Burkholderia pseudomallei

Background

• Also called melioidosis or Whitmore's disease

Microbiology

• Oxidase-positive, indole-negative Gram-negative bacillus with "safety pin" appearance (i.e. bipolar staining)
• Non-hemolytic
• Colonies start small, smooth, cream-coloured with a metallic sheen, but become dry and wrinkly after 1 to 2 days of incubation
• Inherently resistant to polymixins

Epidemiology

• Humans and animals
• Important cause of death in south-east Asia and northern Australia
  • Up to 80% seroprevalence in Thailand, mostly asymptomatic
  • More cases during the rainy season
  • Sporadic cases elsewhere, including the Middle East, Africa, and the Americas
• May have latent disease with reactivation much later
• Acquired by percutaneous inoculation, inhalation (esp. lab workers), and ingestion
• Risk factors for clinical disease
  • Diabetes
  • Heavy alcohol use
  • Chronic lung disease
  • Chronic kidney disease
  • Treatment with glucocorticoids
  • Cancer
  • Thalassemia

Clinical Manifestations

• Incubation period 9 days (range 1 to 21 days)
• Presentations can vary from asymptomatic, skin ulcers, abscesses, latent infection, chronic pneumonia (similar to TB), or fulminant shock1
  • Pneumonia (50%)
  • Genitourinary infection (15%)
  • Skin infection (15%), with ulcers, nodules, or abscesses
  • Primary bacteremia (10%)
  • Septic arthritis/OM (3-5%)
  • Neuro (3-5%)
  • Disseminated infections can involve liver, spleen, lung, and prostate
• About 50% of clinical cases have bacteremia, and 20% of cases will develop septic shock
• Can occasionally lay latent and reactivate decades after exposure

Diagnosis

• Culture
  • Blood, throat, and urine cultures should be taken from all patients with suspected melioidosis
  • Grows on blood agar, MacConkey, etc. (i.e. not a fastidious organism)
  • Can use selective colistin or polymyxin B
  • On sheep blood agar, grows as small, smooth, cream-coloured colony with metallic sheen
  • May develop a dry and wrinkled appearance after 1 to 2 days of incubation
• MALDI-ToF is not reliable for identifying it
• Other methods
  • PCR
  • Immunofluorescence and latex agglutination
  • Serology (acute/convalescent)

Management

• Intrinsic resistance to many antibiotics, including colistin, primarily using efflux pumps
• Treat with induction followed by eradication therapy
  • Induction: ceftazidime, imipenem, or meropenem for 10-14 days
  • Eradication: TMP-SMX for 3+ months
• Others: amoxicillin-clavulanic acid

Biosafety

• Lab workers can have aerosol exposure
• May need prophylaxis in high-risk patients
  • TMP-SMX or doxycycline or amoxicillin-clavulanic acid
• Monitor with serology at baseline, weeks 1 2 4 and 6 post-exposure
  • Needs to be sent to CDC via NML

Prognosis

• 50% mortality even with high-quality care