Melioidosis (Whitmore Disease)

Definition and Causative Organism

• Dermatology 2-Volume Set 5e, p. 1541

Microbiology Characteristics

• Quick Compendium of Clinical Pathology 5e

Epidemiology

• Endemic regions: Southeast Asia (especially northeastern Thailand, Singapore, Malaysia) and northern Australia (Northern Territory). Cases increasingly reported in Africa, Middle East, Central and South America.
• B. pseudomallei has been identified in the environment along the Gulf Coast of the USA; contaminated imported products (e.g., aromatherapy spray from India) have caused outbreaks in the US.
• Hyperendemic areas: may be the most common cause of severe community-acquired pneumonia (CAP) in northeastern Thailand and northern Australia.
• Seasonality: Over 75% of cases occur during the rainy monsoon season, likely due to aerosolization of bacteria from water and soil.
• Occupational: Rice farmers in Thailand; male-to-female ratio 4:1 (occupational exposure).
• Serologic surveys in rural Thailand show 5-20% of inhabitants have antibodies, suggesting frequent subclinical infection.
• Post-tsunami (December 2004): hundreds of thousands exposed to flood waters; cases of severe post-immersion pneumonic melioidosis were reported across the region.
• Fitzpatrick's Dermatology Vol. 1&2, p. 2874

Routes of Infection

1. Percutaneous inoculation - direct contact of abraded/lacerated skin with contaminated soil or water (most common)
2. Inhalation - of contaminated droplets, soil, or dust
3. Ingestion
4. Sexual intercourse (rare)

Risk Factors for Severe Disease

• Diabetes mellitus (most significant)
• Alcohol use disorder / alcoholic liver disease
• Chronic renal disease
• Chronic lung disease / COPD
• Heart disease, smoking
• Cystic fibrosis (in those who live/travel in endemic areas)
• Near-drowning / tsunami exposure
• Note: HIV infection does NOT significantly increase risk of acquiring disease or severity

Pathogenesis

• Murray & Nadel's Textbook of Respiratory Medicine

Clinical Presentations

1. Acute Melioidosis

• Pneumonic form (most common - ~50% of all cases): abrupt onset fever, chills, cough, dyspnea, chest pain, hemoptysis; can progress to septic shock in 33%.
• Septicemic form: bacteremia - often no identifiable skin source (though many patients have minor foot abrasions); leads to jaundice, hepatosplenomegaly, myocarditis, severe gastroenteritis, miliary pulmonary disease.

2. Chronic/Subacute Melioidosis

• Defined as symptoms present for >2 months.
• Upper lobe cavitary disease resembling tuberculosis (clinically and radiologically).
• Presenting features: fever, weight loss, productive cough, hemoptysis.
• CXR: diffuse miliary nodules that may expand and cavitate; ~50% upper lobe changes, one-third multilobe involvement.
• Draining sinuses, subcutaneous abscesses (especially scalp).

3. Localized/Cutaneous Melioidosis

• ~15-20% of cases have cutaneous manifestations.
• Primary lesion (especially children): ulcer at inoculation site, possibly with purulent exudate.
• Disseminated: multiple superficial pustules, ecthyma gangrenosum, necrotizing fasciitis.
• Chronic: draining sinuses, subcutaneous abscesses (especially scalp).
• Acute suppurative parotitis (usually unilateral) - classic presentation in children from endemic areas.
• Other skin manifestations: cellulitis, granulomatous lesions, purpura, pustules, Sweet syndrome, urticaria.

4. Extrapulmonary Disease

• Genitourinary infection
• Bone/joint: septic arthritis, osteomyelitis
• CNS disease
• Visceral abscesses (liver, spleen, prostate)
• Suppurative lymphadenopathy

Latent Melioidosis

• B. pseudomallei can establish latency and reactivate decades later when the host becomes debilitated. Presentations as unexplained persistent fever years after leaving endemic areas have been reported.

Skin Exposure Risk

Extensive mud exposure illustrating percutaneous inoculation risk - a route of infection in endemic tropical regions.

Diagnosis

Differential Diagnosis

Treatment

Phase 1: Intensive (Induction) Phase

• IV ceftazidime 50 mg/kg up to 2 g three times daily, OR
• IV meropenem 25 mg/kg up to 1 g three times daily (preferred for: ICU-requiring disease, persistent bacteremia, CNS disease)
• Duration: minimum 10-14 days (at least 2 weeks)

Phase 2: Eradication (Maintenance) Phase

• Oral TMP-SMX (co-trimoxazole) - preferred, OR
• Oral amoxicillin-clavulanate
• Duration: ≥3 months (longer for osteomyelitis or multiple suppurative foci)

Key Resistance Profile

• B. pseudomallei is intrinsically resistant to quinolones, macrolides, and aminoglycosides.
• Susceptibility testing must be performed for each isolate.

Prognosis

• Relapse rate: ~10%
• B. pseudomallei can remain latent for decades - recrudescence may occur with any subsequent immune compromise.

Bioterrorism Significance

Summary Table

Sources: Fitzpatrick's Dermatology Vol. 1&2; Dermatology 2-Volume Set 5e; Murray & Nadel's Textbook of Respiratory Medicine; Andrews' Diseases of the Skin; Quick Compendium of Clinical Pathology 5e