Key points
- Bacteria and viruses are common causes of pneumonia (a lung infection).
- Fungi and parasites are less common causes.
- Germs that commonly cause pneumonia in the community are different from those in healthcare settings.
- Clinicians aren't always able to find out which germ caused someone to get sick with pneumonia.
Overview
Pneumonia is an infection of the lungs. Many germs (bacteria, fungi, parasites, and viruses) can cause pneumonia.
Types
People in the community and people in healthcare settings may be exposed to different types of bacteria and viruses.
Defining types of pneumonia
Community-acquired pneumonia is when someone develops pneumonia in the community (not in a hospital).
Healthcare-acquired pneumonia is when someone develops pneumonia during or following a stay in a healthcare setting.
Ventilator-associated pneumonia is when someone gets pneumonia after being on a ventilator, a machine that supports breathing.
Symptoms
Common symptoms of pneumonia include:
- Chest pain when breathing or coughing
- Altered mental status (confusion)
- Cough
- Fatigue (feeling tired)
- Fever or chills
- Nausea, vomiting, or diarrhea
- Shortness of breath
Who is at risk
Some people are at increased risk for pneumonia due to age, other health conditions, and certain behaviors.
Causes
Bacterial infections
Bacterial infections that are common causes of community-acquired pneumonia include:
The following bacterial infections can cause pneumonia, but are less common causes:
- Chlamydia pneumoniae infection
- Haemophilus influenzae disease
- Legionella infection (Legionnaires' disease and Pontiac Fever)
- Pertussis (whooping cough)
- Psittacosis
Fungal infections
In general, fungal infections are a less common cause of pneumonia.
Viral infections
Viral infections that commonly cause pneumonia include
- COVID-19
- Human metapneumovirus (HMPV) infection
- Human parainfluenza virus (HPIV) infection
- Influenza (flu)
- Respiratory syncytial virus (RSV) infection
- Rhinovirus infection
The following viral infections can cause pneumonia, but are a less common cause:
Sometimes the cause of pneumonia is unknown
Prevention
Pneumonia affects millions of people worldwide each year.
People can lower their risk of pneumonia with immunizations and other healthy living practices.