What is mycoplasma pneumonia?

Definition

Mycoplasma pneumonia is a bacterial
infection of the lungs. The infection is considered an
atypical
pneumonia.

Causes

The etiologic agent is Mycoplasma pneumoniae, a bacterial species found to be widespread in the environment. This bacterium, which has no cell wall, can survive alone in the presence or absence of oxygen. It has a specialized tip (organelle) that provides motility and mediates bacterial interactions with its host cells. Moreover, adherence proteins allow M. pneumoniae to attach to the lining of the respiratory tract (from the nasal passage to the lungs), acting like a parasite on the surface of its host cells. The bacteria produce hydrogen peroxide and superoxide, substances that injure the respiratory lining.

Risk Factors

M. pneumoniae is transmitted through respiratory droplets between people. Persons who are in close contact are at highest risk for this infection and include those who live, work, or perform activities in crowded places, such as schools, homeless shelters, prisons, dormitories, military facilities, and hospitals. Other associated risk factors for Mycoplasma respiratory infection include smoking and lower levels of preexisting immunoglobulin G levels. There is no age or gender predilection for the disease.

Symptoms

The symptoms of Mycoplasma pneumonia gradually appear from one
to three weeks after infection. Symptoms may be divided into those of the
respiratory tract (pulmonary) versus those that have extrapulmonary manifestations
(cardiologic, neurologic, dermatologic, and others). The general symptoms include
malaise, fever, chills, and excessive sweating, which may precede the onset of
illness. The common pulmonary symptoms include nonproductive cough, runny nose,
and sore throat. Extrapulmonary symptoms may include chest pain, headache, eye
pain, muscle aches, joint stiffness, skin rash, and a breakdown of red blood
cells. Central nervous system involvement may manifest as encephalitis
and meningitis.

Screening and Diagnosis

A physician will obtain a medical history, perform a physical examination, and
evaluate the list of symptoms. A chest X ray will be ordered along with laboratory
studies (complete blood count and basic electrolytes). Other diagnostic tests
include blood cultures, sputum cultures, a urine test, and a throat swab. Serology
tests may also be obtained to evaluate the presence and levels of antibodies
against Mycoplasma antigens. Other nonroutine tests include
detection of Mycoplasma genetic material,
Mycoplasma antigens, or cold agglutinins. Depending on the
severity of the clinical presentation, a computed tomography (CT)
scan of the chest and bronchoscopy
(in which a thin fiberoptic scope is used to view the respiratory tract and the
lungs) may be performed. Open lung biopsy is done only in very serious illnesses
when the diagnosis is uncertain or the person’s symptoms are not resolving.

Treatment and Therapy

Antibiotic options against M. pneumoniae
include macrolides (such as azithromycin, clarithromycin,
anderythromycin), fluoroquinolones (such as levofloxacin and moxifloxacin), and
tetracyclines (such asdoxycycline). Adjunct therapies may be
necessary if extrapulmonary symptoms are present. For example, steroids have shown
benefit in treating children with neurologic disease.

Prevention and Outcomes

Antibiotic prophylaxis with azithromycin has been shown to prevent outbreaks of Mycoplasma pneumonia and to decrease the occurrence of respiratory infections. Another preventive measure is minimizing the transfer of respiratory droplets from infected persons to others.

Bibliography

Brooks, Geo F., et al. “ Mycoplasma and Cell Wall Defective Bacteria.” In Jawetz, Melnick, and Adelberg’s Medical Microbiology. 25th ed. New York: McGraw-Hill Medical, 2010.

Mandell, Lionel A., et al. “Infectious Diseases Society of America/American Thoracic Society Consensus Guidelines on the Management of Community Acquired Pneumonia in Adults.” Clinical Infectious Diseases 44 (2007): S27-S72.

Ryan, Kenneth J. “ Mycoplasma and Ureaplasma.” In Sherris Medical Microbiology, edited by Kenneth J. Ryan and C. George Ray. 5th ed. New York: McGraw-Hill, 2010.