What is pneumonia?
Pneumonia is an inflammatory condition of the lungs that primarily affects the microscopic air sacs known as alveoli. It occurs when these air sacs fill with fluid or pus due to infection, which bacteria, viruses, or fungi can cause. This inflammation leads to impaired gas exchange and can cause respiratory symptoms.
There are several types of pneumonia:
- Bacterial pneumonia: The most common type and is primarily caused by bacteria such as Streptococcus pneumonia. Subtypes include lobar pneumonia and bronchopneumonia.
- Viral pneumonia: Caused by viruses such as influenza, respiratory syncytial virus (RSV), and coronaviruses (including SARS-CoV-2/COVID-19).
- Mycoplasma pneumonia: Caused by the bacterium Mycoplasma pneumoniae and is often referred to as "walking pneumonia" due to its milder symptoms.
- Atypical pneumonia: Caused by various atypical pathogens such as Chlamydophila pneumoniae and Legionella pneumophila.
- Fungal pneumonia: Typically occurs in individuals with weakened immune systems, can be caused by fungi such as Pneumocystis jirovecii, which is associated with AIDS, or other fungi like Histoplasma and Coccidioides.
- Aspiration pneumonia: Occurs when food, liquid, or vomit is inhaled into the lungs, leading to infection.
Additional types such as community-acquired pneumonia (CAP) and hospital-acquired pneumonia (HAP) are named after how they spread; CAP spreads outside a healthcare setting, while HAP develops while a person is hospitalized and is often caused by more resistant bacteria.
Pneumonia symptoms
Pneumonia presents a range of symptoms that can differ in severity based on the individual's health and the type of pneumonia. The most typical symptoms include:
- Cough: Often a response to increased production of respiratory secretions such as phlegm or mucus, which may be green, yellow, bloody, or purulent.
- Fever: Accompanied by sweating and shaking chills.
- Respiratory distress: May worsen with activity or as pleural effusion sets in.
- Chest pain: Sharp or stabbing pain that intensifies with coughing and deep breathing, or may be pleuritic chest pain.
- Fatigue: General tiredness and low energy.
- Loss of appetite: Reduced desire to eat.
- Nausea or vomiting: Especially common in children.
- Rapid breathing: Shallow and fast breathing.
- Rapid pulse: Increased heart rate.
- Bluish tint: A bluish color to lips or fingernails, indicating low oxygen levels.
- Confusion: Particularly in older adults, who may experience changes in mental awareness or delirium.
Other symptoms present in older adults, younger children, or those with comorbidities such as chronic lung disease or compromised immune systems:
- Older adults: Confusion or changes in mental awareness, lower-than-normal body temperature, milder presentation of other symptoms
- Infants and young children: Fussiness and restlessness, trouble feeding, noisy breathing or grunting, pale skin or limpness, and decreased urination.
Viral pneumonia symptoms also include muscle pain and weakness alongside other typical pneumonia symptoms.
Causes of pneumonia
Pneumonia can be classified into types based on how the infection was acquired: community-acquired, hospital-acquired, or ventilator-associated pneumonia. Influenza, Streptococcus pneumoniae, and respiratory syncytial virus can all lead to developing pneumonia, especially in vulnerable populations like the young or elderly.










