Janice Haney Carr CDC

Atypical Pneumonia

Healthy Lungs
Diseases & Conditions
Contributed bySubramanian Malaisamy MD, MRCP (UK), FCCP (USA)+1 moreAug 03, 2021

What are the other Names for this Condition? (Also known as/Synonyms)

  • Community-Acquired Pneumonia (causing Atypical Pneumonia)
  • Legionella pneumophila (causing Atypical Pneumonia)
  • Mycoplasma pneumoniae (causing Atypical Pneumonia) 

What is Atypical Pneumonia? (Definition/Background Information)

  • Atypical Pneumonia is a type of lung infection that is caused by specific types of bacteria, namely Legionella pneumophila, Mycoplasma pneumoniae, and Chlamydia pneumoniae
  • Individuals with Atypical Pneumonia often have mild signs and symptoms. They are able to carry on with their daily activities without much difficulties
  • This infection is more prevalent during summer and autumn (fall) seasons and uncommon during winters. It can occur as a Community-Acquired Pneumonia

Who gets Atypical Pneumonia? (Age and Sex Distribution)

  • Atypical Pneumonia can occur at any age; the affected age range depends on the type of bacteria causing the condition
    • Atypical Pneumonia caused by Mycoplasma pneumoniae bacteria generally affects individuals under the age of 40 years
    • Atypical Pneumonia caused by the bacteria Legionella pneumophila usually occurs in older individuals
  • Both males and females are affected
  • The infection is seen worldwide among all races and ethnic groups. It is termed Community-Acquired Pneumonia and is known to cause local epidemics

What are the Risk Factors for Atypical Pneumonia? (Predisposing Factors)

The risk factors for Atypical Pneumonia include the following:

  • Chronic smoking, since smoking affects the immune system of the lungs
  • Individuals with chronic illnesses and those who have weakened immune systems
  • Chronic steroidal therapy and immunosuppressive therapy
  • Overcrowded conditions: The disease spreads more easily in closed and ill-ventilated spaces such as dormitories
  • Atypical Pneumonia may be caused by Legionella pneumophila bacteria, which can grow in waterbodies such as water tanks. The use of this contaminated water in air conditioning units and humidifiers can cause infection in individuals who breathe in the infected air

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases ones chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Atypical Pneumonia? (Etiology)

  • Atypical Pneumonia is a bacterial infection caused by specific types of bacteria, namely Legionella pneumophila, Mycoplasma pneumoniae, and Chlamydia pneumoniae, present in lungs
  • This bacterial infection can spread from one individual to another through infected air droplets, when the infected individuals cough or sneeze

What are the Signs and Symptoms of Atypical Pneumonia?

The signs and symptoms of Atypical Pneumonia include:

  • In a majority of the individuals, Atypical Pneumonia causes chills, cough, fever, and shortness of breath. Shortness of breath can occur from activities such as running, climbing up the stairs, or swimming
  • Other symptoms that occur less commonly include chest pain, confusion (mostly in elderly adults), headaches, lack of energy, hunger, joint stiffness, and increased sweating
  • Symptoms that occur rarely include diarrhea, ear and eye pain, rashes, neck lumps, and sore throat
  • In general, the symptoms may improve after 4 days, but complete recovery can take up to 2 weeks
  • Individuals with severe cases of Atypical Pneumonia, may take much longer to recover

How is Atypical Pneumonia Diagnosed?

The healthcare provider should have a high index of suspicion for Atypical Pneumonia. This is especially important since the signs and symptoms may not be very prominent. The following methods are used to diagnose the lung infection:

  • A through physical examination and complete medical history
  • Chest X-ray may reveal the presence of pneumonia
  • Arterial blood gas indicates the level of oxygen in blood. Atypical Pneumonia can affect the level of oxygen in blood because of poor lung function
  • A complete blood count (CBC) reveals an increased amount of white blood cells, which is often a sign of infection
  • Sputum culture and blood cultures are helpful in determining the cause of pneumonia. It is important for the healthcare provider to communicate with the laboratory about the suspicion of Atypical Pneumonia. This is especially important, since the bacteria causing the infection requires special testing procedures in the laboratory
  • A bronchoscopy may be needed to help rule out other causes of pneumonia
  • CT scan of chest is also helpful in determining the extent of pneumonia
  • Serum and urine serology studies may help with the diagnosis of Atypical Pneumonia
  • In severe and rare cases of Atypical Pneumonia, an open lung biopsy may be performed to exclude other causes

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis. 

What are the possible Complications of Atypical Pneumonia?

In a majority of individuals, Atypical Pneumonia does not cause any significant complications. However, in others, the complications could include:

  • Atypical Pneumonia can spread from the lungs to the brain causing brain infection. This can result in severe headaches and confusion
  • In some rare cases, severe lung infection can cause permanent lung damage. In most of the individuals though, no prominent lung damage is noted
  • Some individuals may have a condition called hemolytic anemia. This is because Atypical Pneumonia bacteria can cause the formation of autoantibodies, which destroys the blood cells. The destruction of red blood cells results in anemia. In such cases, a complete treatment of Atypical Pneumonia will result in resolution of hemolytic anemia too

How is Atypical Pneumonia Treated?

The following treatment measures are generally used to treat Atypical Pneumonia:

  • Antibiotic therapy is typically the main treatment course. Symptomatic treatment measures may be used to alleviate pain and other symptoms of the infection
  • Over-the-counter medication for fever and cough can help improve one’s symptoms. It is important to note that taking over-the-counter medications should only be after due consultation with the healthcare provider
  • Plenty of rest and intake of fluids can help in a speedy recovery
  • In severe cases of Atypical Pneumonia, the lung function may be severely affected and hospitalization for administration of intravenous antibiotics and oxygen treatment may be necessary

How can Atypical Pneumonia be Prevented?

The following preventative measures can help arrest the spread of Atypical Pneumonia:

  • Frequently washing one’s hands
  • Avoiding contact with individuals affected by the condition where possible. This also includes avoiding visiting them in hospitals. This helps decrease the spread of infection within the community
  • Annual flu vaccination shots may help in boosting one’s immunity, and also help prevent post-flu pneumonias

What is the Prognosis of Atypical Pneumonia? (Outcomes/Resolutions)

  • In a majority of individuals, Atypical Pneumonia resolves without any complications, and a complete recovery is observed within about 2 weeks
  • Early diagnosis, complete rest, and appropriate antibiotic treatment can help result in excellent prognoses
  • In individuals with severe infection, Atypical Pneumonia can be complicated by residual lung and brain damage
  • Most types of Atypical Pneumonia do not lead to fatalities when early and appropriate antibiotics are used
  • Atypical Pneumonia caused by the bacteria Legionella pneumophila can be fatal in individuals with poor immune systems, severe diabetes, or with kidney failure

Additional and Relevant Useful Information for Atypical Pneumonia:

It is important to differentiate Atypical Pneumonia from other types of pneumonia. The concerned healthcare provider will determine the cause and type of pneumonia through appropriate testing.

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On the Article

Krish Tangella MD, MBA picture
Approved by

Krish Tangella MD, MBA

Pathology, Medical Editorial Board, DoveMed Team
Subramanian Malaisamy MD, MRCP (UK), FCCP (USA) picture
Reviewed by

Subramanian Malaisamy MD, MRCP (UK), FCCP (USA)

Associate Chief Medical Officer, Medical Editorial Board, DoveMed Team


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