Mycoplasma Pneumonia

Pneumonia caused by Mycoplasma pneumoniae, a cell-wall-deficient bacterium that attaches to respiratory epithelium and injures it through the P1 adhesin and the toxin CARDS. It accounts for about 15 to 20% of community acquired pneumonia in school age children and young adults and a smaller share in adults over 40.

• Epidemics occur every 3 to 7 years. Incubation is about 2 to 4 weeks. Spread is by respiratory droplets in close contact settings (households, schools, military camps). Only about 3 to 10% of infections progress to pneumonia; most cause tracheobronchitis.
• Immune mediated extrapulmonary disease results from cross reacting antibodies and immune complexes. Severe pneumonia, necrotising pneumonia and macrolide resistant disease occur, especially in children.
• Mortality is very low in healthy hosts. Risk factors for severe disease: sickle cell disease, immunoglobulin deficiency, chronic lung disease, Down syndrome, and macrolide resistance.

• Insidious onset over 1 to 3 weeks: malaise, headache, sore throat, low grade fever, and a persistent dry, hacking cough that can last 4 to 6 weeks. Wheeze is common in children and may unmask asthma. Chest signs are few; patients are often well enough to keep working ("walking pneumonia").
• Extrapulmonary features: haemolytic anaemia from cold agglutinins (IgM anti-I), rash (erythema multiforme, Mycoplasma induced rash and mucositis, Stevens-Johnson syndrome), bullous myringitis, arthralgia, hepatitis, pancreatitis, myocarditis, pericarditis, meningoencephalitis, cerebellar ataxia, Guillain-Barre syndrome, transverse myelitis, glomerulonephritis, Raynaud phenomenon.
• Differential diagnosis: viral pneumonia, pneumococcal pneumonia, Chlamydophila and Legionella pneumonia, pertussis, tuberculosis, asthma, hypersensitivity pneumonitis, eosinophilic pneumonia.
• Complications: pleural effusion (about 20%), necrotising pneumonia, pneumatocele, ARDS, acute chest syndrome in sickle cell disease, bronchiolitis obliterans, post-infectious asthma, haemolysis, and neurological sequelae.

• Chest X-ray: reticulonodular or patchy infiltrate, often unilateral and lower zone, sometimes lobar; effusion; findings are worse than the signs.
• Blood tests: full blood count (normal white count, anaemia and reticulocytosis if haemolysis), CRP, liver function, direct antiglobulin test, cold agglutinin titre (1:64 or more supports the diagnosis but is non-specific).
• Mycoplasma PCR on nasopharyngeal or throat swab, or sputum, is the preferred test; serology (IgM, or a four fold rise in IgG) is slower. Where available, test for macrolide resistance mutations (23S ribosomal RNA A2063G).
• Exclude tuberculosis and HIV when appropriate. CT for suspected necrotising pneumonia.

• Mild disease is self-limited and may need only symptomatic care; treat moderate to severe disease, admitted patients, and patients with risk factors.
• Adults:
  • Azithromycin 500 mg on day 1 then 250 mg daily for 4 days (or 500 mg daily for 3 days).
  • Clarithromycin 500 mg twice daily for 7 to 14 days, or erythromycin 500 mg four times daily for 10 to 14 days.
  • Doxycycline 200 mg on day 1 then 100 mg twice daily for 7 to 14 days.
  • Levofloxacin 750 mg daily for 5 to 7 days, or moxifloxacin 400 mg daily, for macrolide failure or intolerance.
• Children:
  • Azithromycin 10 mg/kg once on day 1 then 5 mg/kg daily on days 2 to 5 (maximum 500 mg then 250 mg).
  • Clarithromycin 15 mg/kg/day in 2 divided doses for 7 to 14 days.
  • Doxycycline 2.2 mg/kg twice daily (maximum 100 mg) for 5 to 10 days when macrolide resistance is likely (short courses cause little tooth staining); levofloxacin 10 mg/kg twice daily (age under 5) or 10 mg/kg daily (age 5 or older) only when no alternative exists.
• Macrolide resistant disease (resistance exceeds 30 to 50% in parts of East Asia and varies in other regions; data from Africa are limited): suspect it when fever persists beyond 48 to 72 hours of macrolide therapy, then switch to doxycycline or a fluoroquinolone.
• Corticosteroids for refractory or severe disease with persistent fever, large effusion, necrotising pneumonia or extrapulmonary disease: prednisolone 1 to 2 mg/kg/day for 3 to 7 days, or methylprednisolone 1 to 2 mg/kg/day IV for 3 days (evidence is limited).
• Complications:
  • Cold agglutinin haemolysis: treat the infection, keep the patient warm, transfuse warmed blood if needed, and give prednisolone 1 mg/kg/day for severe haemolysis (evidence is limited).
  • Effusion: place a chest drain if the effusion is large or empyema develops, with intrapleural alteplase 10 mg plus dornase alfa 5 mg twice daily for 3 days when loculated.
  • Stevens-Johnson syndrome: stop non-essential drugs and give supportive care in a burns or intensive care unit.
  • Post-infectious cough and wheeze: inhaled salbutamol 100 to 200 micrograms as needed.
• Supportive care: oxygen for SpO2 less than 92%, paracetamol 1 g four times daily (15 mg/kg per dose in children), fluids, rest. Cough suppressants have limited use.
• Special groups:
  • Sickle cell disease (acute chest syndrome): oxygen, incentive spirometry, azithromycin plus a cephalosporin (ceftriaxone 2 g daily), analgesia, and transfusion or exchange for severe disease.
  • Pregnancy: azithromycin or erythromycin; avoid doxycycline and fluoroquinolones.
  • Immunoglobulin deficiency: prolonged therapy and immunoglobulin replacement under specialist care.
  • Renal impairment: adjust levofloxacin; azithromycin needs no adjustment unless severe.
• Prevention: hand and respiratory hygiene; avoid close contact during illness; there is no vaccine. Antibiotic prophylaxis for contacts is not given routinely, except in outbreaks in closed settings under public health advice.
• Red flags: hypoxaemia, respiratory distress, large effusion, haemolysis with jaundice, neurological signs, rash with mucosal ulceration, no response at 72 hours.
• Follow up: review at 48 to 72 hours and at 2 to 6 weeks; chest X-ray resolves in 4 to 6 weeks (longer in children); investigate persistent cough beyond 8 weeks for asthma, pertussis or tuberculosis.