Pulmonary Coccidioidomycosis (Valley Fever)

Pulmonary coccidioidomycosis (Valley Fever, San Joaquin Valley Fever, desert rheumatism, desert fever) is a fungal infection caused by inhalation of arthroconidia (asexual spores) from one of two closely related dimorphic fungal species: Coccidioides immitis (mainly California, San Joaquin Valley) and Coccidioides posadasii (Arizona, southern California, southern Nevada, southern New Mexico, western Texas, Mexico, Central America, parts of South America). The fungi grow as branching hyphae in soil during cool wet seasons, then fragment into arthroconidia (3-5 micrometer barrel-shaped spores) that become airborne in dry windy conditions and are inhaled by humans and animals. In tissues at body temperature, arthroconidia transform into characteristic spherules (30-100 micrometer thick-walled structures filled with endospores), which rupture to release endospores that develop into new spherules — the parasitic phase. The geographic distribution of these fungi defines the endemic regions: 'Coccidioides Belt' includes Arizona (most cases, especially Maricopa and Pima counties), California (San Joaquin Valley and surrounding areas), New Mexico, Texas (especially West Texas), Nevada, Utah, parts of Mexico, Central America, and parts of South America. Cases are increasing in frequency and geographic spread (climate change, drought cycles, construction, dust storms increase soil disturbance). Approximately 150,000-250,000 new infections occur annually in the US, with most cases in Arizona and California. Outbreaks have been associated with archaeological excavations, military training, dust storms, earthquakes, and outdoor occupations.

Clinical presentation: incubation 7-21 days after inhalation. Approximately 60% of infected individuals are asymptomatic (positive serology only); 40% develop symptomatic primary infection. Primary pulmonary coccidioidomycosis: influenza-like illness with fever (sometimes prolonged), fatigue (often profound and prolonged for months), dry cough, pleuritic chest pain, headache, myalgia, arthralgia (especially knees, ankles — 'desert rheumatism'), night sweats, weight loss, and dyspnea. Skin manifestations are characteristic: erythema nodosum (painful, red, raised nodules typically on anterior shins, more common in women, indicates strong immune response and good prognosis) and erythema multiforme (target lesions on extensor surfaces) seen in 5-25% of symptomatic primary infection. Most primary infections resolve spontaneously over weeks to months without antifungal therapy. Pulmonary complications (5-10%): (1) Persistent pneumonia: lasting more than 6-8 weeks, may have areas of consolidation, infiltrates, or pleural effusion. (2) Pulmonary nodules (coccidioidomas): solitary or multiple lung nodules typically 1-3 cm, can mimic lung cancer, often seen at chest imaging follow-up. (3) Cavitary disease: thin-walled cavities (the classic 'grape skin' cavity), usually in upper lobes, may be asymptomatic or cause hemoptysis, pneumothorax, infection. (4) Chronic fibrocavitary coccidioidomycosis: progressive disease in immunocompromised, with multiple cavities, fibrosis, and emphysema. Disseminated extrapulmonary disease (less than 1% of all infections, but more common in high-risk groups): occurs from hematogenous spread, can affect virtually any organ but most commonly skin (verrucous plaques, abscesses, ulcers, sinuses), bones (vertebrae, long bones, hands, feet — osteomyelitis), joints (arthritis), soft tissues, and central nervous system (meningitis — most serious form, requires lifelong therapy). Risk factors for severe and disseminated disease: immunocompromised state (HIV with CD4 less than 250, solid organ transplant, hematopoietic stem cell transplant, biologic therapy especially TNF-alpha inhibitors, high-dose corticosteroids, chemotherapy), pregnancy (especially third trimester and postpartum), race/ethnicity (African American 10-fold and Filipino 175-fold higher risk than Caucasian), diabetes mellitus, age extremes (very young and elderly), male sex (slightly higher risk). Coccidioidal meningitis is the most life-threatening complication: typically presents weeks to months after primary infection with headache, fever, photophobia, neck stiffness, vomiting, mental status changes, and cranial nerve palsies; can cause hydrocephalus, vasculitis, infarcts; CSF shows lymphocytic pleocytosis with elevated protein, low glucose, eosinophilia (15-50% of CSF cells in coccidioidal meningitis — almost pathognomonic).

Diagnosis: maintain high index of suspicion in symptomatic patients with travel or residence in endemic areas. Workup: chest imaging (radiograph or CT showing infiltrates, nodules, cavities, hilar lymphadenopathy, pleural effusion). Serology is the cornerstone: enzyme immunoassay (EIA) for IgG and IgM most commonly used (sensitive but with false positives), confirmed by immunodiffusion (IDCF for IgG, IDTP for IgM, more specific). Complement fixation (CF) titers quantify IgG and have prognostic value (titers 1:16 or higher suggest dissemination, follow titers serially with treatment). Culture from sputum, BAL, tissue is definitive but requires biosafety level 3 laboratory (highly infectious to personnel) — laboratory must be alerted. Histology shows characteristic large spherules (30-100 micrometers) with internal endospores (sometimes mistaken for parasites or other fungi) — can be seen with H&E, GMS, PAS stains. Coccidioides PCR available in some reference labs. Skin testing (spherulin or coccidioidin) historically used for population studies, less useful clinically. CSF analysis for suspected meningitis: opening pressure, cell count with differential (lymphocytic with eosinophilia is highly suggestive), protein, glucose, CSF complement fixation titers (positive in 95%), CSF culture (low yield), CSF beta-D-glucan (elevated in fungal meningitis). Treatment: most primary uncomplicated pulmonary infections in immunocompetent patients resolve spontaneously without antifungal therapy — observation with serology follow-up. Indications for antifungal therapy in primary infection: severe symptoms (high fever, marked weight loss greater than 10%, severe night sweats, prostration), persistent symptoms beyond 4-6 weeks, rising CF titers or complement fixation 1:16 or higher, immunocompromised patient, pregnancy, infants, elderly, diabetes, African American or Filipino ancestry, and pulmonary involvement greater than 50%. First-line therapy: fluconazole 400-800 mg orally daily for 3-6 months (longer if disseminated). Itraconazole 200 mg twice daily is alternative (better for bone disease). Newer azoles (voriconazole, posaconazole, isavuconazole) for refractory cases or intolerance. Amphotericin B (liposomal preferred for nephrotoxicity reduction, 3-5 mg/kg/day IV) for severe pulmonary disease, rapidly progressive disease, dissemination, pregnancy in first trimester (azoles teratogenic). Coccidioidal meningitis: lifelong fluconazole 400-1200 mg/day (relapses common upon discontinuation, mortality high if untreated), with intrathecal amphotericin B for refractory cases; ventricular shunting if hydrocephalus. Surgical resection for cavitary lesions with hemoptysis, mediastinal disease, or fungus ball. Long-term follow-up with serology and imaging. Prognosis: most primary infections excellent recovery; chronic pulmonary disease and dissemination require long-term therapy with relapse risk; coccidioidal meningitis lifelong therapy with mortality if untreated; pregnancy outcomes generally good with appropriate treatment.