Flu: symptoms, course of illness and treatment

When you have aching limbs, a bad headache and a high temperature, you’re likely to lie in bed wondering whether it’s “just” a cold or if you’ve caught the flu. Some symptoms are the same with both illnesses. However, it’s worth taking a closer look to speed up your recovery, prevent complications and, above all, avoid infecting other people.      

Flu: definition and cause

How can you tell which type of virus you’re suffering from? Flu is a viral infection that is particularly common during colder months. It is caused by influenza viruses. And there are three types: A, B and C.

These viruses infect the respiratory tract and destroy the cells of the mucous membrane. They can also reach the lungs and damage the tissue there. Our body reacts to the harmful action of these intruders by ramping up the defences of its immune system. This causes inflammation in the body, which in turn causes familiar symptoms such as fever, coughing, headaches and aching limbs.

Once you’ve had the flu, your body is immune to this particular influenza virus, but as there are many variants and subgroups of types A, B and C, there is a high probability that you will catch the flu again.

Transmission and incubation period

The flu is highly contagious. The influenza viruses are transferred from person to person - via droplets in the air. This means that you catch a few tiny droplets of the virus when a sick person coughs and sneezes next to you, spreading the virus in the air.

However, the viruses can also be transmitted via smear infection, which is when we touch surfaces or objects contaminated with the virus and then touch our mouth or nose with our hands. Viruses can survive much longer than usual on surfaces such as plastic or steel, lurking there for hours or even several days.

Risk of infection is generally very high where many people come together in closed rooms, for example on public transport, in offices or at large events.

After infection, it usually takes one or two days for the illness to break out. So, the person affected is usually already contagious one day before they experience symptoms. The risk of infection is usually between four and five days after the first symptoms appear.

You are more contagious at the start of the infection, as the viral load is often higher than later in the course of the flu. People who are very seriously ill or have to take immunosuppressants due to an illness are often infectious for longer. Studies have also shown that people with chronic illnesses and severe flu excrete viruses for an average of seven days – and are therefore contagious.

Flu symptoms

The most common symptoms include a sore throat, fever, coughing, aching muscles and limbs, and a headache. These symptoms can also occur with a cold. The common cold is a flu-like infection that is also caused by viruses. Today, over 200 different cold viruses are known. Very often, these are rhinoviruses.

As the diversity of these pathogens is so great, our immune system can’t build up lasting protection against colds. However, the symptoms of a cold are usually less severe than those of the flu. Influenza usually hits us much harder, with the following symptoms:

• Sudden fever
• Dry cough or sore throat
• Aching muscles and limbs
• Severe headache 

Those affected often feel very weak, sweat profusely and have a runny nose. However, the Robert Koch Institute explains that symptoms can vary from person to person, with around a third of patients suffering fever and typical symptoms, while another third have milder, often cold-like symptoms without fever, and a final third showing no symptoms at all.

Older people or people with a weak immune system in particular often don’t have a fever, as their immune system is weakened and the body is therefore less able to fight the viruses.

Flu symptoms in children

Particularly with children, the flu can lead to gastrointestinal complaints, such as nausea, vomiting or diarrhoea.

Flu or cold: what are the differences?

Stages of the flu

Most people who catch the flu are struck down straight away. Symptoms such as a high temperature, sore throat, headache and aching limbs appear quickly and can worsen rapidly. Coughing and a runny nose tend to develop more slowly over the course of the illness.

How long does the flu last?

A flu infection can last for up to two weeks, with an associated cough often lasting longer. Those affected often also feel weak for longer. It can take several weeks to fully recover from the flu.

How to treat the flu

With the flu, what the body needs most is rest. There are tried-and-tested home remedies that will help ease the symptoms. Here’s a selection:

Home remedies for the flu

• Herbal teas
  Anyone who has the flu should drink plenty of fluids. Best for the body are warm drinks, such as herbal and spiced teas with sage, thyme, chamomile, ginger or turmeric. They soothe the irritated and often painful mucous membranes and help to loosen the flu-induced mucus in the bronchial tubes and nose.

• Inhalation
  When inhaled, the warm steam cleanses the mucous membranes of the upper respiratory tract and stimulates blood circulation, which helps to loosen particularly stubborn mucus and improve breathing. All you need is a bowl of hot water and a towel to place over your head. You can also add salt to the water so the steam has a disinfectant effect on the respiratory tract. Medicinal herbs such as thyme or chamomile can also be added. Inhaling for 10 to 15 minutes is sufficient.

• Calf compresses
  Placing compresses around your calves can help reduce a temperature. Dip towels in cold water and wrap them around your calves. The cool compresses draw heat from the body and thus help to reduce the fever. Compresses should only be used if you’re not suffering from chills or are cold.

• Gargling
  You can also use the tea to gargle. This helps ease a sore throat. Gargle several time a day with freshly prepared tea made from sage, hibiscus, chamomile, hollyhock or marigold.

• Throat compress
  Cool or warm throat compresses can also help ease a sore throat. Quark is often used for cooling compresses, while boiled potatoes, for example, are used for a warming compress.

• Nutrition
  The right nutrition can help speed up the recovery process. Focus primarily on plant-based foods – unlike animal-based foods, these have little to no ingredients that can increase inflammation in the body. In addition, vegetables, fruit and pulses provide valuable vitamins, minerals, dietary fibre, sulfides and flavonoids. Here’s a selection of healthy helpers: fresh fruit or vegetables such as carrots, broccoli, apples, potatoes, berries, kale and black and green tea. If the flu also causes diarrhoea, foods containing pectin such as apples (preferably grated with the peel), bananas and carrots (cooked) can help.

When should you see a doctor when you have the flu?

The body can usually handle flu viruses pretty well. However, severe courses can occur in patients of all ages. If you have several of the following symptoms, you should contact your family doctor as soon as possible:

• Difficulty breathing, rapid breathing or shortness of breath
• Pain on breathing or chest or abdominal pain
• Sustained dizziness, confusion, the person affected is hard to wake
• Seizures
• Lack of urination over several hours
• Severe muscle pain
• Feeling of weakness or restlessness
• Recurring flu symptoms such as fever or severe coughing after an initial improvement
• Worsening of chronic illnesses 

With children, the following symptoms also apply:

• Temperature of 40 degrees or more (with children younger than twelve weeks: any raised temperature)
• Blue/grey lips or face
• Ribs retract with every breath
• Chest pain 

Anyone suffering from the flu who is also at risk of severe complications (see below) should contact their family doctor immediately. This includes existing illnesses such as diabetes or asthma.

Protection against the flu: vaccination

The FOPH recommends that particularly people who are at additional risk of developing severe flu should be vaccinated against the influenza virus.

The risk group includes people over the age of 65, pregnant women, premature babies and infants up to two years of age, and people with chronic illnesses such as cardiovascular and respiratory diseases (e.g. asthma), metabolic disorders affecting the function of the heart, lungs and kidneys (e.g. diabetes or severe obesity), neurological diseases (e.g. Parkinson’s disease), liver diseases, renal insufficiency, asplenia or functional disorders of the spleen, immunocompromising diseases (e.g. HIV infection, cancer) or autoimmune diseases (if these are treated with immunosuppressants).

In order to better protect these people, not only they themselves, but also everyone who is in regular contact with them should be vaccinated against the flu. These include close relatives, people who look after babies, and healthcare professionals.

Complications of the flu

Flu viruses can lead to complications in the respiratory tract or the lungs - in rare cases they also attack other organs. The most frequent complications of the flu are:

• Pneumonia (bacterial): Caused by bacteria that are quick to invade lungs that are damaged by the flu.
• Pneumonia (viral): Flu viruses can also cause inflammation.
• Worsening of existing chronic pulmonary diseases, such as asthma or chronic obstructive pulmonary disease (COPD)
• Inflammation of the brain or meninges
• Inflammation of the heart muscle, the tissue around the heart muscle or the heart valves
• Middle ear infection (otitis media): Particularly with children, the flu can cause a middle ear infection. But children can also experience the other complications.

Risk groups

Generally speaking, people of any age can catch the flu – and be affected by complications. However, the risk of complications or a severe course of the disease is higher for certain people. These include:

• Older people
• People with pre-existing conditions such as diabetes and chronic heart or lung disease
• People with an immunodeficiency
• Children under the age of five, especially infants under the age of two
• Pregnant women – until two weeks after the birth
• Smokers

Sources:
Federal Office of Public Health (FOPH)
Robert Koch Institute
Stiftung Gesundheitswissen