Coccidioidomycosis

Description

• A pulmonary fungal infection caused by the dimorphic fungus, Coccidioides immitis, which is endemic to the southwestern deserts of the United States:
  • Transmitted through inhalation of air-borne fungal spores (arthroconidia)
  • Rarely progresses to involve extrapulmonary sites (<1%): bone, CNS, endocrine/metabolic, musculoskeletal, nervous, pulmonary, skin, and exocrine systems
  • Incubation period is 1 to 4 weeks after exposure.
  • Pulmonary infection most common clinical manifestation; most commonly subacute; more than half of infections are subclinical (1).
• Synonym(s): desert rheumatism; cocci; valley fever

Epidemiology

Affects patients of all ages, with no gender predilection

Incidence

• In the United States: 150,000 cases estimated per year (0.5% extrapulmonary); only about 10,000 cases are actually reported. Overall incidence is rising; 73% increase in African Americans, who also have a higher rate of invasive disease than Caucasians (2)
• Endemic in
  • Southern Arizona
  • Southern and Central California
  • Southwestern New Mexico, West Texas
  • Parts of Mexico, Central and South America
• Increased construction activities, such as home-building, especially in the southwestern United States, has likely resulted in increased aerosolization of fungal spores from soil, leading to increased exposure to and infection with C. immitis.
• From 1940 to 2015, 47 worldwide outbreaks were reported (1,500 cases total) (3). Outbreaks occurred after an earthquake, a large dust storm, construction, archaeological sites, military maneuvers, and laboratory exposures (3).

Prevalence
Up to 17–29% of community-acquired pneumonias in endemic areas (1)

Etiology and Pathophysiology

• C. immitis is a soil-dwelling fungus well adapted to arid conditions. The organism can remain dormant in the soil for years.
• Liberated spores (arthroconidia) are inhaled when soil is disturbed. Upon inhalation, spores convert to spherules in the lung to cause clinical disease.
• Infrequently, spores are introduced through a wound.

Risk Factors

• Certain groups are more prone to dissemination:
  • Immunosuppressed patients: chemotherapy and/or immunosuppressive drugs for cancer or transplant patients, diabetes mellitus, HIV/AIDS, long-term steroid use, transplant patients, pregnancy
  • Blacks and Filipinos at higher risk
• Previously infected patients can experience relapse years later through cell-mediated immune deficiency.
• CNS involvement more common in young white men

General Prevention

• No person-to-person spread
• Lab cultures are highly contagious (inhalation); use caution when handling specimens.
• High-risk patients should avoid archaeological digs, spelunking, or exposure to dust in endemic areas (difficult due to construction, dust storms, etc.).