Coccidioides immitis

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Coccidioides immitis / (Redirected from Coccidiomycosis)
  • Dimorphic fungus in patients from arid areas in SW US and Mexico, which is mostly asymptomatic but can cause pulmonary disease, and rarely disseminated disease. Also called Joaquin Valley fever.



  • Dimorphic fungus with barrel-shaped arthroconidia in the septated hyphal filamentous form
  • Coccidiomycosis also caused by Coccidioides posadasii outside of California


Distribution of coccidiomycosis
  • Found in thermic soils in arid regions
  • May have an association with small desert mammals, though of unclear significance
  • C. immitis in California, C. posadasii outside of California (southwestern US, Mexico, Central and South America)
  • Incidence in US is increasing over the past few decades, including emergence in Washington state
    • Unlikely to be from increased detection
    • 95% of cases are in California and Arizona
  • Exposures include archaeological sites, desert exposures, dust storms, prisons
    • It is a significant laboratory hazard
  • There is a strain with a mutation that can cause aggressive invasive disease in younger adults


  • Arthroconidia break off of the filamentous form and are inhaled (or inoculated)
  • The then transform into invasive yeast form, characterized by spherules that contain hundreds of endospores
  • The spherules rupture, releasing the endospores and continuing the cycle

Clinical Manifestations

  • Variable, from asymptomatic or mild (60%), to symptomatic (40%), to disseminated and fulminant
  • Incubation period of 1 to 3 weeks
  • Common symptoms:
    • General: fever, arthralgia, myalgia, night sweats
    • Pulmonary: cough, chest pain
    • May be a common cause of community-acquired pneumonia in some endemic regions.
    • Non-specific maculopapular rash (days to weeks after initial fever)
  • May have peripheral eosinophilia
  • Pulmonary infection may present as an acute pneumonia to a chronic pneumonia with fibronodular or fibrocavitary appearance
    • May also have a solitary nodule or a pleural effusion
  • Skin infection can present at site of inoculation, or disseminated
  • Osteomyelitis and native joint septic arthritis, with the vertebral being to the most common site of infection
    • May also cause arthralgias
  • CNS infection with meningitis, presenting as a chronic headache weeks to months after initial infection
    • Onset of meningitis is usually around 5 weeks following onset of respiratory symptoms
    • Typically basilar meningitis but can be other
    • Can cause prostatitis
  • Symptoms may take weeks to many months to resolve

Desert rheumatism


  • Chronic pulmonary disease:
    • Residual lung nodules (~5%)
    • Lung cavity (~5%)
  • Extra-pulmonary dissemination (skin, bones, joints, CNS): ≤1%

Risk factors for disseminated disease

  • Immunosuppression, including HIV/AIDS, pregnancy, TNF-α inhibitors, corticosteroids, and transplantation
  • More common in non-Caucasian populations
  • Age >65 years, diabetes, underlying cardiac or respiratory disease
  • High complement fixation titre >1:16

Differential Diagnosis


  • CT chest[1]
    • Acute disease: lobar and segmental consolidations (75%); multifocal consolidation; nodules; rarely, miliary disease or confluent nodules with cavitation; may have adenopathy or pleural effusions; may have ARDS
    • Chronic changes: residual nodules, chronic cavities, persistent pneumonia with or without adenopathy, pleural effusion, and regressive changes


  • Direct microscopy: typical spherules
  • Culture: fluffy white colonies on routine bacterial or fungal cultures, often within a few days (grows quickly)
  • Serology
    • Immunodiffusion (ID) for IgM and IgG
      • IgM on CSF for coccioidal meningitis
    • Complement fixation for IgG
    • Beta glucan in blood or CSF, but isn't specific
    • Coccidioidal antigen (urine and serum), only useful in disseminated disease
  • For CNS involvement:
    • Check opening pressure, send for fungal culture (25% sensitive), CSF serology (ID or CF, 30-60% sensitive), CSF coccidioidal antigen
    • Glucose normal or low, protein high or normal, predominately lymphocytosis, may have eosinophils
    • Rule out Cryptococcus and TB


  • Many do not need treatment, as infection is asymptomatic or self-limited
    • Not indicated for asymptomatic pulmonary nodules or cavities in immunocompetent people
  • Indications
    • Significant, debilitating illness requiring hospitalization
    • Extensive pulmonary involvement with diabetes, older age, or other comorbidities
    • Chronic cavitary coccidioidal pneumonia
    • Ruptured coccidioidal cavities
    • Extrapulmonary soft tissue infections and bone and joint infections
    • Meningitis
    • High-risk populations: HIV with CD4<250, hematopoietic stem cell transplant, solid organ transplant
    • For immunocompetent, ambulatory patients with acute pulmonary infection, one of
      • Weight loss >10%
      • Night sweats for 3 weeks
      • Infiltrates on more than half of one lung or portions of both
      • Prominent or persistent hilar adenopathy
      • Anticoccidioidal complement fixation antibody titres over 1:16
      • Inability to work
      • Symptoms lasting >2 months
  • Treatment regimens
  • Duration
    • Acute pulmonary disease: 3 to 6 months, or longer
    • Chronic pulmonary infection: 8 to 12 months, or longer
    • Bone and joint disease: amphotericin B induction x 3 months followed by 3+ years of azoles
  • Meningitis
    • High-dose fluconazole until clinical improvement, then lifelong fluconazole 400 mg daily
    • Daily therapeutic LP titrated to opening pressure (like cryptococcal meningitis)

Laboratory Exposure

  • Evacuate lab, seal lab, call Biosafety Officer on call
  • Assess risk to each individual exposed
    • Lower early in culture when it's yeast-like, higher later when it's a well-grown filamentous fungus (usually by 7 to 10 days)
    • Lifting the lid once likely less than breaking the container
    • However, note that in lab exposures, the number of arthroconidia inhaled is often much higher than a natural inoculum, and attack rates are higher than natural exposure
  • For exposed personnel
    • Get baseline serology (if prior exposure, they're at lower risk)
    • Treat with therapeutic-dose itra or fluc 400 mg daily for 6 weeks, as prophylaxis
      • If pregnant, would have to consider prophylactic amphotericin; use of fluconazole may depend on trimester
    • Repeat serology after prophylaxis; if seroconversion, then consider treating for another few months
    • If they become symptomatic during or after prophylaxis, either with fever or respiratory symptoms, they should be further evaluated
      • Serology can lag by 3 to 12 weeks following symptoms
    • Continue to follow for up to 1 year
  1. Jude CM, Nayak NB, Patel MK, Deshmukh M, Batra P. Pulmonary coccidioidomycosis: pictorial review of chest radiographic and CT findings. Radiographics. 2014 Jul-Aug;34(4):912-25. doi: 10.1148/rg.344130134. PMID: 25019431.