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Blastomycosis -- Wisconsin, 1986-1995

Blastomycosis is a disease of humans and animals caused by inhalation of airborne spores from Blastomyces dermatitidis, a dimorphic fungus found in soil. The spectrum of clinical manifestations of blastomycosis includes acute pulmonary disease, subacute and chronic pulmonary disease (most common presentations), and disseminated extrapulmonary disease (cutaneous manifestations are most common, followed by involvement of the bone, the genitourinary tract, and central nervous system) (1). Although the disease is not nationally notifiable, it was designated a reportable condition in Wisconsin in 1984 following two large outbreaks. This report summarizes information about cases of blastomycosis reported in Wisconsin during 1986-1995 and highlights the importance of surveillance for blastomycosis in areas with endemic disease.

In Wisconsin, cases of blastomycosis are reported to the Division of Health (DOH), Wisconsin Department of Health and Social Services. A confirmed case is defined as isolation of B. dermatitidis or visualization of characteristic broad-based budding yeast from a clinical specimen obtained from a person with clinically compatible illness (e.g., subacute pneumonia or characteristic skin lesions).

During 1986-1995, a total of 670 cases of blastomycosis were reported to DOH, representing a statewide mean annual incidence rate of 1.4 cases per 100,000 persons. Of these, 636 (95%) were confirmed. Twenty-five (3.7%) cases were associated with two outbreaks that occurred in 1990 and 1993, with 10 and 15 reported cases, respectively. The median age of all case-patients was 46 years (range: 4 months-95 years); most cases occurred among males (60%) and among adults aged 25-44 years (40%). The mean annual incidence was higher for males than females in all age-groups; the group-specific rate was highest for males aged 45-64 years (2.5 cases per 100,000 population). Of the total reported cases, 29 were fatal (case-fatality rate: 4.3%), and case-fatality rates increased with age (less than or equal to 11 years, 0; 12-24 years, 1.6%; 25-44 years, 1.8%; 45-64 years, 3.4%; and greater than or equal to 65 years, 12.5%). The number of reported cases was similar by month.

Supplemental clinical data were obtained for 378 (72%) of the 522 case-patients with onset during 1989-1995: a total of 287 (76%) had primary pulmonary disease without extrapulmonary manifestations, 68 (18%) had extrapulmonary infection without recognized pulmonary manifestations, and 23 (6%) had both pulmonary and extrapulmonary manifestations. Manifestations among persons with pulmonary disease included fever, cough, weight loss, night sweats, and pleuritic pain. The most frequently involved extrapulmonary sites were the skin, spleen, and genitourinary systems. Supplemental clinical data were available for 27 of the 29 decedents; all primarily presented with acute or chronic pulmonary disease.

A total of 294 (44%) cases occurred in residents of 10 counties in the northern half of the state (mean annual incidence: 5.1-41.9 per 100,000). Four of these counties (all north-central) accounted for 28% of all cases statewide (mean annual incidence: 10.4-41.9 per 100,000). Adapted from: Wisconsin Epidemiology Bulletin 1995;16(no. 2). Bur of Public Health, Div of Health, Wisconsin Dept of Health and Social Svcs.

Reported by: ME Proctor, PhD, JP Davis, MD, State Epidemiologist for Communicable Diseases, Bur of Public Health, Div of Health, Wisconsin Dept of Health and Social Svcs. Childhood and Respiratory Diseases Br, Div of Bacterial and Mycotic Diseases, National Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: In the United States, most reported cases of blastomycosis have occurred in the Ohio and Mississippi river valleys and in the southeastern states (2). Although a review of death records for 1992 indicated blastomycosis was the reported underlying cause of death for 44 persons in the United States (3), epidemiologic patterns for this disease have not been fully characterized because blastomycosis is not nationally notifiable.

Blastomycosis should be considered in the differential diagnosis of subacute lobar or segmental pneumonia, especially in residents of or visitors to areas with endemic blastomycosis. This disease should be considered especially in patients with histories of outdoor recreational activities and with manifestations of pneumonitis refractory to initial antibiotic treatment. Diagnosis of blastomycosis may be based on isolation of B. dermatitidis from specimens obtained from sputum, skin, or tissue biopsy (cultures should be held for at least 4 weeks), or the demonstration of characteristic broad-based budding yeast cells by direct microscopic examination of wet unstained clinical specimens, cytology preparations, or histopathology slides (4). B. dermatitidis colonies can be identified early using recently developed DNA probes (5) and exoantigen technology. There is no skin test for blastomycosis, and available serologic tests (complement fixation and immunodiffusion) lack adequate sensitivity (6). WI-1 antigen, a recently described yeast cell-wall protein, has been used in a radioimmunoassay to diagnose blastomycosis in an area with endemic disease (7); with further development, this test may be useful to diagnose blastomycosis. The treatment of choice is ketoconazole or itraconazole for mild or moderate disease and amphotericin B for patients with central nervous system involvement, patients who are severely immunocompromised, or patients who do not respond to azole therapy (1).

Although the epidemiologic characterization of blastomycosis is based primarily on findings of outbreak investigations, most reported cases are sporadic. Analysis of information regarding sporadic case reports suggests the risk for disease may be greater among middle-aged (i.e., 35-55 years) men who have had outdoor exposures during work or recreation (e.g., forestry workers or hunters) (1,2). Exposure to soil has been the most commonly identified factor associated with risk for infection during outbreaks. Because the incubation period can range from 3 weeks to 3 months, month of onset does not consistently indicate month of exposure or initial infection. Understanding of the ecologic niche of B. dermatitidis is based on the infrequent isolation of the fungus during outbreaks (8,9), which suggests that geographic (e.g., proximity to waterways) and physical factors (e.g., acid pH and high organic content) are conducive to growth of the fungus. These geographic and physical factors characterize northern Wisconsin and may account for the increased incidence in that region.

Development of both sensitive and specific serologic tests for diagnosing blastomycosis will assist in more accurate estimations of disease prevalence and incidence. Similarly, improving methods to detect B. dermatitidis in nature will increase understanding of the ecology and epidemiology of blastomycosis and may assist in developing better prevention measures.

References

  1. Chapman SW. Blastomycosis. In: Mandell GL, Bennett JE, Dolin R, eds. Principles and practice of infectious diseases. 4th ed. New York: Churchill Livingstone, 1995:2353-65.

  2. DiSalvo AF. The epidemiology of blastomycosis. In: Al-Doory Y, DiSalvo AF, eds. Blastomycosis. New York: Plenum Publishing Corporation, 1992: 83-90.

  3. NCHS. Public-use data tape documentation: multiple cause of death for ICD-9 1992 data {Machine-readable data file and documentation}. Hyattsville, Maryand: US Department of Health and Human Services, Public Health Service, CDC, 1994.

  4. Kwon-Chung KJ, Bennett JE. Blastomycosis. In: Kwon-Chung KJ, Bennett JE, eds. Medical mycology. Philadelphia: Lea and Febiger, 1992:248-79.

  5. Stockman L, Clark KA, Hunt JM, Roberts GD. Evaluation of commercially available acridinium ester-labeled chemiluminescent DNA probes for culture identification of Blastomyces dermatitidis, Coccidioides immitis, Cryptococcus neoformans, and Histoplasma capsulatum. J Clin Microbiol 1993;31:845-50.

  6. Kaufman L. Immunodiagnosis of blastomycosis. In: Al-Doory Y, DiSalvo AF, eds. Blastomycosis. New York: Plenum Publishing Corporation, 1992:123-31.

  7. Soufleris AJ, Klein BS, Courtney BT, Proctor ME, Jones JM. Utility of anti-WI-1 serological testing in the diagnosis of blastomycosis in Wisconsin residents. Clin Infect Dis 1994;19:87-92.

  8. Klein BS, Vergeront JM, Weeks RJ, et al. Isolation of B. dermatitidis in soil associated with a large outbreak of blastomycosis in Wisconsin. N Engl J Med 1986;314:529-34.

  9. Klein BS, Vergeront JM, DiSalvo AF, Kaufman L, Davis JP. Two outbreaks of blastomycosis along rivers in Wisconsin: isolation of Blastomyces dermatitidis from riverbank soil and evidence of its transmission along waterways. Am Rev Respir Dis 1987;136:1333-8.




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