Pneumonia is inflammation of lung tissue. The lung is necessary for proper exchange of breathing gases and its damage may have acute and serious consequences. The pneumonias can be divided into several groups.
Before reading further, I would like to emphasize the meaning of the word “inflammation”. The word inflammation is not the same as the word “infection”. Inflammation is a common defensive response of the immune system. By inflammation, our body reacts not only to infections, but also to irritating non-infectious factors (burns, chemicals, etc).
The first possible division of pneumonias is therefore into infectious and non-infectious pneumonia.
These pneumonias can be caused by virtually any microorganisms such as bacteria, viruses and fungi. Repeated infectious pneumonias may occur in patients with immune disorders, congenital defects of the lungs, in bronchiectasis, cystic fibrosis and other conditions.
These pneumonias are caused by various liquid and gaseous chemicals that are inhaled. These substances can behave very aggressively and significantly injure the lung tissue. The situations include accidentally drunk (and inhaled) gasoline, inhalation of industrial chemical gases and aspiration of acidic gastric content (Mendelson's syndrome). Of course, non-infectious pneumonia usually weakens the mucosa and increases risk of subsequent infectious pneumonias.
Further text shall be dedicated to infectious pneumonias as they are much more common and clinically significant.
Bacterial infectious pneumonia
Common type of bacterial pneumonia is caused by bacteria such as streptococci (pneumococcus), haemophilus and others. Bacteria usually enter the lungs from the upper airways. People with cystic fibrosis and hospitalized patients have increased risk of infection by Pseudomonas bacterium.
Bacterial pneumonia tends to have more significant symptoms including high fever, malaise, cough and shortness of breath. The cough is usually productive with expectoration of mucus or pus. Larger pneumonia may even cause coughing up blood.
The primary method of treatment is antibiotic therapy. The type, dosage and method of administration is individual. Young and otherwise healthy people with mild symptoms may be treated in outpatient regime, other cases should be hospitalized.
Note: Specific bacteria (such as Legionella) or intracellular parasites (chlamydia, mycoplasma) may cause pneumonia, which resembles by its course and symptoms the viral pneumonia (see below). These pneumonias are treated with slightly different antibiotics that are effective against the mentioned microorganism. Totally specific issue is the lung inflammation caused by bacterial tuberculosis.
Viral infectious pneumonia
This type of pneumonia may be caused by many viruses such as influenza virus, cytomegalovirus and sometimes even by herpesvirus.
The symptoms are usually less dramatic than in bacterial pneumonias. The affected person suffers from unpleasant irritating dry cough, dyspnea, chest pain and milder elevation of temperature (usually below 38°C). However, the symptoms may be also stronger and the infection can be even fatal. N addition, viral pneumonia may be followed by bacterial infection.
We do not have such efficient therapy as against bacterial infections. The treatment is therefore mainly symptomatic. Special antivirotics can be used only against certain viruses.
Fungal infectious pneumonia
These pneumonias are caused by fungi. They do not occur in otherwise healthy people, but they can be anticipated in people with significantly weakened immunity, for example people taking immunosuppressive drug and patients with AIDS. Pneumocystis carinii is a microorganism typical for severe pneumonias in such patients.
Special antifungal drugs are used together with classic supportive therapy. Pneumocystis carinii is sensitive to a chemical substance known as cotrimoxazole.
In a patient with typical clinical signs, we should perform cautious physical examination including listening the lungs with a stethoscope. When listening, we can hear characteristic sounds. Blood test may be used to confirm signs of infection such as elevated CRP and sedimentation rate. Imaging methods are very important to show the infiltrated lung tissue – chest X-ray is the basic examination and in case of need it may be followed by computed tomography. We should also do microbiological examination (tracheal swab, microbiological examination of sputum, blood cultures) to try to find the causing microorganism. In case that the microorganism is a bacterium, it is necessary to know its sensitivity to antibiotics.
As the pneumonia usually occurs after an infection of respiratory tract, it is advisable to carefully treat any of these infections including bed rest and plenty of fluids and, when needed, antibiotics. Preventive vaccination against influenza and pneumococcal infections is advisable in the elderly and immunocompromised patients.