Chlamydia pneumoniae is a bacterium that can infect the respiratory tract. It can cause sore throat, bronchitis and pneumonia. The older term TWAR has been used for this organism, but Chlamydia pneumoniae is the standard medical name.
Symptoms
Symptoms often develop gradually and may include:
- sore throat or hoarseness
- runny or stuffy nose
- cough that can persist for several weeks
- headache
- tiredness
- low-grade fever
- chest discomfort
Some people develop pneumonia. Symptoms and severity vary, and infection can occur at any age.
How It Spreads
The bacterium spreads mainly through respiratory droplets and close contact with an infected person. Outbreaks can occur where people spend prolonged time together, including households, schools and other group settings.
Diagnosis
A clinician may diagnose a respiratory infection from the symptoms and examination. Testing for C. pneumoniae is not required for every mild respiratory illness, but laboratory testing may be considered in selected cases or during an outbreak.
Treatment
Many respiratory infections are mild. Rest, adequate fluids and symptom relief may be sufficient while the illness improves. When bacterial pneumonia caused by C. pneumoniae is diagnosed or strongly suspected, a clinician may prescribe an appropriate antibiotic. Antibiotics should be used only when medically indicated.
When to Seek Medical Care
Arrange medical assessment for worsening symptoms, persistent fever, significant chest pain, a cough that is not improving, or shortness of breath. Seek urgent medical care for severe breathing difficulty, confusion, blue or gray discoloration of the lips or skin, collapse, or rapidly worsening illness.
Related Topics
Sources and Further Reading
Last reviewed: 4 September 2026. This information does not replace individual medical assessment or treatment.