Staphylococcal Pneumonia

Lung infection by Staphylococcus aureus, either as an inhaled (primary) pneumonia or as haematogenous seeding from another focus. It causes about 1 to 10% of community acquired pneumonia and about 20 to 30% of hospital acquired pneumonia.

• Forms:
  • Post-influenza necrotising pneumonia, often with Panton-Valentine leucocidin producing strains, in young previously healthy patients, with rapid cavitation and haemoptysis.
  • Hospital acquired or ventilator associated pneumonia, often methicillin resistant.
  • Haematogenous infection: multiple peripheral nodules or cavities from right sided endocarditis, injection drug use, infected lines, osteomyelitis, or septic thrombophlebitis.
  • Infants and children: pneumatocele, empyema and pneumothorax.
• Risk factors: influenza and other viral infection, injection drug use, cystic fibrosis, bronchiectasis, recent hospitalisation, mechanical ventilation, diabetes, end stage kidney disease, HIV, malnutrition, corticosteroids, skin and soft tissue infection.
• Mortality is about 15 to 40% (higher with necrotising pneumonia and ventilator associated methicillin resistant disease).

• Abrupt high fever, rigors, productive cough with purulent or blood streaked (pink frothy) sputum, haemoptysis, pleuritic pain, rapidly progressive dyspnoea, and shock. A recent flu like illness or skin boil is common. Leucopenia in necrotising disease signals toxin mediated injury.
• Haematogenous disease: fever, pleuritic pain, cough, murmur, skin lesions, signs of endocarditis or bone and joint infection.
• Differential diagnosis: pneumococcal and Klebsiella pneumonia, tuberculosis, fungal infection, septic pulmonary emboli, lung abscess, granulomatosis with polyangiitis, pulmonary embolism with infarction, influenza pneumonia.
• Complications: empyema (about 10 to 30%), pneumatocele, pneumothorax, lung abscess, necrotising pneumonia, ARDS, septic shock, toxic shock syndrome, bacteraemia with metastatic infection (endocarditis, osteomyelitis, septic arthritis, meningitis), and bronchopleural fistula.

• Chest X-ray and CT: multilobar consolidation, cavities, pneumatocele, effusion, multiple peripheral nodules with a feeding vessel sign in haematogenous disease.
• Blood cultures (three sets); sputum Gram stain (clusters of Gram positive cocci) and culture with methicillin susceptibility; nasal swab PCR for methicillin resistant Staphylococcus aureus (high negative predictive value); testing for Panton-Valentine leucocidin gene where available; pleural fluid culture.
• Echocardiography (transoesophageal if bacteraemia or lines); MRI of the spine when there is back pain; imaging of other foci.
• Full blood count, CRP, procalcitonin, creatine kinase, creatinine, liver function, lactate, arterial blood gas, influenza PCR, HIV test.

• Admit; manage shock and respiratory failure early.
• Methicillin susceptible Staphylococcus aureus:
  • Flucloxacillin (or cloxacillin) 2 g IV every 4 to 6 hours, or cefazolin 2 g IV every 8 hours.
  • Non-severe penicillin allergy: cefazolin 2 g IV every 8 hours. Severe allergy: vancomycin.
• Methicillin resistant Staphylococcus aureus:
  • Linezolid 600 mg IV or orally every 12 hours (good lung penetration and suppresses toxin production; monitor blood counts weekly beyond 10 to 14 days; avoid with serotonergic drugs because of serotonin syndrome; lactic acidosis and neuropathy with prolonged use), or
  • Vancomycin loading dose 25 to 30 mg/kg IV, then 15 to 20 mg/kg every 8 to 12 hours (trough 15 to 20 mg/L, or area under the curve to minimum inhibitory concentration ratio of 400 to 600), with creatinine monitoring.
  • Ceftaroline 600 mg IV every 12 hours (every 8 hours in severe disease) as an alternative.
• Necrotising pneumonia, Panton-Valentine leucocidin strains and toxic shock (suppress toxin production):
  • Add clindamycin 600 to 900 mg IV every 8 hours (or use linezolid, which has the same effect) to the active beta lactam or vancomycin.
  • Intravenous immunoglobulin 1 to 2 g/kg once may be used in toxic shock (evidence is limited).
• Duration: at least 14 days for pneumonia; 4 to 6 weeks for bacteraemia with metastatic infection, osteomyelitis or endocarditis; empyema and abscess need prolonged therapy plus drainage.
• Source control: remove infected lines; drain empyema (chest drain, with intrapleural alteplase 10 mg plus dornase alfa 5 mg twice daily for 3 days when loculated, or thoracoscopic debridement); drain abscesses; echocardiography and valve surgery assessment in endocarditis.
• Post-influenza disease: add oseltamivir 75 mg orally twice daily for 5 days (up to 10 days in severe disease).
• Supportive care: oxygen, lung protective ventilation (tidal volume 6 mL/kg predicted body weight), vasopressors (noradrenaline 0.05 to 0.5 micrograms/kg/min), venovenous ECMO for refractory hypoxaemia, enoxaparin 40 mg SC daily, nutrition. Massive haemoptysis: tranexamic acid 1 g IV every 8 hours (evidence is limited) and bronchial artery embolisation.
• Decolonisation for recurrent skin and soft tissue infection or recurrent disease: mupirocin 2% nasal ointment twice daily for 5 days plus chlorhexidine 4% body wash daily for 5 days; treat household contacts.
• Special groups:
  • Children: flucloxacillin 50 mg/kg every 6 hours (maximum 2 g), vancomycin 15 mg/kg every 6 hours, clindamycin 10 to 13 mg/kg every 8 hours, linezolid 10 mg/kg every 8 hours (age under 12); early drainage of empyema.
  • Pregnancy: flucloxacillin, cefazolin and vancomycin; linezolid only when necessary.
  • Injection drug use: evaluate for right sided endocarditis, treat addiction (buprenorphine sublingual 2 to 4 mg initially, titrated to 8 to 16 mg daily, or methadone starting at 20 to 30 mg daily with specialist titration), and give a naloxone supply.
  • Renal impairment: adjust vancomycin by trough and avoid with nephrotoxic drugs; linezolid needs no adjustment.
• Red flags: haemoptysis, rapidly progressive cavitation, leucopenia with shock, persistent bacteraemia after 72 hours, new murmur, spinal pain.
• Follow up: repeat blood cultures every 48 hours until negative; echocardiography when bacteraemic; chest X-ray at 6 weeks; review at 2 weeks and after treatment for relapse.