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Key Features

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Essentials of Diagnosis
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  • Residence in or travel to an endemic area

  • Pneumonia with flulike illness

  • If disseminated, hepatosplenomegaly, anemia, leukopenia

  • Histoplasmal antigen in urine, blood, bronchoalveolar lavage fluid or CSF

  • Detection by staining the organism in smears or tissue, or by culture

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General Considerations
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  • Histoplasma capsulatum is found in the central and eastern United States (Ohio and Mississippi River valleys), Mexico, and most of South America

  • Soil contamination is enhanced by the presence of bat or bird feces

  • Infections in endemic areas are very common at all ages and are usually asymptomatic

  • Over two-thirds of children are infected in these areas

  • Human-to-human transmission does not occur

  • Congenital infection does not occur

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Clinical Findings

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Symptoms and Signs
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  • Asymptomatic in 90% of infections

  • Pneumonia

    • Approximately 5% of patients have mild to moderate disease

    • Cause of this illness is usually not recognized as being Histoplasma

    • Acute pulmonary disease may resemble influenza with fever, malaise, myalgia, arthralgia, and cough occurring 1–3 weeks after a heavy exposure (may be longer with less intense exposure)

    • Subacute form resembles infections such as tuberculosis with cough, weight loss, night sweats, and pleurisy

    • Chronic disease is unusual in children

    • Physical examination may be normal or rales may be heard

    • A small number of patients may have immune-mediated signs such as arthritis, pericarditis, and erythema nodosum

  • Disseminated infection (5% of infections)

    • Fungemia during primary infection probably occurs in the first 2 weeks of all infections, including those with minimal symptoms

    • Transient hepatosplenomegaly may occur, but resolution is the rule in immunocompetent individuals

    • Heavy exposure, severe underlying pulmonary disease, and immunocompromise are risk factors for progressive infection characterized by

      • Anemia

      • Fever

      • Weight loss

      • Organomegaly

      • Bone marrow involvement

      • Death

    • Dissemination may occur in otherwise immunocompetent children; usually they are younger than age 2 years

  • Other forms

    • Ocular involvement consists of multifocal choroiditis

    • Usually occurs in immunocompetent adults who exhibit other evidence of disseminated disease

    • Brain, pericardium, intestine, and skin (oral ulcers and nodules) are other sites that can be involved

    • Adrenal gland involvement is common with systemic disease

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Differential Diagnosis
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  • Pulmonary disease resembles

    • Viral infection

    • Other causes of community-acquired pneumonia

    • Tuberculosis

    • Coccidioidomycosis

    • Blastomycosis

  • Systemic disease resembles

    • Disseminated fungal or mycobacterial infection

    • Leukemia

    • Histiocytosis

    • Cancer

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Diagnosis

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Laboratory Findings
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  • A positive skin test or serology can detect asymptomatic histoplasmosis

  • Routine tests are normal or nonspecific in the benign forms

  • Pancytopenia is present in many patients with disseminated disease

  • Organisms can be seen on histology or culture

  • Tissue yeast forms

    • Small and may be mistaken for artifact

    • Usually found in macrophages, occasionally in peripheral blood leukocytes in severe disease

    • Infrequently found in sputum, urine, or CSF

  • Cultures of infected fluids or tissues may yield the organism after 1–4 weeks of incubation on fungal media, but even ...

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