The Diagnostic Laboratory Tests for Histoplasmosis

Abstract

Of 495 patients reported in a large urban histoplasmosis outbreak, we studied 276 whose serologic tests were done in a single laboratory. Serologic test results were positive in 96% of these patients (compared with less than 5% of controls from an endemic area), cultures were positive in 22%, and special stains in 19%. The immunodiffusion test results were negative in 13% of patients who had positive findings by complement fixation, and 1% had positive results only by immunodiffusion. The complement fixation test was almost twice as sensitive as the immunodiffusion test in patients with subclinical infection. The serologic response differed significantly among the clinical syndromes with higher titers in cavitary and lower titers in disseminated disease. Factors associated with titers of 1:64 or greater to both antigens were black race and immunocompetence. High mycelial titers were also associated with more intense exposure, and high yeast titers were associated with age less than 36 years. No prognostic significance could be proved for fourfold titer rises or falls or persistence of precipitins.

Disseminated histoplasmosis in a non-immunocompromised host

“…Apart from histopathogical detection and culture, however, the reliability of these methods is questionable. Due to the long incubation time required for the growth of Hc in culture, histopathological examination remains the only reliable method for timely confirmation of diagnosis in cases of fulminate histoplasmosis [7,10,20,21]. Positive Hc cultures can provide retrospective confirmation of the diagnosis of histoplasmosis.…”

“…In immunologically healthy subjects the infection normally presents as a nonspecific disease limited to the respiratory tract and follows a bland course. Risk factors for dissemination of the fungus include immunosuppressive treatment, advanced age [7,8,11,19], human immunodeficiency virus (HIV) infection [1,5,6,7,20,21], and T-cell defects [13]. Since 1987 extrapulmonary histoplasmosis has been included among AIDS-defining opportunistic infections by the Centers for Disease Control [5].…”

“…The inoculum, HistopIasma capsulatum varietas capsulatum (Hc), occurs in areas with warm, moist, and humid environmental conditions, especially in soil fertilized by bird and bat feces. Infection generally results from inhalation exposure to airborne spores [1,7,10,11,15,17,[19][20][21][22]. As established by means of the histoplasmin skin test reactivity, the degree of infection with the Hc fungus is extremely high (more than 80%) in endemic areas, such as the midwestern and southeastern regions of the United Abbreviations: Hc = Histoplasma capsulatum; AIDS =acquir ed immunodeficiency syndrome; HIV = human immunodeficiency virus Correspondence to: P. Harten…”

Laboratory Diagnostics for Histoplasmosis

“…A titer of 1:8 is positive, indicating previous exposure to H. capsulatum. A titer of Ն1:32 or a 4-fold rise in antibody titer from acute-to convalescent-phase serum is strongly suggestive of active infection (23). Titers usually decrease with disease resolution, but the decline is slow and often incomplete, making antibody clearance impractical as a tool to assess treatment response.…”

“…An EIA method that is more sensitive than CF and ID but with decreased specificity has been described (25). Serology can be useful even in areas that are highly endemic for the disease, where surprisingly, less than 5% of individuals have positive serology on CF or ID (23). The presence of antibodies in the CSF by CF or ID is sufficient to make the diagnosis of Histoplasma meningitis and is more sensitive than the isolation of H. capsulatum on CSF cultures (26).…”