Pneumonia

Pneumonia is an infection of the lungs that causes inflammation in the small air sacs (alveoli) responsible for exchanging oxygen and carbon dioxide with the bloodstream. When these air sacs become infected, they can fill with fluid or pus, reducing the lungs' capacity to take in oxygen and causing the characteristic cough, fever and breathing difficulty associated with the condition. Pneumonia can affect one or both lungs, and can range from mild to severe, occasionally becoming life-threatening, particularly in young children, older adults, and those with weakened immune systems or underlying health conditions.

Pneumonia is most often caused by bacteria, viruses, or, less commonly, fungi, and frequently develops following an upper respiratory tract infection such as a cold or the flu. It can spread through airborne respiratory droplets released when an infected person coughs or sneezes, through contact with contaminated surfaces, or, in healthcare settings, via a ventilator. Pneumonia can also result from inhaling (aspirating) food, saliva, or stomach contents into the lungs.

Pneumonia may affect a small area of one lung or involve larger areas of both lungs. It may develop suddenly over a few days or occur after another respiratory infection. In some cases, particularly in older adults, symptoms may be less typical and may include weakness, confusion or a decline in usual daily functioning.

Types of Pneumonia

Pneumonia is generally classified according to where and how it was acquired, which has an important bearing on the likely causative organism and the most appropriate treatment approach.

• Community-Acquired Pneumonia: The most common type, occurring outside of hospitals or other healthcare facilities. May be caused by bacteria such as Streptococcus pneumoniae, viruses, or, less commonly, fungi.
• Hospital-Acquired Pneumonia: Develops during a hospital stay for another illness, typically starting 48 hours or more after admission. Tends to be more serious, as the causative bacteria may be more resistant to standard antibiotics. Patients on ventilators in intensive care units are at particularly high risk.
• Healthcare-Associated Pneumonia: Occurs in people who live in long-term care facilities, or who receive regular outpatient care such as dialysis. Similar to hospital-acquired pneumonia, it may be caused by more antibiotic-resistant bacteria.
• Aspiration Pneumonia: Develops when food, liquid, saliva, or stomach contents are inhaled into the lungs instead of being swallowed normally, introducing bacteria directly into the lower airway. More common in people with swallowing difficulties, reduced consciousness, or certain neurological conditions.

How Pneumonia Develops

Understanding what happens inside the lungs helps explain why pneumonia produces the symptoms it does:

• Entry of the infecting organism: Bacteria, viruses or fungi enter the lower respiratory tract, either after being inhaled, spreading down from an existing upper respiratory infection, or through aspiration.
• Infection of the alveoli: The infecting organism multiplies within the small air sacs (alveoli) of the lungs, triggering the immune system's inflammatory response.
• Fluid and pus accumulation: Inflammation causes the alveoli to fill with fluid and pus, which is what typically shows up as areas of consolidation on a chest X-ray or CT scan.
• Reduced oxygen exchange: Fluid-filled alveoli are far less efficient at transferring oxygen into the bloodstream and removing carbon dioxide, leading to lower blood oxygen levels and the sensation of breathlessness.
• Systemic response: The body's broader immune response to the infection produces fever, chills, and fatigue, as the body works to fight off the infecting organism.

Symptoms of Pneumonia

Symptoms of pneumonia can vary depending on the cause of the infection, your age, and your overall health. Mild cases may resemble a common cold or flu, but tend to last longer and can include:

• Cough, often producing phlegm or mucus
• Fever, sweating and shaking chills
• Chest pain that worsens when breathing deeply or coughing
• Shortness of breath
• Fatigue
• Nausea, vomiting or diarrhoea
• Confusion, particularly in older adults
• Lower than normal body temperature, particularly in older adults or those with weakened immune systems

Symptoms can present somewhat differently depending on age.

Infants and young children may show few specific symptoms and instead appear generally unwell, feed poorly, or become unusually irritable or lethargic. Older adults may develop confusion or a noticeable decline in alertness as one of the most prominent signs, sometimes with only a mild cough or low-grade fever, or none at all — which is why pneumonia can be easy to miss in this age group.

What Causes Pneumonia

neumonia can be caused by several different types of infecting organism, each with somewhat different characteristics:

• Bacteria: The most common cause of pneumonia requiring hospitalisation, with Streptococcus pneumoniae being one of the most frequently identified organisms. Bacterial pneumonia can occur on its own or develop as a complication following a viral respiratory infection.
• Viruses: Including influenza, respiratory syncytial virus (RSV), and coronaviruses, among others. Viral pneumonia is generally milder than bacterial pneumonia, though it can still be serious, particularly in vulnerable individuals.
• Fungi: A less common cause, more likely to affect people with chronic health conditions or weakened immune systems, or those who have inhaled large amounts of certain fungal spores from the environment.
• Aspiration: Inhaling food, liquid, saliva, or vomit into the lungs can introduce bacteria directly into the lower airway, leading to aspiration pneumonia.

Pneumonia-causing organisms can spread through airborne droplets released by coughing or sneezing, through contact with contaminated surfaces or objects, or, in hospital settings, via contaminated equipment such as ventilators.

Risk Factors for Pneumonia

Pneumonia can affect anyone, but certain groups and factors carry a significantly higher risk:

• Age: Children under 2 years and adults aged 65 and above are at the highest risk of developing pneumonia and of experiencing more severe illness.
• Hospitalisation, particularly in intensive care: Being hospitalised, especially in an intensive care unit or on a ventilator, significantly increases the risk of hospital-acquired pneumonia.
• Chronic disease: Conditions such as asthma, chronic obstructive pulmonary disease (COPD), heart disease, and diabetes increase susceptibility to pneumonia and the risk of more severe illness.
• Smoking: Damages the lungs' natural defences against infection, increasing both the risk of developing pneumonia and the severity of illness.
• Weakened or suppressed immune system: People with HIV/AIDS, those who have had an organ transplant, are undergoing chemotherapy, or have used long-term steroid medication are at increased risk.
• Swallowing difficulties or reduced consciousness: Conditions that increase the risk of aspiration, such as stroke or certain neurological disorders, raise the risk of aspiration pneumonia.
• Living in group settings: Nursing homes, long-term care facilities, and other group living environments can facilitate the spread of pneumonia-causing organisms.
• Malnutrition: Poor nutritional status can weaken the immune system's ability to fight off respiratory infections.

Possible Complications of Pneumonia

Most people recover fully from pneumonia with appropriate treatment, but in more severe cases, or in vulnerable individuals, complications can develop:

• Bacteraemia and sepsis: Bacteria from an infected lung can spread into the bloodstream, potentially triggering a severe, body-wide inflammatory response (sepsis) that requires urgent treatment.
• Pleural effusion: Fluid can accumulate in the space between the lung and chest wall (the pleural space), which may need to be drained if it becomes infected (empyema) or causes significant breathing difficulty.
• Lung abscess: A pocket of pus can form within the lung tissue, usually requiring prolonged antibiotic treatment and occasionally drainage.
• Acute respiratory distress syndrome (ARDS): A severe, life-threatening form of lung failure that can develop in the most serious cases of pneumonia, requiring intensive care support.
• Respiratory failure: Severe pneumonia can impair the lungs' ability to maintain adequate oxygen levels, sometimes requiring supplemental oxygen or mechanical ventilation.
• Worsening of underlying conditions: Pneumonia can significantly worsen existing heart or lung disease, and in older or frail patients, may trigger a broader decline in overall health and function.

How Pneumonia is Diagnosed

If pneumonia is suspected based on your symptoms and a physical examination, several tests are used to confirm the diagnosis, identify the causative organism, and assess severity.

• Physical Examination: Your doctor will listen to your lungs with a stethoscope for abnormal sounds such as crackling or bubbling, which can suggest fluid or infection in the lungs.
• Blood Test: Checks for elevated white blood cell levels, which can indicate an infection, and helps assess overall severity of illness.
• Imaging Tests (X-ray, CT or Ultrasound): Lung imaging is used to identify areas of infection or fluid build-up in the lungs, confirm the diagnosis, and assess the extent of the pneumonia.
• Pulse Oximetry Test: A simple, non-invasive test that measures the level of oxygen in your blood, helping to assess how significantly the infection is affecting your breathing.
• Sputum Test: A sample of coughed-up mucus is examined to help identify whether the infection is caused by bacteria, a virus, or a fungus, guiding the choice of treatment.

Recovering From Pneumonia

Recovery time from pneumonia varies considerably depending on the severity of the infection, the causative organism, and your overall health, but most people begin to feel better within a week or two of starting treatment, although a full recovery can take several weeks longer.

Fatigue and a lingering cough are common for some time after the acute infection has cleared, and it's normal for it to take a while before you feel fully back to your usual energy levels. Gradually resuming normal activity as your strength returns, rather than pushing straight back into a full routine, generally supports a smoother recovery. It is important to complete the full course of any prescribed antibiotics, even once you start to feel better, as stopping early can allow the infection to return or contribute to antibiotic resistance.

A follow-up appointment, sometimes including a repeat chest X-ray several weeks after treatment, may be recommended — particularly for older adults, smokers, or those with more severe pneumonia — to confirm the infection has fully resolved.

How to Prevent Pneumonia

• Get vaccinated: Vaccines are available to help prevent certain types of bacterial pneumonia, as well as influenza, which can lead to pneumonia as a complication.
• Practise good hygiene: Wash your hands regularly, or use an alcohol-based hand sanitiser, to reduce the spread of respiratory infections that can lead to pneumonia.
• Quit smoking: Smoking damages the lungs' natural defences against respiratory infection; quitting meaningfully reduces your risk.
• Manage chronic health conditions: Good control of conditions such as asthma, COPD, diabetes and heart disease helps reduce your overall susceptibility to pneumonia.
• Avoid close contact with people who are unwell: Limiting exposure to those with respiratory infections, particularly if you are in a higher-risk group, can help reduce your chance of infection.
• Maintain a healthy lifestyle: A balanced diet, regular exercise and adequate sleep support a well-functioning immune system.