Influenza and Flu-like Illness

We have selected the following expert medical opinion based on its clarity, reliability and accuracy. Credits: Sourced from the website Patient UK, authored by Dr Hayley Willacy (see below). Please refer to your own medical practitioner for a final perspective, assessment or evaluation.

Overview

Many viruses can cause a flu-like illness. There is usually a seasonal outbreak of flu (influenza) each winter. Flu-like illnesses typically cause a high temperature, aches and pains in muscles and joints, a cough and various other symptoms.

What is influenza?

Flu (influenza) is caused by the influenza virus. However, many other viruses can cause an illness similar to flu. It is often difficult to say exactly which virus is causing the illness, so doctors often diagnose a flu-like illness.

There are three types of influenza virus - A, B and C.

Influenza A and B cause most of the cases of flu. Each winter a different type of influenza virus causes an outbreak of flu which affects many people. This is called seasonal flu. If you get a flu-like illness during an outbreak of seasonal flu, it is likely to be caused by the prevailing influenza virus. Most cases of flu usually occur in a period of six to eight weeks during the winter.

Swine flu is caused by a particular strain of influenza A virus which is called H1N1v. It seems to affect children and young adults more commonly than those over the age of 60 years. Most people with this type of flu have a mild flu-like illness. You are more likely to have sickness and/or diarrhoea with this type of flu.

Note: bird flu (avian influenza) is different and is more serious.

Flu symptoms

Common flu symptoms in adults and older children include:

• High temperature (fever)
• Sweats
• Aches and pains in muscles and joints
• A dry cough
• Sore throat
• Sneazing
• Headache
• Feeling sick (nausea)
  
  

The illness caused by the influenza virus tends to be worse than illnesses caused by other viruses which cause a flu-like illness. Even if you are young and fit, flu can make you ill enough to need to go to bed.

Common flu symptoms in babies and young children include fever, sweats, a cough, sore throat, sneezing, difficulty in breathing, lack of energy (lethargy) and poor feeding. Some young children with flu may have a febrile convulsion. A febrile convulsion is a fit that occurs in some children with a fever.

Typically, symptoms are at their worst after 1-2 days. Then they usually gradually ease over several days. An irritating cough may persist for a week or so after other symptoms have gone. Most people recover completely within 2-7 days.

How do you catch flu?

Flu is passed from person to person by droplets created when someone with the infection sneezes or coughs. You can also catch it by touching a surface where the virus has been deposited. Flu can spread quickly in these ways.

Serious illnesses that are similar to flu

Other serious illnesses can have similar symptoms to flu (influenza) when they first develop - for example, meningitis, malaria, or pneumonia. If you have a more serious illness, other symptoms usually develop in addition to those mentioned above.

Symptoms to look out for which may mean that you have a different and more severe illness include:

• Rash - in particular if dark red spots develop that do not fade when pressed.
• Stiff neck - particularly if you cannot bend your neck forward.
• A headache that becomes worse and worse.
• Dislike of bright lights - if you need to shut your eyes and turn away from the light.
• Drowsiness and/or confusion.
• Repeatedly being sick (vomiting).
• Chest pains.
• Coughing up blood or blood-stained phlegm (sputum).
  
  

Note: it is important to tell a doctor if you have flu-like symptoms and you have been to a country within the previous year where malaria is present. Initial symptoms of malaria can be similar to flu.

Flu treatment

Your immune system will usually clear viruses that cause flu (influenza) and flu-like illnesses. Treatment aims to ease symptoms until the infection goes, and to prevent complications. There are several treatment options as outlined below.
 

General measures

Stay at home as much as possible to prevent passing on the infection.

Paracetamol and/or ibuprofen can lower your temperature and also ease aches and pains. Drink plenty of fluids to prevent lack of fluid in the body (dehydration). It is best not to smoke. Decongestant drops, throat lozenges and saline nasal drops may be helpful to ease nose and throat symptoms.

Note: parents and carers should not use over-the-counter cough and cold medicines in children under 6 years old. There is no evidence that they work and they can cause side-effects such as allergic reactions, effects on sleep, or even hallucinations.

Antiviral medicines

Antiviral medicines called oseltamivir (trade name Tamiflu®) and zanamivir (trade name Relenza®) are sometimes used. Antiviral medicines do not kill the virus but interfere with the way the virus multiplies.

Antiviral medicines do not cure flu or offer long-term protection against flu. If you do not have an antiviral medicine, you are still likely to make a full recovery. However, antiviral medicines may reduce the risk of developing complications. They may also reduce the severity and duration of symptoms by a day or two.

An antiviral medicine may be prescribed if you are at increased risk of developing complications when you have flu (see list below). Treatment is usually taken for five days.

Antiviral medicines should be given within 48 hours of getting the flu (within 36 hours for zanamivir in children) or of having contact with someone who has the flu. This is because the sooner they are given, the better they work.

Antibiotic medicines

Antibiotics kill germs called bacteria, but not viruses. Therefore, they are not routinely prescribed for viral illnesses such as flu or flu-like illnesses. However, they may be used if a complication develops like a chest infection caused by a germ (bacterium) or pneumonia (see below).

Admission to hospital

A small number of people with flu become ill enough to need hospital admission. This is usually because they have developed complications from flu.

Complications of flu

If you are normally well then you are unlikely to develop complications. You are likely to recover fully. However, see a doctor if symptoms change or become worse. Complications are more likely to develop if you are in any of the at-risk groups listed below.

The most common complication is a chest infection caused by a germ (bacterium). This may develop in addition to the viral infection (that is, a secondary infection). This can sometimes become serious and develop into pneumonia. A course of antibiotic medication will often cure this. However, a bacterial infection can sometimes become life-threatening, particularly in those who are frail or elderly.

Note: with flu (influenza) or a flu-like illness it is common to have a cough that lingers for 1-2 weeks after other symptoms have gone. Green phlegm (sputum) does not necessarily mean that you have a secondary chest infection.

The symptoms to look out for that may indicate a secondary chest infection include:

• A recurrence of a high temperature (fever).
• Worsening of cough.
• Shortness of breath.
• Fast breathing.
• Chest pain.
  
  

Other complications that sometimes occur include a sinus infection and an ear infection. Other serious complications are rare, such as brain inflammation (encephalitis).

Immunisation for Flu

Flu Jab

Flu jabs do not prevent other viral infections which can cause coughs and colds, just the particular flu virus that is expected in the coming winter.

Immunisation against seasonal flu

Flu immunisation (the flu jab) gives protection against seasonal flu and lasts for one year. If 10 people have the flu jab, it usually provides protection from flu for 7 or 8 of them. If the vaccine does not match the predicted flu types around that year, the protection rate can be lower. For example, in winter 2015/2016 the vaccine protected between 5-6 elderly people out of 10.

The immunisation is normally given in autumn each year. The flu injection is made from the three strains of flu virus that are most likely to cause outbreaks in the coming winter. Each year these are slightly different, so a new jab needs to be made every year. You need a yearly jab to stay protected.

The World Health Organization (WHO) monitors influenza viruses throughout the world and recommends which strains are to be included in the current year's vaccine.

For the 2017/18 flu season in the UK it is recommended that vaccines contain the following three strains:

• An A/Michigan/45/2015 (H1N1)pdm09-like virus.
• An A/Hong Kong/4801/2014 (H3N2)-like virus.
• A B/Brisbane/60/2008-like virus.

Vaccines containing four strains (quadrivalent) should contain the above three viruses and a B/Phuket/3073/2013-like virus.

The adult immunisation does not actually contain any living flu virus. This means that it cannot cause flu or any other infections. If you develop a cough or cold shortly after having a flu immunisation it is a coincidence.

Who should be immunised against the seasonal flu virus?

Seasonal flu is the particular type of flu virus that arrives in the UK each autumn. The actual type varies from year to year. The new jab is developed each year to protect against the expected type. The flu jab takes up to 14 days for full protection after having the jab.

The Department of Health issues advice as to who should be immunised. This is reviewed from time to time. The aim is to protect people who are more likely to develop complications from flu.

Current advice is that you should be immunised against the seasonal flu virus each autumn if you:

• Are aged 65 or over.
• Have any ongoing (chronic) lung diseases.
• Examples include chronic bronchitis, emphysema, cystic fibrosis and severe asthma (needing regular steroid inhalers or tablets). It is also recommended for any child who has previously been admitted to hospital with a chest infection.
• Have a chronic heart disease. Examples include angina, heart failure or if you have ever had a heart attack.
• Have a serious kidney disease.Examples include nephrotic syndrome, chronic kidney disease, a kidney transplant.
• Have a serious liver disease such as cirrhosis.
• Have diabetes.
• Have a poor immune system.
• Examples include if you are receiving chemotherapy or steroid treatment (for more than a month), if you have HIV/AIDS or if you have had your spleen removed.
• Have certain serious diseases of the nervous system such as multiple sclerosis or have had a stroke in the past.
• Live in a nursing home or other long-stay residential care accommodation.

In addition to the main at-risk groups of people listed above:

• You should be immunised if you are the main carer for an elderly or disabled person whose welfare may be at risk if you fall ill with flu.
• Staff involved in direct patient care (including nursing and care homes) may be offered a flu jab by their employer.
• Pregnant women. Even if you are otherwise healthy it is now recommended that all pregnant women receive the flu jab.
• If you are healthy and an adult aged under 65 years and you do not fall into any of the above categories, then you do not need immunisation against seasonal flu. This is because you are unlikely to develop complications from flu.

Seasonal flu jab side-effects

Immunisation against seasonal influenza (the flu jab) usually causes no problems. You may have a temporary mild soreness at the injection site. Sometimes, it can cause a mild raised temperature (fever) and slight muscle aches for a day or so. This soon settles and does not lead to flu or other problems.

Serious reactions have been reported but are rare. For example, a severe allergic reaction, inflammation of nerves and inflammation of the brain (encephalitis) are very rare reactions.

Who should not have the seasonal flu jab?

The vast majority of people can receive flu immunisation (the flu jab).

However, the following groups of people should not be immunised with the usual vaccine:

• Those who have a severe allergy to eggs. However, you can still receive a different immunisation that protects against the swine flu strain (H1N1v). There is also egg-free vaccine - see below.
• Those who have had a previous allergic reaction to a flu virus immunisation in the past.
• Although most flu vaccines are grown in hens' eggs, an egg-free vaccine is available and can be given. People with a history of severe egg allergy can be given the egg-free vaccine.
• Children who do not have a good working immune system should not be given the live flu vaccine. This includes children with leukaemia or HIV. Children who live with, or have close contact with, someone who has a poorly working immune system should also not be given the live vaccine. However, children who do not have a good working immune system and children who live with, or have close contact with, someone who has a poorly working immune system can be given the inactivated vaccine.
  
  

Flu immunisation can be given at the same time as other immunisation; it is often given at the same time as the pneumonia immunisation. It is also safe to be given if you are either pregnant or breast-feeding.

Where can I have the flu jab?

You can be given your flu jab from one of the following:

• Your GP surgery.
• Your local pharmacy (if they offer this service).

About the Author 

Dr Hayley Willacy

MB ChB, FRCGP, DFSRH, PgCert MEd Ed

Dr Hayley Willacy is a GP and Fellow of the Royal College of General Practitioners who lives in Cumbria. After authoring for EMIS (patient.info) for several years she became Clinical Editor in November 2012. Her particular interests are maternity, child health, family planning, sexual health, chronic neurological disorders, mental health and intellectual disability. She was partly trained as a gynaecologist before moving into primary care, where she was initially a full-time partner in Coventry. She tutors undergraduates from Lancaster University medical school and is an FY2 supervisor. She designed and produced the Education section for patient.info and has published several clinical articles in peer-reviewed journals.

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