Mycobacterium chimaera

Background

Microbiology

• A member of the Mycobacterium avium complex

Epidemiology

• A global outbreak of Mycobacterium chimaera infections was associated with point-source contamination of Stöckert 3T-HCD heater-cooler units (HCUs) used in cardiac bypass
• Higher rates in mainland Europe, followed by UK, followed by North America

Pathophysiology

• The HCUs aerosolized mycobacteria into the surgical field

Clinical Presentation

• Median incubation period was 14.5 months (range 6 weeks to 5 years), with 80% of patients becoming unwell during the first two years
• Duration of symptoms median 7 weeks but up to 1 year
• Most commonly presented with unexplained fever
• Constitutional symptoms are common
• Caused prosthetic valve endocarditis, aortic graft infection, surgical site infections, and disseminated disease affecting liver, spleen, bone marrow, spine, skin, and bone
• Lymphopenia and thrombocytopenia are common, as is elevated ALP

Diagnosis

• Culture in general has sensitivity of 68% but increases to essentially 100% with two cultures
  • Blood, urine, sputum, tissue, et cetera
• Two blood cultures are about 76% sensitive

Management

• No specific guidelines exist for treatment
• Typically use a MAC regimen with azithromycin, ethambutol, and rifampin
• May need additional aminoglycoside such as amikacin for severe disease
• Duration unclear, but at least several months

Prognosis

• Poor prognosis, with median survival of30 months from initial surgery and 9 months from start of therapy

Further Reading

• Mycobacterium chimaera infection following cardiac surgery in the United Kingdom: clinical features and outcome of the first 30 cases. Clin Microbiol Infect. 2018. doi: 10.1016/j.cmi.2018.04.027