Mycoplasmal pneumonia

1. Mycoplasmal pneumonia Pneumoniacaused by Mycoplasma pneumoniae, often accompanied bypharyngitisandbronchitis

2. Epidemiology • the smallest free-living organisms, facultative anaerobes • no cell wall • accounts for 10 to 20% of all pneumonias and for at least half of all pneumonias in children and young adults • typically community-acquired, spread person to person via droplet nuclei after close and prolonged contact not seen on Gram stain cannot be treated with the β-lactams or vancomycin

3. Clinical findings • most patients are older children, adolescents, and young adults • 75% of patients tracheobronchitis, 5% atypical pneumonia, and 20% asymtomatic • protracted coughing results in tracheal tenderness and a sore chest • the insidious onset is followed by gradual recovery. Upper respiratory symptoms may last for 2 to 3 weeks, and signs of pneumonia may persist for 4 to 6 weeks

4. Sequence of symptoms begins insidiously over days or a week with constitutional symptomatology (e.g. , fever, myalgia, headache, and malaise) then upper respiratory signs and symptoms appear, with combinations of sore throat, cervical adenopathy, hoarseness, earache, coryza, and non-productive cough less commonly, croup or bronchiolitis may supervene, and in a small percentage, pneumonia ensues, at this point, the cough becomes productive

5. Signs: fever, an erythematous pharynx without exudate Laboratory findings: a slight leukocytosis with normal differential count Radiographic findings:manifold. Most patients have unilateral lower lobe segmental abnormalities on the right

6. Diagnosis • Mycoplasma culture • (1) not widely available • (2) recovery of the organism from sputum does not prove the diagnosis because it can persist for a long time after infection ( >4 weeks)

7. Serologic diagnosis:complement fixation test (CFT) or ELISA • 90% of patients either a four-fold rise in antibody titer (2 to 3 weeks apart) or a single titer of 1:32 or greater • Problems:1. CFT titer remain elevated for a year after infection • 2. the glycolipid antigen in CFT not specific for Mycoplasma, also in: human heart muscle, brain , and pancreas, some streptococci and leafy vegetables false-positive • 3. false-negative reactions are seen with both tests • 4. antibody appears only after 7 to 10 days of illness • 5. detection of IgM does not prove current infection butindicate a recent infection (IgM may persist for months)

8. Antigen detection (direct detection): • DNA probes, PCR • Limited in view of prolonged carrier state • The diagnosis is • provedby a four-fold rise in antibody titer • strongly supportedby a single antibody titer of 1:32 or greater, a titer of cold agglutinins of 1:64 or greater, or a single IgM determination

9. Differential diagnosis Psittacosis contact with birds. Q fever exposure to farm animals or cats. Legionella infect older men who smoke. Chlamydia pneumoniae causes a biphasic illness, with sore throat and hoarseness followed by cough. True viruses cause a more fulminant pneumonia Factors suggesting a mycoplasmal etiology sore throat, headache, fever, rash, an indolent course, a paucity of physical findings on examination, and a chest radiograph more abnormal than the physical examination predicted

10. Therapy • Empirical • culture takes time and may be misleading • serologic investigation not diagnostic early in the course • Standard therapy: erythromycin or tetracycline (2g daily in divided doses) • doxycycline, the newer macrolides (azithromycin and clarithromycin) & FQNS can substitute

11. Duration of therapy • most recommendations are for 10 to 14 days of therapy • longer courses of treatment (e.g. 2 to 3 weeks ) may avoid the relapse that occurs in 5 to 10% of patients