Mycoplasma pneumoniae is a very small bacterium which lacks a cell wall. It is sensitive to macrolides, tetracyclines and fluoroquinolones.
It is a common cause of community-acquired pneumonia in children and young adults, but the infection may also produce extrapulmonary symptoms.
The incubation period is 1 to 4 weeks.
Mycoplasma infections usually occur as epidemics at 3- to 5-year intervals.
Clinical presentation
Mycoplasma pneumoniae (Mp) usually causes a mild upper respiratory tract infection that resolves spontaneously (runny nose, cough, sore throat, headache).
Respiratory tract infections caused by Mp usually last for 2 to 3 weeks. Prolonged symptoms lasting for more than one month have been found in approximately 10% of the patients.
Mp may also cause gradually developing pneumonia that may be associated with a prolonged cough.
Mp infection may include extrapulmonary manifestations/symptoms.
Skin and mucous membrane symptoms (exanthema)
Central nervous system symptoms (encephalitis, meningitis, myelitis, polyradiculitis)
Ocular symptoms, gastrointestinal symptoms, hepatitis, muscle and joint symptoms, haematological and cardiac symptoms
Several recurrent infections may occur during a lifetime.
Diagnosis
Mp should be suspected as the cause of a respiratory tract infection if
an epidemic is known to be present
other confirmed cases of Mp infections have occurred in the vicinity
the patient is a child or a young adult.
Chest x-ray is required for diagnosing pneumonia.
Clinical presentation and routine laboratory tests (CRP, white cell count) are not sufficient to allow for differentiation between pneumonia caused by Mp and other bacterial or viral pneumonias.
Laboratory tests
The laboratory diagnosis of an Mp infection is based on specific serological tests and/or a nucleic acid test.
It is advisable to direct diagnostic efforts primarily towards identifying epidemics and particularly during an epidemic towards detecting patients requiring treatment with severe or atypical symptoms.
Antibodies (serology)
A recent infection can be diagnosed by the presence of IgM class antibodies in a serum sample (particularly in children and adolescents; usually positive about a week after symptom onset), or by a significant (at least 2-fold) increase in the amount of IgG class antibodies in paired serum samples taken with an interval of 2-3 weeks.
IgM class antibodies have been described to disappear within approximately one month after the infection. Sometimes IgM antibodies may, however, remain positive for several months or even years. Prolonged detection of IgM class antibodies is not a sign of an active Mp infection.
Even though the diagnosis based on paired samples is only available retrospectively, it is of use when the clinical presentation is atypical (differential diagnosis), in complicated pneumonia and in confirming the presence of an epidemic.
In recurrent infections (often in adults and elderly patients) the IgG concentration is often increased and the IgM response is occasional.
In infections that involve the central nervous system, antibodies may be detected in the cerebrospinal fluid (mycoplasma antibodies are normally not present in the cerebrospinal fluid).
Nucleic acid test
The DNA of Mp can be detected in the sputum, nasopharyngeal aspirate or throat swabs during a respiratory tract infection, but it must be borne in mind that, during an epidemic, the bacteria may also be present in the pharynx of asymptomatic individuals (carrier status) and, moreover, that Mp may persist in the respiratory tract for several months after a healed infection.
A PCR test can provide early diagnosis in the acute phase (already after a few symptomatic days) but there may be variation between laboratories in how quickly the result is delivered (may take up to one week).
The test is also suitable for the detection of extrapulmonary infections (a sample of cerebrospinal or synovial fluid, for example, may be collected), particularly when combined with serology and interpreted with the clinical presentation in mind.
Doxycycline or macrolides are the antimicrobial drugs of choice. Also fluoroquinolones are effective against Mp but they are not recommended as primary drugs.
Macrolide-resistant Mp strains have been described in the 21st century particularly in Asia but also in Europe.
The maximum duration of treatment in Mp pneumonia is 14 days.
Doxycycline 100 mg twice daily (only for patients aged more than 10 years)
A macrolide (e.g. azithromycin for 5 days, first dose 500 mg, then 250 mg once daily; alternatively roxithromycin 150 mg twice daily or clarithromycin 250-500 mg twice daily)
A fluoroquinolone (not as the primary drug; moxifloxacin 400 mg once daily, levofloxacin 500 mg once or twice daily or 750 mg once daily)
Effective pharmacotherapy will shorten the duration of symptoms, even though it does not necessarily eradicate the Mp bacteria from the pharynx.
Antibody assays remain positive for a long time, so it is not worthwhile to use them for assessing treatment response or for follow-up after treatment.
Furthermore, it must particularly be borne in mind that a double infection caused by both Mp and pneumococcus is common, and it is not possible to clinically differentiate between the two infections. Therefore, the treatment of pneumonia should include an antimicrobial drug effective against pneumococci (in outpatient care primarily amoxicillin; see Pneumonia).
No evidence is available of the efficacy of pharmacotherapy in the treatment of other Mp-induced respiratory tract infections. A majority of the infections resolve spontaneously, and the diagnosis is not confirmed until the patient has already recovered. Positive antibody assays alone thus do not warrant initiation of antimicrobial medication.
The treatment of Mp-induced infections involving the central nervous system consists of doxycycline or fluoroquinolones (macrolides do not penetrate the central nervous system easily).
Prognosis
The patient usually recovers well from an Mp infection. In practice, probably a majority of the infections remain undiagnosed and without antimicrobial treatment.
However, after Mp pneumonia the patient may feel weak for a considerably long time, and the cough may persist for several weeks. It may also take a long time before the chest x-ray returns to normal. In rare cases, the pulmonary function may remain impaired for several months.
Top-level athletes are more susceptible than the general population to recurrent respiratory tract infections, and probably also to Mp infections. These infections may be associated with myocarditis. Even athletes must rest when they are febrile and fatigued, and training should be started cautiously and gradually only after an infection with systemic symptoms has subsided.
References
Waites KB, Talkington DF. Mycoplasma pneumoniae and its role as a human patogen. (Review). Clin Microbiol Rev. 2004 Oct;17(4):697-728
Atkinson TP, Balish MF, Waites KB. Epidemiology, clinical manifestations, pathogenesis and laboratory detection of Mycoplasma pneumoniae infections. FEMS Microbiol Rev 2008 Nov;32(6):956-73. [PubMed]