Last Updated on October 18, 2025 by Analgesia team
Community-acquired pneumonia in Adults
CAP is the medical abbreviation for community-acquired pneumonia, a lung infection that develops outside of a hospital. It can be caused by several bacteria, viruses, fungi, and parasites. Symptoms can range from mild to severe, and can be very serious in older adults, young children, and people with other health problems.
The most common cause of community-acquired pneumonia is Streptococcus pneumoniae, a type of bacteria.
Here are some other things to know about Community-acquired pneumonia:
Community-acquired pneumonia in children
Community-acquired pneumonia (CAP) in children occurs when an infection develops in the lungs outside a hospital setting. It’s most commonly caused by bacteria such as Streptococcus pneumoniae or viruses like the flu and respiratory syncytial virus (RSV). Symptoms often include fever, cough, chest pain, rapid breathing, and fatigue.
Children with CAP may also show signs such as poor feeding, irritability, or vomiting. The severity depends on the child’s age, overall health, and the type of organism causing the infection. Diagnosis usually involves a physical exam, chest X-ray, and sometimes blood or sputum tests to identify the pathogen.
Treatment typically includes antibiotics for bacterial cases and supportive care such as fluids, rest, and fever control for viral infections. In severe cases, hospital admission may be required to manage breathing difficulties and dehydration. Early treatment is key to preventing complications such as pleural effusion or lung abscess.
Community-acquired pneumonia causes
Community-acquired pneumonia develops when infectious agents enter the lungs and trigger inflammation in the air sacs (alveoli). The most common causes are bacteria, viruses, and, less often, fungi. Bacterial CAP is often linked to Streptococcus pneumoniae, Haemophilus influenzae, or Mycoplasma pneumoniae, while viral cases may stem from influenza, RSV, or SARS-CoV-2.
People at higher risk include young children, older adults, smokers, and those with weakened immune systems or chronic illnesses like asthma or COPD. Environmental factors such as air pollution and poor living conditions can also increase susceptibility.
Transmission occurs through respiratory droplets when an infected person coughs or sneezes. Once inside the lungs, these pathogens multiply, causing inflammation, fluid build-up, and impaired oxygen exchange. Preventive measures include vaccination, good hygiene, and avoiding close contact with sick individuals.
When it’s diagnosed
Community-acquired pneumonia is diagnosed in 5–12% of adults who present to GPs with a lower respiratory tract infection.
Symptoms of Community-acquired Pneumonia
Some symptoms of CAP include:
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- Confusion, especially in the elderly
- Excess sweating and clammy skin
- Headache
- Loss of appetite, low energy, and fatigue
- Sharp or stabbing chest pain that worsens when breathing deeply or coughing
When it’s treated
The British Thoracic Society has developed a CAP Care Bundle that describes actions to take within four hours of a patient being admitted to secondary care. These actions include administering oxygen, assessing a chest x-ray, and administering antibiotics.
When CAP is more common
Community-acquired pneumonia is more common during the winter months and in older adults, but it can affect people of any age.
When Community-acquired pneumonia is fatal
Mortality rates for Community-acquired pneumonia vary depending on where the patient is treated. In the UK, mortality is less than 1% for patients managed in the community, between 5.7 and 14% for patients admitted to hospital, and over 30% for patients admitted to an intensive care unit
Risk Factors of CAP
Risk factors for CAP include:
- Age over 65
- Residence in a healthcare setting
- COPD
- Exposure to cigarette smoke
- Alcohol abuse
- Poor oral hygiene
- Use of acid-reducing drugs
- Contact with children
- Diabetes mellitus
- Chronic renal disease
How is community-acquired pneumonia CAP is transmitted
Community-acquired pneumonia (CAP) is primarily transmitted through inhaling respiratory droplets produced when an infected person coughs or sneezes, meaning the germs are spread directly from person to person through the air; essentially, you breathe in the bacteria or virus that is released when someone with pneumonia coughs or sneezes near you.