DefinitionAtypical pneumonia refers to pneumonia caused by certain bacteria, including Legionella pneumophila, Mycoplasma pneumoniae, and Chlamydophila pneumoniae. It is called “atypical” because the symptoms differ from those of pneumonia due to other common bacteria. Pneumonia is an infection of the lung.
Alternative NamesWalking pneumonia; Chlamydophila pneumoniae; Community-acquired pneumonia - atypical
Causes, incidence, and risk factorsMycoplasma pneumonia is a type of atypical pneumonia. It is caused by the bacteria M. pneumoniae. It typically affects people younger than age 40. For more information on this type of pneumonia, see: Mycoplasma pneumoniaPneumonia due to chlamydia-related bacteria occurs year round and accounts for 5 - 15% of all pneumonias. It is usually mild.Pneumonia due to Legionella is seen more often in middle-aged and older adults, smokers, and those with chronic illnesses or a weak immune system. It can be more severe.See also: Legionnaire's disease
SymptomsPneumonia due to mycoplasma and chlamydophila bacteria is usually mild.Pneumonia due to Legionella pneumophila gets worse during the first 4 - 6 days, and then improves over 4 - 5 days.Even though symptoms will improve, it may take a while for them to go away completely.The most common symptoms of pneumonia are:ChillsCough (with Legionella pneumonia, you may cough up bloody mucus)Fever, which may be mild or highShortness of breath (may only occur when you climb stairs)Other symptoms include:Chest pain that gets worse when you breathe deeply or coughConfusion, especially in older people or those with Legionella pneumoniaHeadacheLoss of appetite, low energy, and fatigueMuscle aches and joint stiffnessSweating and clammy skinLess common symptoms include:Diarrhea (especially with Legionella pneumonia)Ear pain (with mycoplasma pneumonia)Eye pain or soreness (with mycoplasma pneumonia)Neck lump (with mycoplasma pneumonia)Rash (with mycoplasma pneumonia)Sore throat (with mycoplasma pneumonia)
Signs and testsPersons with suspected pneumonia should have a complete medical evaluation. It may be hard for your health care provider to tell whether you have pneumonia or bronchitis, so you may need a chest x-ray. Depending on the severity of the illness, other tests may be done, including:Arterial blood testComplete blood count (CBC)Blood culturesBlood tests to identify the bacteriaBronchoscopy (rarely needed)CT scan of the chestOpen lung biopsy (only done in very serious illnesses when the diagnosis cannot be made from other sources)Sputum cultureUrine test to check for Legionella bacteria Urine tests or a throat swab may also be done.
TreatmentTake these steps at home:Control your fever with aspirin, nonsteroidal anti-inflammatory drugs (NSAIDs, such as ibuprofen or naproxen), or acetaminophen. DO NOT give aspirin to children.Do not take cough medicines without first talking to your doctor. Cough medicines may make it harder for your body to cough up the extra sputum.Drink plenty of fluids to help loosen secretions and bring up phlegm.Get a lot of rest. Have someone else do household chores.Antibiotics are used to treat atypical pneumonia.You may be able to take antibiotics by mouth at home.If you have severe atypical pneumonia, you will likely be admitted to a hospital, where you will be given antibiotics through a vein (intravenously), as well as oxygen.Antibiotics are used for 2 weeks or moreAntibiotics used to treat atypical pneumonia include:AzithromycinClarithromycinErythromycinFluoroquinolones (such as levofloxacin)Tetracyclines (such as tetracycline or doxycycline)
Expectations (prognosis)Most patients with pneumonia due to mycoplasma or chlamydophila do well with the right antibiotics. Legionella pneumonia can be severe, leading to problems in patients with kidney failure, diabetes, COPD, and a weak immune system. It can lead to death.
ComplicationsBrain and nervous system infections, such as meningitis, myelitis, and encephalitisHemolytic anemia, a condition in which there are not enough red blood cells in the blood because the body is destroying themSevere lung damage
Calling your health care providerContact your health care provider if you develop fever, cough, or shortness of breath. There are numerous causes for these symptoms. The doctor will need to rule out pneumonia.
PreventionWash your hands often and have other people around you do the same.If your immune system is weak, stay away from crowds. Ask visitors who have a cold to wear a mask.Get a flu shot every year. Ask your doctor if you need a pneumonia vaccine.
ReferencesLimper AH. Overview of pneumonia. In: Goldman L, Schafer AI,eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 97.Mandell LA, Wunderink RG, Anzueto A, et al. InfectiousD iseases Society of America/American Thoracic Society consensus guidelines on the management of community-acquired pneumonia in adults. Clin Infect Dis. 2007;44:S27-S72.Torres A, Menendez R, Wunderink R. Pyogenic bacterial pneumonia and lung abscess. In: Mason RJ, VC Broaddus, Martin TR, et al, eds. Murray and Nadel’s Textbook of Respiratory Medicine. 5th ed. Philadelphia, Pa:Saunders Elsevier; 2010:chap 32.