AUTHOR AND EDITOR INFORMATION

Section 1 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Acknowledgments
• References

INTRODUCTION

Section 2 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Acknowledgments
• References

Background

Mycoplasma pneumoniae is a common cause of community-acquired pneumonia, and, usually, the disease has a prolonged, gradual onset. M pneumoniae was first isolated in cattle with pleuropneumonia in 1898. In 1938, Reimann described the first cases of mycoplasmal pneumonia in man. Reimann coined the term "primary atypical pneumonia" after observing 7 patients in Philadelphia with marked constitutional symptoms, upper and lower respiratory tract symptoms, and a protracted course with gradual resolution. Peterson discovered the phenomenon of cold agglutinin in 1943, and high titers of cold agglutinins in patients with this type of pneumonia were discovered accidentally. In 1944, Eaton was credited with discovering a specific agent, coined Eaton's agent, as the principal cause of primary atypical pneumonia. First thought to be a virus, Eaton's agent was proved to be a Mycoplasma species in 1961.

For more information, see Medscape's Pneumonia Resource Center.

For a CME/CE activity, see CME/CE - Macrolides Improve Outcomes Among Elderly With Bacteremic Pneumonia.

Pathophysiology

The responsible organism, M pneumoniae, is a pleomorphic organism that, unlike bacteria, lacks a cell wall, and unlike viruses do not need a host cell for replication. The prolonged paroxysmal cough seen in this disease is thought to be due to the inhibition of ciliary movement. The organism has a remarkable gliding motility and specialized filamentous tips end that allows it to burrow between cilia within the respiratory epithelium, eventually causing sloughing of the respiratory epithelial cells.

The organism has two properties that seem to correlate well with its pathogenicity in humans. The first is a selective affinity for respiratory epithelial cells, and the second is the ability to produce hydrogen peroxide, which is thought to be responsible for much of the initial cell disruption in the respiratory tract and for damage to erythrocyte membranes.

The pathogenicity of M pneumoniae has been linked to the activation of inflammatory mediators, including cytokines.

Frequency

United States

M pneumoniae is now recognized as one of the most common causes of community-acquired pneumonia in otherwise healthy patients younger than 40 years, with the highest rate in 5- to 20-year olds. M pneumoniae causes upper and lower respiratory illness in all age groups, particularly in temperate climates, and in summer, may cause up to 50% of all pneumonias.

Mycoplasmal pneumonia can occur at any time of the year, but large outbreaks tend to occur in the late summer and fall. The incubation period tends to be smoldering and averages 3 weeks, in contrast to that of influenza and other viral pneumonias, which generally is a few days. Epidemics of mycoplasmal pneumonia tend to occur every 4-8 years in the general population and tend to be more frequent within closed populations, such as in military and prison populations. Although M pneumoniae is a common cause of pneumonia, only 5-10% of infected patients actually develop pneumonia.

Mortality/Morbidity

In almost all patients, the pneumonia resolves without any serious complications. M pneumoniae can cause severe pneumonia in children and has recently been associated with acute chest syndrome in patients with sickle cell anemia.   

Race

No racial predilections exist in mycoplasmal diseases.

Sex

No difference in disease frequency exists between males and females, but illnesses are somewhat more severe in males.  

Age

Mycoplasmal pneumonia is common in all age groups; however, it is most common in the first 2 decades of life and is rare in children younger than 5 years.

CLINICAL

Section 3 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Acknowledgments
• References

History

Mycoplasmal pneumonia is a disease of gradual and insidious onset of several days to weeks. The patient's history may include the following:

• Fever
• Malaise
• Persistent, slowly worsening dry cough; absence of cough makes the diagnosis of M pneumoniae unlikely
• Headache
• Chills, not rigors
• Scratchy sore throat
• Sore chest and tracheal tenderness (result of the protracted cough)
• Pleuritic chest pain (rare)

Physical

Most cases of pneumonia due to M pneumoniae resolve after several weeks, although a dry cough can be present for as long as a month; some patients can have a protracted illness lasting as long as 6 weeks. Other findings may also include the following:

• A nontoxic general appearance
• Erythematous tympanic membranes or bullous myringitis in patients older than age 2 years, an uncommon but unique sign
• Mild pharyngeal injection with minimal or no cervical adenopathy, but no exudate
• Normal lung findings with early infection but rhonchi, rales, and/or wheezes several days later
• Various exanthems including erythema multiforme and Stevens-Johnson syndrome

Causes

• The causative agent is M pneumoniae, a bacterium lacking a cell wall, which belongs to the class Mollicutes, the smallest known free-living microorganisms.
• Because the organism can be excreted from the respiratory tract for several weeks after the acute infection, isolation of the organism may not indicate acute infection.

DIFFERENTIALS

Section 4 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Acknowledgments
• References

Other Problems to be Considered

Chlamydia pneumoniae
Legionella pneumophila
Chlamydia psittaci
Chlamydia trachomatis
Coxiella burnetii (Q fever)

WORKUP

Section 5 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Acknowledgments
• References

Lab Studies

• The WBC count generally is not helpful, since results may be normal or elevated. Hemolytic anemia has been described, but it is rare.
• Sputum Gram stains and cultures usually are not helpful, since M pneumoniae lacks a cell wall and cannot be stained. 
• Elevated erythrocyte sedimentation rates may be present but are nonspecific.

Imaging Studies

• Radiographic findings are variable, but abnormalities are usually more striking than the findings on physical examination. 
• • Bronchopneumonia often involves a single lower lobe. Lobar consolidation is rare.
  • Platelike atelectasis is noted as thin, flat areas of collapsed lung and often is seen on a lateral image of the chest.
  • Reticulonodular or interstitial infiltrates, primarily in the lower lobes, may resemble other diseases with granulomatous pathology, such as tuberculosis, mycoses, and sarcoidosis. 
  • Hilar adenopathy sometimes is mistaken for malignancy.
  • Pleural effusions develop in fewer than 20% of patients; when present, they can be seen on lateral decubitus films.
• High-resolution CT scans of the chest are more sensitive than chest radiography in elucidating lung disease.

Other Tests

• M pneumoniae is difficult to culture and requires 7-21 days to grow; culturing is successful in only 40-90% of cases and does not provide information to guide patient management.
• Serology tests that demonstrate a 4-fold or greater increase or decrease in paired sera titers or a single titer greater than or equal to 1:32
• • Serum cold agglutination is a nonspecific test for M pneumoniae, but findings are positive in 50-70% of patients after 7-10 days of infection. Cold agglutinin tests can be obtained from diagnostic laboratories. A negative result does not exclude infection, and this test may be affected by cross-reactions with other pathogens, such as adenovirus, Epstein-Barr, and measles viruses. A quick bedside test can be performed by partially filling a purple-top tube with blood and placing it in ice; a positive finding is one in which "grains of sand" appear on the glass portion of the tube.
  • Other serological tests include complement fixation, enzyme-linked immunoassay, and indirect hemagglutination. All of these have acceptable sensitivity and specificity.
• Polymerase chain reaction
• • Polymerase chain reaction (PCR) has been shown to accurately diagnose atypical pneumonia and has been used for epidemiologic studies, but it is currently not used in most clinical settings. Real-time PCR is a promising test that allows detection of M pneumoniae DNA in all phases of infection, including early periods when the serum may be negative for antibody.
  • A radiolabeled DNA probe detects M pneumoniae ribosomal RNA in respiratory secretions with 90% sensitivity.
  • Eosinophil cationic protein (ECP) has been studied in M pneumoniae infection and asthma and may show some promise. ECP measures damage to the respiratory epithelium.

TREATMENT

Section 6 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Acknowledgments
• References

Emergency Department Care

Mycoplasmal pneumonia should be considered as a possible etiology in any emergency department patient presenting with 3 weeks of a steadily progressive cough. Patients are usually not critically ill, but seek relief from the persistent, worsening cough. Occasionally, various pulmonary and extrapulmonary complications may occur and may require emergent attention.

MEDICATION

Section 7 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Acknowledgments
• References

Several antimicrobials are effective in reducing the length of illness due to mycoplasmal pneumonia.

Drug Category: Antibiotics

Empiric antimicrobial therapy must be comprehensive and should cover all likely pathogens in the context of the clinical setting. In the treatment of mycoplasmal pneumonia, antimicrobials against M pneumoniae are bacteriostatic, not bactericidal.

FOLLOW-UP

Section 8 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Acknowledgments
• References

Further Inpatient Care

• If patients with pneumonia due to M pneumoniae require admission, use of standard and droplet precautions are recommended for the duration of the illness.

Further Outpatient Care

• Antibiotic prophylaxis for exposed contacts is not routinely recommended. However, macrolide or doxycycline prophylaxis should be used in households in which patients with underlying conditions may be predisposed to severe mycoplasmal infection, such as those with sickle cell disease or antibody deficiencies.

Complications

• Lobar consolidation
• Abscess
• Bronchiolitis obliterans
• Necrotizing pneumonitis
• Acute respiratory distress syndrome
• Respiratory failure
• Extremely rare extrapulmonary complications include the following: myocarditis, pericarditis, conduction abnormalities, encephalitis, Guillain-Barré syndrome, peripheral neuropathy, transverse myelitis, hemolytic anemia, coagulopathies, erythema multiforme, macular exanthems, vesicular exanthems, erythema nodosum, and urticaria.

Prognosis

• With proper treatment, a full recovery is expected.

ACKNOWLEDGMENTS

Section 9 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Acknowledgments
• References

The authors and editors of eMedicine gratefully acknowledge the contributions of previous author, Santos Cantu Jr, MD, to the development and writing of this article.

REFERENCES

Section 10 of 10

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Acknowledgments
• References

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Article Last Updated: Aug 5, 2008