| << Chapter < Page | Chapter >> Page > |
Infection by the dimorphic fungus Coccidioides immitis causes coccidioidomycosis . Because the microbe is endemic to the San Joaquin Valley of California, the disease is sometimes referred to as Valley fever. A related species that causes similar infections is found in semi-arid and arid regions of the southwestern United States, Mexico, and Central and South America. DR Hospenthal. “Coccioidomycosis.” Medscape. 2015. http://emedicine.medscape.com/article/215978-overview. Accessed July 7, 2016.
Like histoplasmosis, coccidioidomycosis is acquired by inhaling fungal spores—in this case, arthrospores formed by hyphal fragmentation. Once in the body, the fungus differentiates into spherules that are filled with endospores. Most C. immitis infections are asymptomatic and self-limiting. However, the infection can be very serious for immunocompromised patients. The endospores may be transported in the blood, disseminating the infection and leading to the formation of granulomatous lesions on the face and nose ( [link] ). In severe cases, other major organs can become infected, leading to serious complications such as fatal meningitis .
Coccidioidomycosis can be diagnosed by culturing clinical samples. C. immitis readily grows on laboratory fungal media, such as Sabouraud's dextrose agar , at 35 °C (95 °F). Culturing the fungus, however, is rather dangerous. C. immitis is one of the most infectious fungal pathogens known and is capable of causing laboratory-acquired infections. Indeed, until 2012, this organism was considered a “select agent” of bioterrorism and classified as a BSL-3 microbe . Serological tests for antibody production are more often used for diagnosis. Although mild cases generally do not require intervention, disseminated infections can be treated with intravenous antifungal drugs like amphotericin B .
John’s negative RIDT tests do not rule out influenza, since false-negative results are common, but the Legionella infection still must be treated with antibiotic therapy and is the more serious condition. John's prognosis is good, provided the physician can find an antibiotic therapy to which the infection responds.
While John was undergoing treatment, three of the employees from the home improvement store also reported to the clinic with very similar symptoms. All three were older than 55 years and had Legionella antigen in their urine; L. pneumophila was also isolated from their sputum. A team from the health department was sent to the home improvement store to identify a probable source for these infections. Their investigation revealed that about 3 weeks earlier, the store's air conditioning system, which was located where the employees ate lunch, had been undergoing maintenance. L. pneumophila was isolated from the cooling coils of the air conditioning system and intracellular L. pneumophila was observed in amoebae in samples of condensed water from the cooling coils as well ( [link] ). The amoebae provide protection for the Legionella bacteria and are known to enhance their pathogenicity. HY Lau and NJ Ashbolt. “The Role of Biofilms and Protozoa in Legionella Pathogenesis: Implications for Drinking Water.” Journal of Applied Microbiology 107 no. 2 (2009):368–378.
In the wake of the infections, the store ordered a comprehensive cleaning of the air conditioning system and implemented a regular maintenance program to prevent the growth of biofilms within the cooling tower. They also reviewed practices at their other facilities.
After a month of rest at home, John recovered from his infection enough to return to work, as did the other three employees of the store. However, John experienced lethargy and joint pain for more than a year after his treatment.
Go back to the previous Clinical Focus box .
Notification Switch
Would you like to follow the 'Microbiology' conversation and receive update notifications?
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|