What is the most likely cause of dyspnea (difficulty breathing) in a patient who handles chickens, with symptoms of Not Being Sick (presumably meaning non-specific or mild symptoms), and should be tested for: a) Histoplasma via Enzyme-Linked Immunosorbent Assay (ELISA), b) Campylobacter, or c) Salmonella?

From the Guidelines

For a chicken handler patient presenting with dyspnea symptoms, the correct diagnostic test would be A. ELISA for Histoplasma. This is because chicken handlers are at risk for developing histoplasmosis, a fungal infection caused by Histoplasma capsulatum, which is found in soil contaminated with bird droppings, particularly from chickens 1. When the patient inhales the fungal spores, they can develop pulmonary histoplasmosis, which commonly presents with respiratory symptoms including dyspnea, cough, chest pain, and fever. The ELISA test for Histoplasma antigen is a sensitive method for detecting active histoplasmosis, particularly in its acute pulmonary form, with a positive likelihood ratio of 43.2, resulting in a posttest probability of 0.98 for an immunocompromised patient with suspected histoplasmosis 1. While chicken handlers can also be exposed to Campylobacter and Salmonella, these bacterial pathogens typically cause gastrointestinal symptoms rather than primary respiratory manifestations. Histoplasmosis is the most likely diagnosis given the occupational exposure and respiratory presentation, making the ELISA for Histoplasma the most appropriate initial diagnostic test for this clinical scenario. Key points to consider in the diagnosis and management of histoplasmosis include:

• The use of ELISA for Histoplasma antigen to gauge the severity of the infection, as its level correlates with severity of illness 1
• The potential for cross-reactivity with other endemic mycoses and limited availability of testing 1
• The importance of monitoring patients' progress while receiving antifungal therapy, as antigen levels decrease with effective therapy and increase with relapse 1. Given the patient's symptoms and occupational exposure, testing for Histoplasma via ELISA is the most appropriate initial diagnostic test, as it is a sensitive and specific method for detecting active histoplasmosis, and can help guide further management and treatment.

From the Research

Causes of Dyspnea

• Dyspnea, or difficulty breathing, can be caused by various factors, including cardiac or pulmonary diseases such as asthma, chronic obstructive pulmonary disease, heart failure, pneumonia, and coronary artery disease 2, 3.
• In patients who handle chickens, histoplasmosis is a potential cause of dyspnea, particularly if they have been exposed to the fungus Histoplasma capsulatum 4, 5, 6.

Diagnostic Testing

• For patients with dyspnea, initial testing should include a complete blood count, basic chemistry panel, electrocardiography, chest radiography, spirometry, and pulse oximetry 2, 3.
• If no cause is identified, second-line noninvasive testing such as echocardiography, cardiac stress tests, pulmonary function tests, and computed tomography scan of the lungs may be suggested 2.
• For patients with suspected histoplasmosis, diagnostic testing may include an assay for Histoplasma antigen in the urine, serology, or culture 4, 5, 6.
• Enzyme-Linked Immunosorbent Assay (ELISA) may be used to test for Histoplasma, but it is not specified as the primary diagnostic test in the provided studies.

Testing Recommendations

• Based on the patient's symptoms and exposure to chickens, testing for Histoplasma via ELISA (option a) is the most relevant test among the provided options 4, 5, 6.
• Testing for Campylobacter (option b) or Salmonella (option c) is not directly related to the patient's symptoms or exposure to chickens, and is not recommended based on the provided studies.