Rhodococcus hoagii

Background

Microbiology

• Facultative intracellular, non-spore-forming, Gram-positive, weakly acid-fast coccobacillus
  • More coccoid when grown on solid media, and more bacillary with varying lengths (often beaded) when grown in liquid media
• Within the family Nocardiaceae and order Actinomycetes
• Obligate aerobic and facultatively intracellular
• Found in dry and dusty soil
• Makes red pigment, hence the name

Epidemiology

• Infects domesticated animals: Horses (and in foals it causes pneumonia), Goats, Pigs, Sheep, and Cattle
• Most commonly infects people with cell-mediated immunodeficiency, particularly HIV, with or without a notable infectious exposure

Risk Factors

• HIV accounts for 65% of cases
• Solid organ and hematopoietic stem cell transplantation
• Diabetes
• Alcohol abuse
• Chronic renal failure
• Leukemia, lymphoma, lung cancer
• Sarcoidosis
• Preterm infants

Clinical Manifestations

• Necrotizing pneumonia is usual presentation, as well as nodules, cavitation, pleural effusion, and lung abscess
  • Typically subacute onset with fever, cough, and fatigue, as well as pleuritic chest pain
• Specifically in immunocompromised patients, it can cause a cavitary lung disease and is on the differential with mycobacteria and nocardiosis
• Extrapulmonary disease can occur with or without pulmonary involvement
  • In conjunction with other infections, can have abscesses in liver, spleen, thyroid, kidney, psoas, bone, prostate, intraabdominal cavity, and paraspinous tissue
• Extrapulmonary disease without pulmonary involvement has three main presentations:
  • Localized infection following traumatic inoculation, causing wound infection, traumatic septic arthritis, or endophthalmitis
  • Isolated bacteremia with fever, typically recently after chemotherapy causing neutropenia
  • Gastrointestional inoculation followed by lymphatic dissemination, causing peritonitis, pelvic masses, and mesenteric adenitis
  • Others include otitis media with mastoiditis, colonic polyp infection, and osteomyelitis

Diagnosis

• May be misidentified as Corynebacterium in blood culture or Kocuria on Vitek

Management

• Recommend using at least two agents given increasing rates of resistance
  • First-line: combination of macrolide or fluoroquinolone plus rifampin
  • First-line: combination of macrolide or fluoroquinolone plus two of: vancomycin, imipenem, linezolid, or an aminoglycoside
  • Doses are:
    • Azithromycin 500 mg PO/IV once followed by 250 mg PO/IV daily
    • Fluoroquinolones: moxifloxacin 400 mg PO daily (preferred), levofloxacin 500 mg PO daily, or ciprofloxacin 750 mg PO BID
    • Rifampin 600 mg PO once daily
  • Increasing resistance to doxycycline, rifampin, and TMP-SMX
• Treatment usually 6 months or longer