Mycoplasma Pneumonia

Article Author:
Basma Abdulhadi
Article Editor:
John Kiel
Updated:
5/5/2019 11:26:35 PM
PubMed Link:
Mycoplasma Pneumonia

Introduction

Mycoplasma pneumonia is a bacteria that can infect humans. It usually causes upper respiratory tract infections, but can also cause pneumonia, and it is one of the most common causes of atypical pneumonia in the United States. Many extrapulmonary infections have been attributed to Mycoplasma pneumoniae infections. However, a causal link is yet to be established.[1][2][3]

Etiology

Mycoplasma species are the smallest living organisms that can survive alone in nature. There are over 120 Mycoplasma species; only 13 have been isolated from humans, and only 4 are known to cause disease in humans. Mycoplasma pneumoniae is the pathogen most commonly associated with disease in humans. It is a short rod with no cell wall; therefore, it is not visible on Gram stain. It can be isolated on media supplemented with serum. However, it is fastidious, and isolation is not usually performed in clinical laboratories.[4]

Epidemiology

M. pneumoniae is transmitted from person to person via respiratory droplets during close contact. It has an incubation period that ranges between 2 to 3 weeks. Like most respiratory pathogens, infection usually occurs during winter months but can happen year round. Estimates show that around 1% of the population of the United States is infected annually. Incidence may be much higher since infection can subclinical or cause milder disease that does not require hospitalization. Outbreaks of mycoplasma infection occur in military recruits, hospitals, nursing homes, and other long-term care facilities.[5][4]

Pathophysiology

Many M. pneumoniae infections are asymptomatic. The onset of the illness is usually gradual and includes a headache, malaise, and low-grade fever. Most patients who acquire this infection do not develop pneumonia. A cough associated with this infection is incessant and usually nonproductive. Chest soreness from coughing is common. Wheezing can also occur. Other respiratory symptoms include pharyngitis, rhinorrhea, and ear pain. Pleural effusion occurs in 15% to 20% of patients who develop pneumonia and may predict increased morbidity and mortality.  Most cases of pneumonia are mild and self-limited. However, a more fulminant course can occur. Extrapulmonary features may help suggest the diagnosis and include hemolysis, skin rash, joint pain, gastrointestinal (GI) symptoms, as well as heart disease. These occur in less than 5% to 10% of patients. Hemolysis occurs due to IgM antibodies producing a cold agglutinin reaction. Cardiac involvement includes conduction abnormalities on ECG, congestive heart failure, and chest pain.

Toxicokinetics

M. pneumoniae has adherence proteins that can attach to epithelial membranes; particularly the respiratory tract epithelium. Once attached, M. pneumoniae produces hydrogen peroxide and superoxide, causing injury to epithelial cells and their associated cilia. Antibodies produced against M. pneumoniae may act as autoantibodies since they crossreact with human brain cells and RBCs, are cold agglutinins. 

History and Physical

Patient symptoms are typically more significant than objective findings on physical exam. Disease onset is gradual, and patients can initially complain of a headache and low-grade fever. A nagging cough is usually the most prominent respiratory feature. Physical examination findings are often minimal. Chest auscultation can be normal even if pneumonia is present. Scattered rales, wheezes can present later in the course of the disease. Sinus tenderness and mild erythema of the posterior pharynx, as well as the tympanic membrane, may also be found on physical examination. A mild erythematous maculopapular or vesicular rash may also be found.

Evaluation

There are no specific clinical or radiological findings to mycoplasma pneumonia that can differentiate it from other causes of atypical pneumonia. Patients, however, tend to have a more gradual onset of disease, more multisystem involvement, and a normal white blood cell (WBC) count. Patients usually present in an outpatient setting, and microbial diagnosis is not usually performed for outpatients with community-acquired pneumonia since empiric treatment is usually successful. When available, PCR can be done rapidly and is the test of choice. Testing for cold agglutinins can sometimes be used to support a clinical diagnosis when a rapid diagnosis must be made. M. pneumoniae lacks a cell wall and is fastidious therefore gram stain and cultures are not useful for the diagnosis of these organisms.[6][7]

Hemolysis is found in the majority of patients with pneumonia and causes a positive Coomb's test and an elevated reticulocyte count. Cold agglutinin titers are elevated in more than 50% of patients with mycoplasma disease. However, this is not specific to Mycoplasma infections and can be found in patients with viral pneumonia, or infectious mononucleosis due to EBV or CMV. WBC count is normal in 75% to 90% of cases. The most common chest x-ray findings are a reticulonodular pattern or patchy areas of consolidation; these can be unilateral or bilateral and are more prominent in the lower lobes.[8][9]

Eosinophil cationic protein has been found to be elevated in patients with mycoplasma infection and asthma. It is believed that this protein damages the epithelium in the airways and induces hypersensitivity of the bronchial smooth muscle. However, more studies are required before its use as a diagnostic marker becomes universal.[10]

Treatment / Management

Gradual onset of symptoms combined with extrapulmonary involvement as well as a normal WBC count points to atypical pneumonia. Most patients with M. pneumoniae pneumonia present in outpatient settings and treatment is often with empiric antibiotics for atypical pneumonia. Note that many patients may undergo a period of symptomatic management before seeking medical attention and/or receiving antibiotic treatment.

Treatment of M. pneumoniae includes macrolides, doxycycline, or fluoroquinolones. Azithromycin is the most frequently used antibiotic and is usually prescribed for 5 days (500 mg for the first dose, followed by 250 mg daily for 4 days). Patients receiving doxycycline or fluoroquinolones should be given 7 to 14 days of treatment.[11][12]

Differential Diagnosis

Diagnostic Considerations

M.pneumoniae is a very common cause of community-acquired pneumonia in healthy individuals under the age of 40. Large outbreaks are known to occur in the late summer months and early fall. The infection is also more common in populations that live in close quarters like prisoners and military personnel. Unlike other viral pneumonia, the incubation period for mycoplasma is 14-21 days. The key feature to the diagnosis is the absence of a wet cough. Other diagnoses that can be confused with mycoplasma pneumonia include the following:

  • Aspiration Pneumonitis and Pneumonia
  • Bacterial Pneumonia
  • Chlamydia pneumoniae
  • Coxiella burnetii infection
  • Empyema
  • Legionella pneumophila
  • Lung abscess
  • Pediatric Pneumonia
  • Q Fever
  • Viral Pneumonia

Prognosis

In the majority of patients who are promptly treated, prognosis is excellent and patients are expected to make a full recovery. The symptoms and signs of pneumonia usually resolve within a few days without any complications. However in young children, the infection can be associated with severe pneumonia and in patients with sickle cell anemia, it may be associated with acute chest syndrome. The immunity after a Mycoplasma pneumoniae infection is short lived.

Complications

Even though mycoplasma pneumonia in most people is a benign infection, it can lead to a number of complications, especially in children and the elderly. The list of complications includes the following:

  • ARDS
  • Bronchiolitis obliterans
  • Lobar consolidation
  • Lung abscess
  • Necrotizing pneumonitis
  • Pleural effusion (15% to 20%), empyema (rare)
  • Respiratory failure

Extrapulmonary Complications

Mycoplasma can also be associated with severe extrapulmonary complications. These complications may be due to the organism itself it may be triggered by the resulting immunological response to the bacteria. The list of extrapulmonary complications includes:

  • Myocardium problems: Conduction abnormalities, heart blocks or rhythm disturbances. Both pericarditis and congestive heart failure have been reported in young people.
  • Central nervous system (CNS): Rare but can include encephalitis, transverse myelitis, aseptic meningitis and cerebellar ataxia. These CNS complications are more common in children.
  • Hematologic problems: Hemolytic anemia due to cross-reactivity of antibodies to M. Pneumoniae antigens to red blood cells. The hemolysis is mild.
  • Dermatology: M. Pneumoniae infection may be associated with urticaria, erythema nodosum or steven johnson syndrome. The skin lesions are seen in about one-third of patients.
  • Musculoskeletal problems include myalgia and arthralgia. Septic arthritis is very rare. Rare cases of rhabdomyolysis have been reported.
  • Gastrointestinal (GI) dysfunction include pancreatitis or hepatitis and are linked to the circulating IgM antibodies.
  • Ophthalmologic problems include conjunctivitis, optic papillitis, anterior uveitis and cranial neuropathies.
  • Kidney problems are rare and may result in glomerulonephritis as result of immune complex precipitation in the glomeruli.

Pearls and Other Issues

  • Mycoplasma pneumoniae is a common cause of pneumonia
  • Prodromal symptoms include headache and fever and patients subsequently develop a dry cough
  • It is frequently subclinical and thus underdiagnosed due to lack of symptoms or specific diagnostic criteria
  • Chest radiograph often does not show an infiltrate
  • Management is with antibiotics, generally azithromycin
  • Children, the elderly and individuals with sickle cell disease are at risk of complications

As for prevention of infection, there are currently no vaccines for M. pneumoniae. Several studies looked at the efficacy of azithromycin prophylaxis in military training facilities and other closed settings. However, there are still no recommendations for these practices. Hospitalized patients with M. pneumoniae infection should be placed on droplet precautions for the full duration of their illness.

Enhancing Healthcare Team Outcomes

Mycoplasma pneumonia is often encountered by the primary care provider, nurse practitioner, emergency department physician and the internist. Because there are no rapid tests to detect this organism, most patients are treated empircally. The pneumonia is benign and most patients have an uneventful recovery. However, some patients may develop a parapneumonic effusion, otitits media, lung abscess or an empyema. These patients are best referred to the appropriate specialty for further management. In immuncompromised and transplant patients, an infectious disease consult should be made.[13]


References

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