Inflammation of the lungs (pneumonia)

Pneumonia is usually caused by an infection. You can find out everything about symptoms, diagnosis and therapy here

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Pneumonia - briefly explained

Inflammation of the lungs (pneumonia) usually occurs due to an infection with bacteria, viruses or fungi. Depending on the type of inflammation, it takes place in the area of ​​the alveoli and / or in the tissue between the lungs. The tissues involved are thickened, so that the path for oxygen from the alveoli to the bloodstream is lengthened. This reduces the oxygen saturation of the blood. In addition to general symptoms such as exhaustion, reduced performance, headaches and aches and pains, pneumonia usually leads to fever and cough. Depending on the severity, there is also shortness of breath. Pneumonia therapy depends on the type of trigger. Antibiotics help with bacterial infections. In all forms of pneumonia, measures such as bed rest, breathing exercises and inhalations are used. If the oxygen supply is insufficient, it may be necessary to supply oxygen up to and including mechanical ventilation in the intensive care unit. If the therapy works and there are no further complications, the pneumonia usually heals within two to three weeks. Inflammation of the pleura, accumulations of pus in the lungs (abscesses) or other complications can make recovery much more difficult. Even today there are cases in which patients die. Pneumonia is still the most common fatal infectious disease in Germany.

What is pneumonia?

In pneumonia, the alveoli and / or the lung tissue between them are inflamed. The inflammation leads to a thickening of the tissue, which makes gas exchange between the lungs and blood vessels increasingly difficult (see also Background Information: Gas Exchange).

The cavities, which are important for gas exchange, are compressed in bacterial pneumonia by purulent material and water retention in the tissue and are no longer available for the exchange of breathing gases. Even with so-called atypical pneumonia caused by viruses or fungi, the inflammation mainly takes place in the tissue between the lungs, the interstitium. Here, too, there is a thickening of the lung tissue, which makes gas exchange more difficult. Both for diagnosis and therapy, however, it is not decisive where exactly the inflammation takes place, but rather what caused it.

According to estimates, 500,000 people fall ill each year in Germany alone at home or in their usual environment (community-acquired pneumonia), almost a third of them require hospital treatment. This means that more people are admitted to the clinic with pneumonia than with a heart attack or stroke. In addition, there are cases where patients are hospitalized for other reasons and develop pneumonia there (nosocomially acquired pneumonia).

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Background information - gas exchange in the lungs

The alveoli are covered with blood vessels (capillaries). This is where the gas exchange between the blood and the air takes place. On the one hand, vital oxygen reaches these points from the air we breathe into the blood vessels of the lungs and with the bloodstream to the organs and tissues. On the other hand, the blood in the pulmonary vessels releases the metabolic product carbon dioxide back into the alveoli so that it can be exhaled.

What happens now with pneumonia?

If the alveoli or the tissue between the lungs (interstitium) become inflamed, these structures become thickened. This increases the distance that the oxygen molecules have to travel to migrate (diffusion) from the alveoli into the blood vessels and the red blood pigment (hemoglobin) is less saturated with oxygen molecules. Carbon dioxide, on the other hand, is still well released from the bloodstream, since its diffusion speed ("migration speed") is significantly faster.


The cause of pneumonia is usually an infection of the alveoli and / or the lung tissue with bacteria, more rarely with viruses, fungi or parasites. However, some pneumonia are also caused by other stimuli, such as inhaled gases, dust or radiation. A pronounced circulatory disorder in certain sections of the lung and a bronchus blocked by a foreign body or tumor can also promote inflammation of the affected lung section. There is also aspiration pneumonia, in which food pulp, stomach acid or stomach contents get into the trachea and ultimately also into the lungs. They either damage lung tissue directly or provide the basis for infection.

Infectious pneumonia
Wherever people live closely together, pathogens are always in circulation. For example, if a patient has a respiratory tract infection, a sneeze or cough is enough to release countless germs bound to droplets. They are then inhaled by others and can colonize their airways. This type of infection route is called droplet infection.

Pneumonia is usually the result of such an infection through droplet infection. In principle, they can be triggered by many different types of bacteria, but also by viruses, fungi (e.g. Aspergillus species or Candida) or parasites. However, the pathogens can also come from your own mouth if, for example, saliva gets into the windpipe.

If people get infected in their everyday environment, doctors speak of community-acquired pneumonia. This is important because the pathogens are different from those of hospital-acquired pneumonia. Community-acquired pneumonia is mainly triggered by bacteria, especially pneumococci. But flu and other viruses can also cause pneumonia and / or promote a bacterial infection.

Diseases that are infected in hospitals are called nosocomial. They occur preferentially under intensive medical treatment. There are various reasons for this: On the one hand, the patients who are in an intensive care unit are usually seriously ill, so that their immune system can no longer defend itself so well against germs. On the other hand, certain therapeutic measures - such as long-term mechanical ventilation and intubation (i.e. a tube in the windpipe) - can increase the risk of developing pneumonia.The reason for this is that patients on mechanical ventilation and with a tracheal tube (tube) receive drugs that cause an artificial coma or twilight sleep. This also affects the cough reflex, which would be necessary to clean the trachea and bronchi. It is not uncommon for the pathogens of nosocomial pneumonia to be problematic germs that are difficult to treat, such as staphylococci or enterococci that are resistant to antibiotics.

Non-infectious pneumonia
Pneumonia is not always caused by an infection. Other possible causes are allergic reactions and physical or chemical stimuli such as gases, metal vapors and dust that get into the lungs. Ionizing radiation (for example, radiation therapy for cancer) can also cause pneumonia.

Circulatory disorders such as a pulmonary embolism or a congestion of blood in the lungs caused by a weakness of the left ventricle (left heart failure) can also promote pneumonia. Even if the bronchus is blocked by a foreign body or tumor, inflammation can occur in the inadequately ventilated section of the lung.

Aspiration pneumonia
Aspiration pneumonia occupy a special position. They occur when food, stomach acid or other stomach contents enter the lungs via the windpipe.

Particularly at risk are unconscious people and patients with swallowing disorders. Swallowing disorders often occur after a stroke, Parkinson's disease, multiple sclerosis, a traumatic brain injury or a brain tumor. In those affected, the motor skills of the mouth and throat are limited, often also the sensitivity in the area of ​​the vocal folds and the swallowing reflex.

Food residues enter the trachea instead of the esophagus and are finally inhaled (aspirated). In the event of vomiting or strong backflow of gastric juice into the esophagus, this can also penetrate the trachea if the appropriate protective reflexes are lacking. The aspirated material either damages the lung tissue directly - for example by burning it with stomach acid - or promotes infection.

Current topic: SARS-CoV-2

This is a short summary - you can find detailed information on our overview page for SARS-CoV-2.

  • What is the difference between SARS-CoV-2 and COVID-19?

SARS-CoV-2 is the name for the new coronavirus. It comes from the coronavirus family, but is a new strain in that group. The disease caused by the SARS-CoV-2 virus is then called COVID-19 (Coronavirus disease 2019). Therefore, for example, one spies on "SARS-CoV-2 carriers" or "people with COVID-19".

  • What is the course of a COVID-19 illness?

The course of the disease is very individual and different. Due to the high number of unreported cases of infected people, no reliable figures can yet be given regarding the infection. According to previous studies, many sufferers seem to show only mild symptoms or even no symptoms at all (81 percent). Around 14 percent have a severe course, around five percent develop a critical clinical picture.

  • How does pneumonia develop?

The pneumonia caused by SARS-CoV-2 is viral (atypical) pneumonia. This inflammation mainly takes place in the alveoli. The massive damage then leads to the sometimes life-threatening restriction of oxygen uptake.

  • What does a severe course mean, what are life-threatening complications?

If the course is severe, ARDS can develop (see complications). This is not specific to SARS-CoV-2 infections, but can apply to any other Develop pneumonia. A bacterial co-infection (an additional bacterial infection of the lungs) can also lead to a severe course. This can lead to blood poisoning (sepsis) with septic shock. Further complications can be cardiac arrhythmias, damage to the pericardium (myocardium) or acute kidney failure.

Risk factors

Not every contact with a germ immediately leads to pneumonia. The disease only breaks out when the body's defenses cannot keep the pathogens in check and eliminate them. This is especially possible in infants and people of old age, in whom the immune system is not yet fully developed, or whose defenses are gradually weakening again. On the other hand, it also depends on the direct amount of pathogen that has reached the lungs.

People at risk also include people with certain underlying diseases (e.g. diabetes, certain infectious diseases, alcoholism) as well as those whose immune system is restricted by therapy. This is the case, for example, when people have to take cortisone, chemotherapy drugs, or drugs that suppress the body's immune system (immunosuppressants). Pneumonia can also develop more easily if the lungs have previously been damaged by a disease (e.g. chronic bronchitis).


Typical symptoms, especially in bacterial pneumonia, are fever, chills and difficulty breathing, which can sometimes be absent or only mild. One speaks therefore of typical and atypical pneumonia.

Typical pneumonia, usually caused by bacteria, often begins quickly with pronounced symptoms such as chills and a rapid rise in body temperature. The fever can climb to 40 degrees. Further typical symptoms are cough with initially uncharacteristic, later rust-brown expectoration. Patients often feel weak and tired. Older people in particular are often confused or drowsy. Breath-dependent chest pain can also occur, which is a sign of inflammation of the pleura (pleurisy). Depending on the severity of the disease, breathing is impaired to a greater or lesser extent. The body tries to compensate for the reduced oxygen uptake by increasing the breathing rate; the pulse rate is also increased. If these measures by the body are not sufficient to remedy the lack of oxygen, the lips and the nail bed can discolour bluish (cyanosis).

Without antibiotics, the fever drops by the end of the first week of illness if there are no complications. Doctors speak of the crisis. The cardiovascular system is heavily stressed and the pulse rate slows down significantly. After a further one to two weeks, the patient will then ideally have survived the disease, although the general feeling of weakness and slight shortness of breath can last longer.

But this favorable course did not always occur: In the time before antibiotics were available, many - including young people - died of pneumonia. Today, the course described above, which is particularly typical for bacterial pneumonia caused by pneumococci, is rarely seen because the pneumonia is usually recognized and treated in good time.

In so-called atypical pneumonia, the symptoms deviate from the typical picture mentioned above. This form of pneumonia usually begins more slowly, and the rise in body temperature (fever) is often less. General symptoms such as headache and body aches and significant fatigue can also occur here. Usually only a so-called dry, tickly cough with little or no sputum appears.


Typical pneumonia: the pneumonia is caused by a bacterial infection (mostly by Streptococcus pneumoniae). This type of pneumonia often takes place in the alveoli in certain lobes of the lungs (lobar pneumonia). The symptoms are usually characterized by a sudden onset with chills and a high fever. A so-called productive cough is also often found, i.e. the cough is associated with sputum.

Atypical pneumonia: Atypical pneumonia is a pneumonia that is triggered by a different spectrum of pathogens, such as viruses or smaller bacteria. It often takes place in the spaces between the lungs (interstitium). The symptoms are often more unspecific (atypical) with a slow onset of symptoms, a lower increase in fever and a dry cough (without sputum).


Pneumonia can also be very complicated, for example if the treatment does not start in time and the pneumonia is delayed, if the therapy is not sufficiently effective or if there are concomitant diseases. Complications that affect the lungs themselves are, for example, inflammation of the lungs (pleurisy), accumulation of fluid between the lungs and pleura (pleural effusion) or the formation of pus-filled cavities (lung abscess). In addition, some bacterial pathogens can spread to other parts of the body and organs and cause blood poisoning (sepsis) or affect the meninges, the middle ear or the heart.

A notable complication of pneumonia is the development of ARDS - see extra box.

If signs of pneumonia are still present on the x-ray after six to eight weeks, the disease has become chronic. This course is mainly observed in patients with weakened immune systems and chronic diseases.


  • Acute lung failure (ARDS, Acute Respiratory Distress Syndrome)

Actual lung failure is a rapidly increasing (acute) breathing problem in people with healthy lungs. The most common causes of ARDS are pneumonia, but other lung-damaging causes such as inhaling smoke gases, swallowing stomach contents (aspiration), shock or blood poisoning (sepsis) can lead to ARDS. The inflammatory reaction of the lung tissue leads, on the one hand, to an increasing accumulation of water in the lungs (pulmonary edema), so that the possibility of gas exchange in the lungs increasingly deteriorates and the oxygen supply to the body can no longer be guaranteed. On the other hand, the inflammation causes a connective tissue remodeling of the lung tissue (pulmonary fibrosis), which also affects the gas exchange and the elasticity of the lungs.


Symptoms of pneumonia are sometimes difficult to differentiate from those of a cold or other respiratory infections. Since pneumonia must be treated as early as possible, you should consult a doctor quickly if you suspect it.

Physical examination and medical history:

He will first have the patient's medical history detailed (anamnesis) and listen to the chest. In some cases pneumonia is accompanied by altered breathing sounds. He may also knock the lungs and measure the body temperature.

Imaging procedures:

If pneumonia is suspected or the origin of the symptoms remains unclear, the doctor will have a chest x-ray made. In the case of pneumonia, it can be used to identify inflammatory compression of the tissue and show the extent and location of the affected lung sections.

Laboratory chemical investigations:

A blood sample can often be used to determine whether there is an inflammation. There are certain levels in the blood that increase when there is inflammation. These include the number of white blood cells, the sedimentation rate and the C-reactive protein.

Indications of the pathogen can also be found in the blood: On the one hand, the detection of defense substances (antibodies) directed against the germ and a blood culture in which the bacteria contained in the blood are grown are suitable. The pathogen may also be found in the sputum (sputum analysis). However, an analysis of the sputum is not made in principle. However, it can be useful for patients in hospital, with complicated courses or if the doctor suspects an infection with rare pathogens.

Further measures:

Further diagnostic measures usually only follow in the case of unclear findings, non-infectious pneumonia, severe courses or complications. This includes the ultrasound examination (sonography), with which, for example, a pleural effusion can be determined. Computed tomography can help assess the location and extent of the inflammation more precisely. A pulmonary perfusion scintigraphy, in which the blood flow to the lungs is examined with the help of radioactive substances, is an option if a pulmonary embolism or other circulatory disorder is suspected. Examination of the bronchial tree (bronchoscopy) reveals foreign bodies or tumors in the airways. The doctor can also combine it with irrigation of the bronchi (bronchial lavage). In doing so, he wins fluid that contains the pathogen, which can be examined in the laboratory to determine the causative germ.


The chapter "Therapy" mainly refers to infectious pneumonia. An important question in their treatment is whether the patient can stay at home or must be admitted to hospital. As a rule, the decision is based on certain accompanying circumstances and the severity of the illness. Criteria that speak for a briefing are, for example:

  • an age over 65 years
  • an insecure domestic supply situation
  • an alcohol addiction
  • widespread pneumonia
  • the presence of comorbidities
  • Disorders of consciousness, breathing or circulation

Therapy of infectious pneumonia

  • Antibiotics

In the case of bacterial pneumonia, the administration of antibiotics is an essential part of the treatment. Therapy usually begins without precise knowledge of the pathogen. Rather, the doctor assumes a certain spectrum of germs based on the circumstances of the disease and selects a suitable antibiotic. He can orientate himself on guidelines and therapy recommendations published by the medical professional associations. In addition, there are other aspects that must be taken into account when choosing a therapy. These include, for example, individual intolerances, chronic illnesses and pregnancy or breastfeeding.

Individual strains can be insensitive to one or the other antibiotic or become so over time. This is known as antibiotic resistance. Antibiotic resistance is a problem especially in hospitals. The frequent use of antibiotics in these facilities can result in the formation of strains that are insensitive to one or more antibiotics. The treatment then turns out to be correspondingly difficult.

Doctors and patients can also contribute to the selection of resistant strains through their behavior. For example, the prescription of antibiotics for virus-related pneumonia is only justified if an additional bacterial infection is present or at least to be assumed. Otherwise the gift is useless because viruses do not respond to antibiotics. Patients, on the other hand, should always make sure to take the prescribed antibiotics for as long as the doctor intended. This also applies if the condition has already improved.

If there is no improvement within two to three days, the doctor will either change the drug dose, prescribe a different drug, or question his diagnosis. The results of the blood test are usually also available at this point in time. If the pathogen can be identified, the doctor knows whether the antibiotic administered is effective against it. If not, he will adjust the treatment accordingly.

  • Other measures

In the case of pneumonia caused by fungi or parasites, drugs that are especially effective against these pathogens may be given. Further measures are mainly limited to alleviating the symptoms and preventing secondary diseases. This includes rest, in the case of a fever also bed rest, which may then require measures (blood thinning, thrombosis stockings) to prevent the formation of blood clots (thrombi).

Patients should support recovery by taking it easy and giving the body time to regenerate. So don't stop taking your medication too early and start working again! Otherwise there is a risk of relapses, which are often worse than the initial illness.

If necessary, the mucus can be loosened with saline inhalations or by therapy with expectorants, so that coughing up is easier. Adequate fluid intake is particularly important if the doctor has prescribed expectorants or if there is a high fever. Otherwise healthy people can usually rely on their feeling of thirst. However, this is not always reliable for young children and the elderly. Here you should therefore pay particular attention to a suitable amount of drink, which must be clarified with the doctor beforehand. Because especially in people with heart or kidney disease, excessive fluid intake can be harmful.

If the mucus cannot be coughed up, it can help if the doctor or nursing staff suction the bronchi.Breathing exercises or tapping massages can also make breathing easier. Finally, the doctor will also ensure that any comorbidities are treated.

If the oxygen supply is inadequate, it may make sense to supply the gas through a nasal cannula. In extreme cases, the patient must be ventilated - either with so-called NIV ventilation (non-invasive ventilation, mask ventilation) or with a ventilator and a tracheal tube (tube) in the intensive care unit (invasive ventilation).

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