Melioidosis

Melioidosis, also known as Whitmore disease, is an infectious disease caused by the bacterium Burkholderia pseudomallei. It is predominantly seen in tropical climates in Southeast Asia and Northern Australia, where it is transmitted via contact with contaminated water or soil. The clinical course of Melioidosis can vary greatly, ranging from asymptomatic disease to acute or chronic infection. In some cases, there is a latency period after initial infection, followed by reactivation. Symptomatic disease manifests with localized symptoms, pulmonary symptoms, or disseminated systemic symptoms. Antimicrobial therapy is the mainstay of treatment; in severe cases, adjunct therapy is also required. There are no vaccinations available against B. pseudomallei; prevention involves avoiding potentially contaminated sources, wearing protective gear in environments where there is a risk of contracting the pathogen, and observing general contact measures when interacting with infected patients (e.g., gloves, gowns).

• Distribution: occurs in tropical climates, mainly in Southeast Asia (e.g., Thailand, Malaysia) and Northern Australia
• Incidence: ∼ 150,000 case/year worldwide, with most cases occurring in wet seasons

References:^[1]

Epidemiological data refers to the US, unless otherwise specified.

• Pathogen: Burkholderia pseudomallei
  • Facultative intracellular gram-negative bacterium
• Transmission
  • Percutaneous inoculation: contact with contaminated soil or water (most common)
  • Inhalation, aspiration, or ingestion of contaminated dust or water
  • Person-to-person transmission is rare

• Risk factors
  • Diabetes mellitus
  • Chronic renal, liver, or lung disease (e.g., cystic fibrosis)
  • Immunocompromised states (e.g., malignancy, long-term glucocorticoid use)
  • Occupational exposure: agricultural work

References:^[1][2]

• Incubation period: 1–21 days (mean ∼ 9 days)
• Most cases are subclinical or asymptomatic.
• Symptomatic cases can be acute, chronic (> 2 months), or reactivations of latent infection.
• Clinical features depend on the infected organ:
  • Acute pulmonary infection (most common): wide range of presentations (mild to severe)
  • Localized infection: skin ulcer, nodule, or abscess
  • Visceral abscesses: especially in the prostate, spleen, kidney, and liver
  • Disseminated infection: occurs in ∼ 55% of cases and has a 20% mortality rate. Manifests with fever and septic shock.

References:^[1][3]

• Laboratory testing
  • Culture: mainstay of diagnosis
  • Gram stain of sputum or abscess pus
• Imaging
  • Chest radiography: may show signs of acute pneumonia
  • CT and MRI imaging: to identify abscess formation in multiple organs

References:^[1]

• Community-acquired pneumonia
• Pulmonary tuberculosis
• Fever of unknown origin
• Nocardiosis
• Anthrax
• Sepsis
• Enteric fever
• Malaria

References:^[1]

The differential diagnoses listed here are not exhaustive.

• Antimicrobial therapy
  • Initial intensive therapy: IV ceftazidime, imipenem, or meropenem for 10–14 days
  • Followed by eradication therapy: oral TMP/SMX (plus doxycycline) for 3–6 months
• Adjunct therapy: abscess drainage

References:^[4][5]

• In endemic areas, contact with soil and standing water should be avoided (e.g., agricultural workers should wear boots).
• Health care and laboratory workers should wear masks, gloves, and gowns to prevent infection.
• No vaccination available

References:^[6]