Pneumonia is an infection of the lung. The lungs fill with fluid and make breathing difficult. Pneumonia disproportionately affects the young, the elderly, and the immunocompromised. It preys on weakness and vulnerability.

Bacteria, viruses and fungi can cause pneumonia. Treatment with antibiotics is usually needed. Patients with pneumonia may need to be hospitalized or even go to the intensive care unit (ICU). After developing pneumonia, it often takes 6-8 weeks until a patient returns to their normal level of functioning and wellbeing. While successful pneumonia treatment often leads to full recovery, it can have longer term consequences.Children who survive pneumonia have increased risk for chronic lung diseases. Adults who survive pneumonia may have worsened exercise ability, cardiovascular disease, cognitive decline, and quality of life for months or years.

The course of pneumonia can range from mild to life-threatening. The severity is mainly depends on:

The type of organism causing the infection

Viral pneumonia caused by the influenza virus may be severe and sometimes fatal. The virus invades the lungs and multiplies; however, there are almost no physical signs of lung tissue becoming filled with fluid. This pneumonia is most serious in people who have pre-existing heart or lung disease and pregnant women. After someone have had the flu, bacterial pneumonia can occur. This infection can quickly spread through the bloodstream and the entire body. People recovering from surgery, people with respiratory diseases or viral infections and people who have weakened immune systems are at greatest risk.

The development of complications

Even with treatment, some people with pneumonia may experience complications, including:

• Bacteria in the bloodstream (bacteremia): Bacteria that enter the bloodstream from your lungs can spread the infection to other organs, potentially causing organ failure.
• Difficulty breathing: If your pneumonia is severe or you have chronic underlying lung diseases, you may have trouble breathing in enough oxygen. You may need to be hospitalized and use a breathing machine (ventilator) while your lung heals.
• Fluid accumulation around the lungs (pleural effusion): Pneumonia may cause fluid to build up in the thin space between layers of tissue that line the lungs and chest cavity (pleura). If the fluid becomes infected, you may need to have it drained through a chest tube or removed with surgery.
• Lung abscess: An abscess occurs if pus forms in a cavity in the lung. An  abscess is usually treated with antibiotics. Sometimes, surgery or drainage with a long needle or tube placed into the abscess is needed to remove the pus.

Your age

Pneumonia is the world’s leading cause of death among children under 5 years of age. It is also the most common cause of hospital admissions. While young healthy adults have less risk of pneumonia than the age extremes, it is always a threat. Older people have higher risk of getting pneumonia, and are more likely to die from it if they do.

Your general health

If you were previously well, with treatment, you are likely to make a full recovery. Occasionally, some people who were previously well die from pneumonia. If you are already in poor health, you are more likely to become seriously ill with pneumonia. Pneumonia is a common cause of death in people who are already unwell – for example, people in the late or terminal stages of a cancer.