Coccidioidomycosis¶
Chapter 219 | Part 5: Infectious Diseases
KEY CLINICAL POINTS¶
- Coccidioidomycosis is caused by dimorphic fungi Coccidioides immitis and C. posadasii, endemic to the Americas, with high prevalence in the southwestern U.S. and northern Mexico.
- Clinical manifestations range from asymptomatic infection (60%) to disseminated disease, with pulmonary nodules, cavities, and meningitis being common presentations.
- Treatment depends on immune status: triazoles (fluconazole/itraconazole) for immunocompetent patients, amphotericin B for severe disseminated disease, and lifelong maintenance therapy for immunosuppressed individuals.
1. DEFINITION & OVERVIEW¶
Coccidioidomycosis (Valley fever) is a fungal infection caused by Coccidioides species. It is a dimorphic fungus that exists as molds in soil and as spherules in host tissues. The disease is endemic to the Americas, with major outbreaks in the southwestern U.S., northern Mexico, and parts of Central/South America.
Table 219-1: Clinical Presentations of Coccidioidomycosis¶
| CLINICAL PRESENTATION | FREQUENCY, % | RECOMMENDED THERAPY |
|---|---|---|
| Asymptomatic infection | 60 | None |
| Primary pneumonia | 40 | In most cases, none |
| Diffuse pneumonia | <1 | Amphotericin B followed by prolonged oral triazole therapy |
| Pulmonary sequelae | 5 | None |
| Disseminated disease | £1 | Prolonged triazole therapy |
| Skin, bone, joint, soft tissue disease | £1 | Prolonged triazole therapy |
| Meningitis | £1 | Lifelong triazole therapy |
1.1 Etiology¶
Coccidioides immitis and C. posadasii are the causative agents. These fungi are indistinguishable clinically but differ in growth rates. C. posadasii grows faster at higher temperatures.
1.2 Life Cycle¶
In the environment, Coccidioides exists as filamentous molds. Inhalation of arthroconidia leads to spherule formation in host tissues. Spherules rupture to release endospores, which can reinfect tissues or revert to mycelial form in soil.
2. EPIDEMIOLOGY¶
Coccidioidomycosis is endemic to the Americas, with high prevalence in the southwestern U.S. (Arizona, California, Nevada, Utah) and northern Mexico. Climate factors like aridity following rainy seasons increase risk. Annual U.S. cases: ~20,000 (Arizona and California account for ~80%).
2.1 Risk Factors¶
Immunosuppression (HIV, organ transplant, corticosteroids), age >50, pregnancy (especially second/third trimester), and occupational exposure to soil.
2.2 Demographics¶
Most cases occur in adults, with higher incidence in males of African/Filipino descent. Dissemination is more common in immunocompromised individuals.
3. ETIOLOGY & PATHOPHYSIOLOGY¶
Coccidioides spreads via airborne arthroconidia. Infection occurs when spores are inhaled, leading to pulmonary infection. Immune status determines disease progression: cellular immunity controls infection, while immunosuppression leads to dissemination.
3.1 Pathogenesis¶
Inhalation of arthroconidia leads to spherule formation in alveoli. Spherules rupture, releasing endospores that can cause local reinfection or disseminate via blood. Dissemination is more likely in immunocompromised hosts.
3.2 Immune Response¶
Cellular immunity (CD4+ T-cells) is critical for controlling infection. Defective immunity leads to granuloma formation, dissemination, and meningitis. Delayed-type hypersensitivity (DTH) is preserved in asymptomatic individuals.
4. CLINICAL FEATURES¶
Most infections are asymptomatic (60%). Symptomatic cases present with fever, cough, pleuritic chest pain, and arthralgias. Disseminated disease involves skin, bones, joints, meninges, and can lead to meningitis or hydrocephalus.
4.1 Pulmonary Manifestations¶
Pulmonary nodules ( ≤ 4 cm), cavities, and fibrosis. Nodules may mimic malignancies on imaging. Cavities may become secondarily infected with bacteria or fungi.
4.2 Disseminated Disease¶
Skin lesions, bone/joint involvement, and meningitis. Coccidioidal meningitis is uniformly fatal without treatment. Hydrocephalus may develop due to CSF obstruction.
5. DIFFERENTIAL DIAGNOSIS¶
Pulmonary coccidioidomycosis must be differentiated from bacterial pneumonia, tuberculosis, and fungal infections (histoplasmosis, aspergillosis). Disseminated disease may mimic sarcoidosis or lymphoma.
6. INVESTIGATIONS & DIAGNOSIS¶
Diagnosis relies on serology (CF, IDCF, EIA), antigen testing (CSF, urine), and imaging. Culture is less sensitive but confirms diagnosis. Molecular assays (PCR) are emerging but not more sensitive than culture.
6.1 Serology¶
Complement-fixing (CF) antibodies are most specific for active disease. IgM and IgG EIA are rapid but may have false positives. CF titer ≥ 1:32 indicates active disease.
6.2 Imaging¶
Chest X-ray shows nodules, cavities, or fibrosis. CT reveals multiple nodules, microsatellites, or pleural effusions. MRI with gadolinium is useful for meningitis.
7. MANAGEMENT & TREATMENT¶
Treatment depends on immune status. Immunocompetent patients with localized disease may not require therapy. Disseminated disease requires antifungals, with triazoles as first-line and amphotericin B for severe cases.
7.1 Antifungal Therapy¶
Triazoles (fluconazole 400 mg/day, itraconazole 200 mg TID) are first-line. Amphotericin B (0.7–1.0 mg/kg/day) is reserved for severe dissemination. Voriconazole/posaconazole are alternatives for refractory cases.
7.2 Maintenance Therapy¶
Lifelong itraconazole is required for immunosuppressed patients (e.g., HIV, organ transplant recipients) with persistent immune suppression.
8. PROGNOSIS & COMPLICATIONS¶
Most cases resolve spontaneously. Disseminated disease has high mortality without treatment. Complications include meningitis, hydrocephalus, and secondary infections. Prolonged symptoms may indicate chronic pulmonary disease.
9. SPECIAL CONSIDERATIONS¶
Pregnancy: Dissemination risk increases in second/third trimester. Triazoles should be avoided in first trimester. Pediatric cases are rare but may present with disseminated disease. Elderly patients have higher dissemination risk due to comorbidities.
10. KEY POINTS & CLINICAL PEARLS¶
- Coccidioidomycosis is endemic to the Americas, with high prevalence in the southwestern U.S. and northern Mexico.
- Most infections are asymptomatic; symptomatic cases present with fever, cough, and arthralgias.
- Serology (CF, EIA) and imaging are key diagnostic tools.
- Triazoles are first-line for immunocompetent patients; amphotericin B for severe dissemination.
- Lifelong maintenance therapy is required for immunosuppressed patients.
- Disseminated disease, especially meningitis, is life-threatening without treatment.