Atypical Pneumonia

woman sneezing, label: Chlamydia pneumoniae Infection

Chlamydia pneumoniae Infection

Couple relaxing in a hot tub, label: Legionnaires' Disease

Legionnaires’ Disease

Girl blowing nose, label: Mycoplasma pneumoniae Infection

Mycoplasma pneumoniae Infection

Parakeet, label: Psittacosis


Pneumonia is an infection of the lungs that viruses, bacteria, and fungi can cause. A common cause of typical bacterial pneumonia is Streptococcus pneumoniae. Before modern diagnostic tests were available, researchers noticed that some pneumonias had different characteristics compared to “typical” pneumonias, such as

  • Caused slightly different symptoms than typical pneumonia
  • Appeared different on a chest X-ray than typical pneumonia or
  • Responded differently to antibiotics that were used for typical bacteria

They called these “atypical”. Now researchers usually consider bacteria as being “atypical” if they are hard to detect through standard bacterial methods. These “atypical” bacteria include

  • Chlamydia pneumoniae
  • Chlamydia psittaci
  • Legionella pneumophila
  • Mycoplasma pneumoniae

Even though these infections are called “atypical,” they are not uncommon.


Common Types of Pneumonia Caused by Atypical Bacteria
  • Chlamydia pneumoniae Infection
    This illness, caused by Chlamydia pneumoniae, is most common in school-aged children and usually develops into mild pneumonia or bronchitis…
  • Psittacosis
    People get this sometimes serious illness, caused by Chlamydia psittaci, from infected pet birds (parrots, parakeets) and poultry (turkeys, ducks)…
  • Legionnaires’ Disease
    Legionnaires’ disease is a severe type of pneumonia that is caused by a type of bacteria called Legionella
  • Mycoplasma pneumoniae Infection
    This generally mild illness is a common cause of “walking pneumonia”…

How Do You Say That?

Find pronunciation guides below for common words associated with atypical pneumonia.

  • Bronchitis — brahn-KITE-uss
  • Chlamydia — klah-MID-e-a
  • Legionella — lee-juh-NELL-a
  • Legionnaires — lee-juh-NAIRS
  • Mycoplasma — MY-ko-plaz-ma
  • Pneumonia — noo-MOAN-yah
  • Pneumoniae — noo-MOAN-e-a
  • Psittaci — SIT-ah-see
  • Psittacosis — sit-ah-KOH-sis
  • Pneumophila — noo-MAH-fil-ah
  • Streptococcus — strep-toe-KAH-kuss
  • Tracheobronchitis — TRAY-key-o-brahn-KITE-uss
Page last reviewed: October 1, 2019