What are pneumonia and its risk factors?

Pneumonia is the infection that causes the most significant number of hospital admissions. Although its usual cause is bacteria, viruses such as influenza and chickenpox can also cause this disease.

Pneumonia is an inflammation of lung tissue caused by an infectious agent. It can affect one or both lungs. The lung is made up of two main parts: the bronchi (tubes through which the air passes) and the alveoli (small air sacs, in which the exchange of oxygen that passes into the blood and carbon dioxide expelled takes place To the exterior). In pneumonia, the alveolus is affected; it becomes irritated and inflamed and fills with fluid and infectious material or pus, making it painful for the person to breathe.

Depending on the patient’s previous condition and age and depending on the cause of the infection (bacteria, viruses, or, to a lesser extent, fungi), pneumonia can be mild or severe. Along with difficulty breathing normally, other symptoms may appear, ranging from fever or cough with phlegm to chest pain, chills, nausea, or diarrhea. Children can be restless or tired, while older adults can have mental state changes and even temperature drops.

It is the infection that causes the highest number of hospital admissions, and in 2019 2.5 million people died from it worldwide (including 672,000 children), a number that is expected to increase due to the aging of the population and the increase in patients with chronic diseases that make them more vulnerable to complications. 

It most frequently affects young people and the elderly (23-34 cases per 1,000, in those over 75 years of age ), mainly institutionalized elderly (living in nursing homes or centers for the elderly). It predominates in males and the winter season. It is also one of the diseases that causes the most infant deaths, especially in the case of neonatal pneumonia (in newborns): health authorities estimate that nearly 1,200,000 children under the age of five die each year as a result of pneumonia.

In most cases (70-80%), pneumonia treatment is carried out outside the hospital. Pneumonia can cause certain serious complications, ranging from bacteremia leading to septic shock to respiratory or kidney failure, or pleural conditions, or lung abscesses.

Risk factors for pneumonia

Here are the most common risk factors that can lead to pneumonia:


: Chronic diseases or pathologies previous lung diabetes mellitus, liver disease, heart disease, kidney disease, cancer, chronic lung disease, AIDS.

Coronavirus disease (COVID-19 ).




Age (children under two years of age and people over 50, especially those over 65, are the most susceptible to pneumonia).

Splenectomy (patients whose spleen has been removed) and, in general, patients with a low level of immunity.


Immunosuppressive or chronic corticosteroid treatments that weaken the immune system.

Residents in centers for the chronically ill or elderly.

Being admitted to a hospital, especially an ICU, sedated or requiring mechanical ventilation.

Exposure to parenteral drugs.

Exposure to toxic fumes, pollutants, or certain chemicals.

Causes of pneumonia

The mechanism by which most pneumonia occurs is the aspiration of microorganisms from the oropharynx. However, the responsible agent may not be determined in up to 50% of cases. The most likely etiology will depend on the acquisition, associated risk factors, geographic location, and infection severity.

Causes of pneumonia in adults and the elderly

The most common causes of pneumonia in adults are bacteria, such as Streptococcus pneumonia (pneumococcus), Staphylococcus aureus, Legionella pneumophila, Mycoplasma pneumonia, Chlamydia pneumonia, and Haemophilus influenzae. However, up to 10% can be caused by several of these agents simultaneously. 

Viruses such as influenza, SARS-CoV-2 coronavirus, respiratory syncytial virus, and chickenpox can also cause pneumonia.

Also, some fungi can cause pneumonia (fungal pneumonia), for example, in patients with weakened immune systems, for example, those with HIV-AIDS, or chronically ill patients: Pneumocystis pneumonia, Coccidioidomycosis (causing what is known as valley fever), Histoplasmosis or Cryptococcus.


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