La pneumonia is an infection of the lungs most often caused by a virus or a bacterium.

The infection more specifically affects pulmonary alveoli, those tiny balloon-shaped sacs located at the ends of the bronchioles (see diagram below). It usually affects only one of the 5 lobes of the lung (3 lobes in the right lung and 2 in the left), hence the term lobaire pneumonie. When pneumonia also affects the bronchi, it is called bronchopneumonia.

Pneumonia actually refers to very diverse infections which may be minor or life threatening. So, if pneumonia appears as a complication of a serious illness or in an elderly person, it can be fatal. In very rare cases, pneumonia can also be fatal in a healthy person.

The disease usually manifests as a cough often accompanied byexpectorationsshortness of breath fever and chills. Pneumonia is most often caught like the flu or a cold, by inhaling contaminated particles. In some cases, it occurs after another respiratory infection, such as the flu or bronchitis, which “degenerates” and settles in the alveoli of the lungs. Some of the symptoms can last for several weeks. It is usually not very contagious.

What are the causes of pneumonia?

Almost all pneumonia are caused by germs, virus ou bacteria. When the microbe attacks the lungs, the body responds by triggering an inflammatory reaction. The alveoli fill with pus and inflammatory fluid, resulting in breathing difficulties.

The physician must distinguish between two modes of pneumonia contraction: contraction in a hospital setting (nosocomial pneumonia) and contraction outside the hospital (community-acquired or “community-acquired” pneumonia). The nosocomial pneumonia are usually more dangerous, because they occur in people weakened by another disease. In hospital, pneumonia is often transmitted by mechanical ventilation (intubation) devices in intensive care units.

The exact type of bacteria or virus that causes pneumonia in a given patient is only known in half of cases¹⁷, in part because laboratory techniques are not efficient enough. For your information, here are the ones that are most commonly found in people with pneumonia.

The bacteria responsible for pneumonia

Bacterial infections most often cause typical pneumonia. Most of the time, bacteria Haemophilus influenzae, Staphylococcus aureus ou Streptococcus pneumoniae (causing pneumonia pneumococcus), are responsible for it.

La atypical pneumonia

It manifests with symptoms that may be less pronounced than typical pneumonia. For example, some people with pneumonia do not have fever or chest pain. Pneumonia then sounds like a respiratory infection, such as bronchitis, sinusitis or the flu (influenza). Among the bacteria that cause atypical pneumonia are Mycoplasma pneumoniae (causing mycoplasma pneumonia), Chlamydia pneumoniae et Legionella pneumophila (responsible for Legionnaire’s disease).

Viruses in question

The most common viruses responsible for pneumonia are viruses influence et parainfluenza, respiratory syncytial virus, cold viruses (rhinovirus), herpes-like viruses or the SARS virus. The influenza virus, that is, the flu virus, sometimes reaches the airways of the lungs and thus causes viral pneumonia. Subsequently, the respiratory system weakened by the viral infection can open the door to a potentially more serious bacterial superinfection.

Other, rarer causes of pneumonia

• La aspiration pneumonia occurs when some of the liquid in the stomach is drawn into the lungs. Bacteria in this fluid then reach the bronchi and airways and cause infection. This phenomenon usually occurs after anesthesia or as a result of a neurological disorder affecting the swallowing reflex or in the event of inhalation of his vomiting, due to overuse of alcohol or drugs.
• Inhaling some toxic products (kerosene, varnishes, paint thinners, etc.) or mold (during construction work, mainly in people whose immune system is weakened by immunosuppressive treatment), or an allergy to products used in the workplace can cause inflammation of the lungs and bleeding. These conditions increase the risk of pneumonia and can cause pneumonitis, inflammation of the lungs, of non-infectious origin.
• Tuberculosis can present as pneumonia.
• Pneumonia caused by parasite or fungus are mostly found in people with weakened immune systems. Pulmonary aspergillosis is one example, as is pneumocystosis (caused by a parasite).

Diagram of pneumonia

Who is affected by pneumonia?

According to the World Health Organization, in 2015, pneumonia was responsible for 15% of deaths in children under 5 years old. It is therefore a dangerous disease in young children, which is why the WHO recommends vaccination to prevent pneumonia. 

According to the Quebec Lung Association, between 200 and 000 Canadians have pneumonia each year and the mortality rate can reach 30% in certain populations (elderly people – over 65 years old – hospitalized, etc.). The pneumonia acquired in hospital affect 0,5% to 1% of hospitalized patients, but up to 40% of people on mechanical ventilation in intensive care¹⁷.

Read our article on people at risk 

Diagnosis: how do you recognize pneumonia?

The doctor assesses the symptoms, inquire about the family history and examine the lungs. He may do an x-ray of the lungs and request an analysis of pulmonary secretions (expelled by coughing). If necessary, he will have to do other tests, such as looking for bacteria in the blood.

See the symptoms of pneumonia in detail 

What are the complications?

Pneumonia is usually healed in 2 weeks or a little longer. However, it often takes more time to fully recover.

Although they are rare, some serious complications are possible.

• Un pleural effusion. It is the accumulation of inflammatory fluid between the two layers of the pleura that causes compression of the lung. If there is a lot of liquid, it should be removed by suction. Exceptionally, this fluid may persist and become purulent. Surgery is then often necessary.
• Un abscess in the lung.
• A respiratory distress. When pneumonia affects both lungs, breathing becomes extremely difficult. Assisted ventilation is often necessary.
• Un septic shock, that is, a generalized infection of the body caused by the passage of the bacteria from the lungs to the blood. This occurs especially with pneumococcal pneumonia.

Thanks to antibiotics, pneumonia causes much less death than before. Still, pneumonia and influenza (influenza) are, both together, the leading cause of death from infectious disease in Canada.¹. very old people, whose immune system is weaker, and people with another serious illness are the most likely to succumb to it.

Read “pneumonia treatments”