[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [Intracellular and atypical bacteria](https://durgical.com/en/microbiology/groups/intracellular-and-atypical-bacteria/) › Chlamydia pneumoniae / Chlamydia psittaci

[Microbiology](https://durgical.com/en/microbiology/) · [Intracellular and atypical bacteria](https://durgical.com/en/microbiology/groups/intracellular-and-atypical-bacteria/)

# Chlamydia pneumoniae / Chlamydia psittaci

- Bacterium
- Gram-negative
- Exam priority: medium

Two chlamydiae that cause atypical pneumonia: one passes between people by coughing; the other comes from birds such as parrots and pigeons.

Updated 2026-11-01

Also called: respiratory chlamydiae, psittacosis

## Key points

- Pneumonia + parrot or pigeon = psittacosis
- Atypical pneumonia: dry cough, mild fever, X-ray worse than the patient looks
- Doxycycline or a macrolide; not beta-lactams

## At a glance

**Gram**
Gram-negative

**Shape**
Small coccobacilli

**Oxygen**
Obligate intracellular

**Family**
Chlamydiaceae

**Stain**
Not seen on Gram; molecular or serological diagnosis

## Morphology

- Same elementary body–reticulate body cycle as C. trachomatis
- Inclusions without glycogen (do not stain with iodine)

## Transmission

- C. pneumoniae: respiratory droplets from person to person
- C. psittaci: inhalation of dust from dried bird droppings or secretions
- Psittacosis rarely passes between people

**Reservoir:** C. pneumoniae: humans; C. psittaci: parrots, parakeets, pigeons, poultry

### Isolation precautions

What the care team adds to standard precautions.

- Standard

## Virulence factors

- Infect respiratory epithelial cells and macrophages
- C. psittaci spreads through blood to the liver and spleen

## Diseases it causes

- Atypical community-acquired pneumonia [Community-acquired pneumonia →](https://durgical.com/en/conditions/community-acquired-pneumonia/)
- Pharyngitis, sinusitis, bronchitis; psittacosis with high fever and headache

## Clinical picture

- Gradual onset: sore throat, hoarseness and persistent dry cough
- Psittacosis: high fever, severe headache, dry cough, sometimes relative bradycardia and splenomegaly
- The X-ray often looks worse than the examination suggests

## Diagnosis

- PCR on nasopharyngeal swab or sputum (respiratory panels)
- Serology with paired samples
- History of bird contact: the key to psittacosis

## Treatment

Tetracyclines (doxycycline) or macrolides (azithromycin); respiratory fluoroquinolones are an alternative. Beta-lactams do not work.

Drug class only; doses and regimens are set by the clinician from the current guideline.

In Pharmacology:

- [Doxycycline](https://durgical.com/en/pharmacology/doxycycline/)
- [Azithromycin](https://durgical.com/en/pharmacology/azithromycin/)

## Prevention

- Handwashing and cough hygiene
- Wet cleaning of cages, respiratory protection when handling sick birds

## Memory aid

«Psittacus» is Latin for parrot: if the pneumonia patient owns a sneezing parrot, the bird has already given the answer.

## Test yourself

Think of the answer, then tap the question to see it.

## How is C. psittaci acquired?

By inhaling dust from dried droppings or secretions of infected birds.

## Which antibiotic classes treat chlamydial pneumonia?

Tetracyclines such as doxycycline and macrolides such as azithromycin.

## How is C. pneumoniae transmitted?

From person to person by respiratory droplets when coughing or sneezing.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/microbiology/chlamydia-pneumoniae-chlamydia-psittaci/)

## Related

- [Chlamydia trachomatis](https://durgical.com/en/microbiology/chlamydia-trachomatis/)
- [Mycoplasma pneumoniae](https://durgical.com/en/microbiology/mycoplasma-pneumoniae/)
- [Coxiella burnetii](https://durgical.com/en/microbiology/coxiella-burnetii/)

## Related conditions

- [Community-acquired pneumonia](https://durgical.com/en/conditions/community-acquired-pneumonia/)

## What the colours mean

**Gram-positive**
Thick peptidoglycan wall: stains purple.

**Gram-negative**
Thin wall with an outer membrane: stains pink.

**Acid-fast**
Lipid-rich wall (mycobacteria): Ziehl–Neelsen stain.

[← Back to the group: Intracellular and atypical bacteria](https://durgical.com/en/microbiology/groups/intracellular-and-atypical-bacteria/)

Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [About Chlamydia pneumoniae Infection | C. pneumoniae | CDC](https://www.cdc.gov/cpneumoniae/about/index.html) (Centers for Disease Control and Prevention (CDC), 2024); [About Psittacosis](https://www.cdc.gov/psittacosis/about/index.html) (Centers for Disease Control and Prevention (CDC), 2024).

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

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Source: https://durgical.com/en/microbiology/chlamydia-pneumoniae-chlamydia-psittaci/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/microbiology/chlamydia-pneumoniae-chlamydia-psittaci/