs urgent treatment. It can even be fatal. Thankfully, due to widely available medication, it can be treated quickly, but an ambulance should always be called for people in anaphylactic shock, even after they have received or self-administered first aid. 

What is anaphylaxis?

Anaphylaxis is a serious allergic reaction. A person who is exposed to a substance to which they are severely allergic can begin to experience anaphylactic shock within minutes, although it can develop up to three hours after. This type of allergic response causes difficulty breathing, a drop in blood pressure, heart rhythm changes or any combination of these dangerous symptoms. Other symptoms can include itching, swelling and nausea. 

NICE, the National Institute for Health and Care Excellence, found in 2014 that approximately 1 in 1000 people experience anaphylactic-type reactions to their allergies. 

Hospital admissions data

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Our team at CE Safety sent a Freedom of Information request to 237 NHS Trusts, requesting data on the number of patients with anaphylactic allergic reactions who were admitted to hospital or assisted by an ambulance between 2018 and 2023. 79 NHS Trusts were able to respond, and 157 NHS Trusts were not. In some of these cases, the NHS Trusts were not able to answer as the numbers were so low that it would not be possible to anonymise the data. 

The total number of cases of anaphylaxis in the data the NHS Trusts shared with our team was 70,147. This is an approximate number given that some of the Trusts were only able to specify that there were fewer than 5 patients, in order to protect the patient’s privacy.

NHS Trusts reporting the most patients with incidents of anaphylactic shock

NHS Trust	Patients between 2018-2023
East Of England Ambulance Service NHS Trust	42,594
University Hospitals Dorset NHS Foundation Trust	7817
South Central Ambulance Service NHS Foundation Trust	1944
Whittington Health NHS Trust	1415
West Yorkshire Integrated Care Board	953

Two of the NHS Trusts with the most patients with anaphylactic shock were ambulance services, which is not surprising as the first aid advice for this condition specifies that an ambulance should be called. 

University Hospitals Dorset NHS Foundation Trust unites 3 different hospitals under a single umbrella organisation, which explains why there are so many cases of anaphylaxis recorded. This NHS Trust serves a population on the south coast of England of approximately 800,000 people. Whittington Health NHS Trust serves 3 London hospitals and 16 clinics. 

West Yorkshire Integrated Care Board is a partnership between NHS, local authority, community and voluntary sector organisations and independent care providers across the cities and towns of West Yorkshire. 

Deaths data 

The FOI data we received revealed that of those NHS Trusts who were able to answer this question, the majority either reported fewer than 5 deaths in the last 5 years, or zero deaths. While very dangerous, it is plain to see that this condition is easily treatable as long as the patient is treated quickly. 

A 2021 study by Imperial College London found that hospitalisations for anaphylactic food reactions had increased between 1998 and 2018 by 5.7% a year. However, the number of fatalities compared to hospital admissions had actually dropped from 0.7% in 1998 to 0.3% in 2018. 

Causes of anaphylaxis 

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According to the information received through our FOIs, the two most common causes of anaphylactic shock between 2018 and 2023 were allergic reactions to foods, and allergic reactions to medication or medical equipment. 

There are also several less common causes for patients’ anaphylactic reactions which hospitals have recorded. These include stings or bites from insects or other animals, which is still a relatively common cause. Hospitals also found that some cases were caused by a rare reaction during blood transfusion, when the patient is sensitive to antigens contained in the donated blood. Anaphylaxis can also, rarely, be brought on by exercise. In many cases, the data provided by the NHS Trusts shows that the cause of anaphylaxis is not specified. 

Lewisham and Greenwich NHS Trust’s data from 2017 to 2023 shows that food was the main cause of most patients’ allergic reaction, followed by medicine, then insects – but the majority of cases were of an unspecified cause. 

Cause	Number of patients
Food	42
Insect	6
Medicine	14
Other	1
Unknown	601

The Royal Free London NHS Foundation Trust broke down their data from 2018-2022 as follows, with most patients suffering an allergic reaction to food, followed by medicine (apart from those whose reaction’s cause was unspecified).

Cause	Number of patients
Adverse effect of correct drug or medicament	67
Adverse food reaction	154
Unspecified	131

Many of the Trusts used different time periods or did not share the cause of the anaphylaxis in the same way as each other, or at all. This meant that it was not possible to create an accurate overall summary of the most frequently recorded cause of anaphylaxis.

Asthma sufferers more likely to experience anaphylaxis

People with asthma are more at risk of experiencing anaphylaxis. One of the most common types of asthma is allergic asthma, in which the condition’s symptoms are triggered by inhaling an allergen, such as mould or pollen. Those with this particular type of asthma are more likely to have allergies to other substances.

Children at risk 

Statistics show that children can be more likely than other age groups to be admitted to hospital suffering from anaphylactic shock. One of the reasons why this is the case could be that their allergies were previously unknown before they experienced their first severe reaction. 

The total number of confirmed cases of anaphylaxis in people aged 19 and younger was  18804 – this is 26.8% of the total confirmed cases. This does not account for young people whose ages were not shared by the NHS Trusts in order to protect patient privacy. 

East of England Ambulance Service NHS Trust data revealed that between 2019 and 2023, each year there were hundreds more under 18 year olds needing medical treatment for anaphylactic shock than there were 25-34 year olds. 

Age	2019	2020	2021	2022	2023
0-18	1311	1224	1479	1088	1069
25-34	822	767	935	734	631

While the connection between asthma and anaphylaxis has been discussed, eczema, another condition of the immune system, can also be an indicator that a child is at increased risk of allergies, which could be severe. 

It is important to educate small children about the dangers of food allergies in particular, as in group settings like schools and nurseries they might be exposed to allergens. Increasing numbers of schools now restrict common allergens such as nuts. 

Which foods are most likely to cause anaphylactic shock?

• Celery
• Cereals containing gluten
• Crustaceans
• Eggs
• Fish
• Milk
• Molluscs
• Peanuts
• Soybeans
• Tree nuts (such as hazelnuts and almonds)

Peanuts are especially notorious for causing anaphylactic reactions, and for causing reactions that occur very rapidly. Medical professionals are not yet sure why this could be. Other food allergies can include specific fruits or vegetables, such as tomatoes, strawberries and peaches. 

Allergy sufferers do not necessarily have to eat the allergen in order to have a reaction – people with very strong allergic reactions can experience airborne allergies, but luckily anaphylactic reactions to airborne allergens are rare. 

Which medicines are most likely to cause anaphylactic shock?

• Anticonvulsants
• Chemotherapy drugs
• Monoclonal antibodies (MABs)
• NSAIDs such as aspirin and ibuprofen
• Penicillin and other antibiotics

Monoclonal antibodies or MABs are a type of immunotherapy drug designed to stimulate the immune system to attack cancer cells.

NSAIDs, non-steroidal anti-inflammatory drugs, are a type of painkiller. People with an allergy to these painkillers will find that they should still be able to safely use paracetamol. 

Many people discover that they are allergic to materials used in a medical setting, such as latex, or the common antiseptic chlorhexidine. This is just one of many reasons why doctors’ notes are so important, protecting patients from being exposed to a known allergen.

First aid

The steps are the same, whether the first aid is self-administered or to help another person. 

1. The patient should lie down
2. Inject their upper thigh with adrenaline auto-injector (through clothes)
3. Phone ambulance
4. If patient’s condition has not changed, give second injection 5 to 15 minutes later
5. If asthmatic, the patient should use their blue asthma inhaler for immediate breathing relief 
6. Stay lying down while waiting for the ambulance to arrive 

If assisting someone else who is unconscious, they should be placed in the recovery position. 

Adrenaline auto-injectors 

There are three main types of adrenaline auto-injector: EpiPen®, Jext® and Emerade®. Each has a slightly different mechanism, but they share basic similarities in that they each contain a single dose of epinephrine, the drug that can stop anaphylaxis.

Each device should be held against the outer thigh at a 90 degree angle. The needle is strong enough to go through clothes to ensure it’s quick and easy for patients to use, even in public. People who are prescribed an auto-injector are advised to carry a spare – the first aid instructions for each device specify that patients whose condition does not change after the first dose should be given a second injection 5 to 15 minutes later. 

EpiPen®’s, one of the most common auto-injectors, are yellow with a blue cap and are available in two doses, 150mcg for children and patients below 30 kg in weight, and 300 mcg for most adults. To use an EpiPen®, first remove the blue safety cap, then hold it 10cm away from the upper thigh. Jab it into the upper thigh at a right angle and hold for 3 seconds. 

Jext® brand auto-injectors have a yellow cap and a black tip. This type of auto-injector is also available in the same two strengths – 150mcg and 300mcg. To use a Jext® auto-injector, remove the yellow safety cap. Push the black injector tip firmly against the outer thigh until you hear a ‘click’, then hold in place for 10 seconds. Massage the injection site. 

Emerade® auto-injectors are entirely white, and come in 150mcg, 300mcg or 500mcg doses. To use an Emerade®, remove the needle shield. Press the auto-injector against the outer thigh and hold for 5 seconds. Then, massage the injection site. 

In conclusion

Look out for the symptoms of anaphylaxis in your family, coworkers and friends. If a person is experiencing multiple symptoms across their body, or symptoms like shortness of breath, dizziness, and feeling sick, ask them if they have an auto-injector and help them use it if need be. 

Methodology

A Freedom of Information request was sent to 237 NHS Trusts around the UK. Some provided total figures across 2018-2023 of how many patients were documented with anaphylactic reactions, while others split this down into year-by-year data. Some of the NHS Trusts were able to provide data split by age and by gender. Incidents where the data indicated that there were fewer than 5 patients in a certain category, but did not specify a number, were not counted. 

Sources

FOI data sourced by CE Safety