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Coccidioidomycosis

Part 5 | Infectious Diseases: Fungal · Part 5 – Infectious Diseases: Fungal · Chapter 219

Key Clinical Points

  1. Coccidioidomycosis is caused by dimorphic fungi C. immitis and C. posadasii, endemic to the Western Hemisphere.
  2. 60% of infections are asymptomatic; 40% develop primary pulmonary disease.
  3. Cellular immunity controls infection; dissemination occurs in ~1% of cases, often with immunosuppression.
  4. Coccidioidal meningitis is uniformly fatal without treatment and requires lifelong triazole therapy.
  5. Diagnosis relies on serology (EIA, IDTP/IDCF), antigen detection, and CF titers (≥1:32 indicates active disease).
  6. Triazoles (fluconazole, itraconazole) are first-line; amphotericin B is reserved for severe cases.
  7. High-dose triazoles may be teratogenic in pregnancy.
  8. Common immunologic manifestations include erythema nodosum and arthralgias ('desert rheumatism').
  9. Coccidioides poses a significant hazard to laboratory personnel if inhaled.
  10. Pulmonary nodules may mimic malignancy on imaging; be wary of false positives in other fungal serologies.

1. DEFINITION & OVERVIEW

• Definition (Harrison's 22e): Coccidioidomycosis, commonly known as Valley fever (see "Epidemiology," below), is caused by dimorphic soil-dwelling fungi of the genus Coccidioides. • Species: Includes C. immitis and C. posadasii; clinically indistinguishable but differ in growth rates at higher temperatures.

1.1 Fungal Biology

• Habitat: Native soils of arid/semi-arid regions (2–20 cm below surface); not found in cultivated soil. • Life Cycle: Endozoan cycle likely involves burrowing rodents. • Morphology: Mycelial phase produces arthroconidia spores (2×5 μm) that become airborne.

2. EPIDEMIOLOGY

• Geography: Endemic between 40°N and 40°S; US states include CA, AZ, NV, NM, UT, TX. • Trends: Increasing cases due to climate change, construction activity, and an aging population. • Projections: Climate models predict expansion of endemicity toward the east and north.

2.1 Risk Factors

• Dissemination Risk Factors: ◦ Male sex, African/Filipino ancestry ◦ Immunosuppression: HIV (CD4 <250/μL), glucocorticoids, solid organ transplants ◦ Biologics: TNF-α antagonists ◦ Pregnancy: Increased risk during second and third trimesters. • Asymptomatic infection is common in immunocompetent individuals.

3. ETIOLOGY & PATHOPHYSIOLOGY

• Dimorphism: Transition between environmental mycelial growth and host-adapted spherule formation.

3.1 Life Cycle

• Environmental Phase: Mycelial growth with arthroconidia spores (2×5 μm). • Host Phase: Inhalation leads to spherule formation in lungs (up to 200 μm). • Replication: Spherules contain endospores; rupture releases new spores → form new spherules. • Reversion: Reverts to mycelium on artificial media or in soil.

3.2 Immune Response

• Asymptomatic/Resolved: Characterized by delayed-type hypersensitivity and T-cell activation. • Disseminated Disease: Characterized by poor granuloma formation and PMN response. • Persistence: Latent spherules in lungs maintain immunity but risk reactivation.

4. CLINICAL FEATURES

• General Presentation: 60% asymptomatic; 40% develop pulmonary symptoms (fever, cough, pleuritic chest pain). • Immune Manifestations: Erythema nodosum (lower extremities), erythema multiforme, Sweet syndrome. • Musculoskeletal: Arthralgias ('desert rheumatism') common in women. • Diagnostic Clues: Rash/arthritis with exposure history, night sweats, eosinophilia, non-response to antibiotics.

4.1 Disseminated Disease

• Incidence: Occurs in ~1% of cases; meningitis is the most fatal form. • Meningitis Presentation: Headache, lethargy, CSF lymphocytosis, hypoglycorrhachia, elevated protein. • Imaging: MRI shows basilar meningeal enhancement; hydrocephalus is common.

4.2 Complications

• Pulmonary Nodules: Typically upper lobes, ≤4 cm; may form thin-walled cavities. • Cavity Risks: Potential for secondary infection or rupture into pleural space. • Chronic Disease: Characterized by scarring and fibrosis, common in patients with pre-existing lung disease.

5. DIFFERENTIAL DIAGNOSIS

• Bacterial Infection: Often misdiagnosed as bacterial pneumonia; distinguished by presence of rash/arthritis. • Malignancy: Pulmonary nodules may mimic malignancy; differentiate via PET enhancement or CT microsatellites. • Other Fungi: Watch for false positives in histoplasmosis or blastomycosis serology. • Secondary Infection: Aspergillus may colonize pulmonary cavities.

6. INVESTIGATIONS & DIAGNOSIS

• Serology: EIA (IgM/IgG) for initial screening; IDTP/IDCF for confirmation. • CF Titer: ≥1:32 indicates active disease or extrathoracic dissemination. • Antigen Detection: Useful in immunocompromised patients. • Culture: 3–7 days on blood agar; lab hazard alert required.

6.1 Diagnostic Algorithm

  1. Serum EIA (IgM/IgG) → 2. IDTP/IDCF confirmation → 3. CF titer assessment → 4. Culture and staining (Papanicolaou, Gomori methenamine silver).

6.2 Laboratory Hazards

• Safety: Coccidioides is a significant lab hazard if inhaled; alert labs to potential diagnosis for containment.

7. MANAGEMENT & TREATMENT

  1. Initial/Severe Treatment: Amphotericin B (0.7–1.0 mg/kg IV deoxycholate or 3–5 mg/kg lipid formulations) for severe dissemination or meningitis.
  2. Long-term Therapy: Triazoles (Fluconazole, Itraconazole) for primary pneumonia, chronic disease, or disseminated cases.
  3. Refractory Cases: Voriconazole or posaconazole as alternatives.
  4. Specialized Therapy: Olorofim for difficult-to-treat meningitis.
  5. Clinical Scenarios: ◦ Asymptomatic/Primary pneumonia: No treatment required. ◦ Disseminated/Meningitis: Lifelong triazole therapy.
  6. Pregnancy: High-dose triazoles may be terutogenic; avoid during pregnancy.

7.2 Drug Therapy Details

• Amphotericin B (Deoxycholate): 0.7–1.0 mg/kg daily or 3x/week (IV). • Amphotericin B (Lipid): 3–5 mg/kg (IV). • Fluconazole: 400 mg/d (minimum); 800 mg for meningitis. • Itraconazole: 200 mg TID (maximum).

7.3 Table 219-1 Summary

• Asymptomatic infection (60%): No treatment. • Diffuse pneumonia (<1% to 5%): Amphotericin B followed by prolonged oral triazole therapy. • Pulmonary sequelae (≤1%): Included in clinical management of pulmonary disease.

8. PROGNOSIS & COMPLICATIONS

• Meningitis: Uniformly fatal without treatment. • Prognostic Indicators: ◦ Rising CF titers (≥1:32) → predicts disease activity/extrathoracic dissemination. ◦ CSF CF antibody presence. ◦ Development of hydrocephalus. • Serology Note: Seropositivity does not equal immunity; resolved cases show declining antibodies.

8.1 Prognostic Indicators

• High CF titers predict disease activity/extrathoracic dissemination. • Resolved cases show declining antibodies; seropositivity eq immunity.

9. SPECIAL CONSIDERATIONS

• Immunocompromised: Higher risk of dissemination (HIV, transplants, TNF inhibitors). • Pregnancy: Increased risk during 2nd/3rd trimesters; triazoles are teratogenic.

10. KEY PEARLS & CLINICAL TRAPS

• Clinical Clues: Rash and arthritis combined with exposure history are highly suggestive. • Laboratory Safety: Coccidioides is a significant hazard; alert labs to potential diagnosis for containment. • Diagnostic Pitfalls: Be aware of cross-reactivity/false positives in histoplasmosis and blastomycosis serology. • Imaging Trap: Pulmonary nodules can mimic malignancy on CT.

Reference Tables

Harrison's 22e, p.1698

CLINICAL
PRESENTATION		 FREQUENCY, % RECOMMENDED THERAPY
Asymptomatic infection 60 None
40
Diffuse pneumonia <1 Amphotericin B followed by
prolonged oral triazole therapy
5
≤1