The scenario describes a cluster of five out of 35 residents in a long-term care facility developing high fever, nasal discharge, and a dry cough, suggesting a potential respiratory infection outbreak. The Certification Board of Infection Control and Epidemiology (CBIC) emphasizes the "Identification of Infectious Disease Processes" and "Surveillance and Epidemiologic Investigation" domains, which require selecting the most appropriate diagnostic tool to identify the causative agent promptly. The Centers for Disease Control and Prevention (CDC) provides guidance on diagnostic approaches for respiratory infections, particularly in congregate settings like long-term care facilities.
Option C, "Nasopharyngeal swab," is the best diagnostic tool in this context. The symptoms—high fever, nasal discharge, and a dry cough—are characteristic of upper respiratory infections, such as influenza, respiratory syncytial virus (RSV), or other viral pathogens common in congregate settings. A nasopharyngeal swab is the gold standard for detecting these agents, as it collects samples from the nasopharynx, where many respiratory viruses replicate. The CDC recommends nasopharyngeal swabs for molecular testing (e.g., PCR) to identify viruses like influenza, RSV, or SARS-CoV-2, especially during outbreak investigations in healthcare facilities. The dry cough and nasal discharge align with upper respiratory involvement, making this sample type more targeted than alternatives. Given the potential for rapid spread among vulnerable residents, early identification via nasopharyngeal swab is critical to guide infection control measures.
Option A, "Blood culture," is less appropriate as the best initial tool. Blood cultures are used to detect systemic bacterial infections (e.g., bacteremia or sepsis), but the symptoms described are more suggestive of a primary respiratory infection rather than a bloodstream infection. While secondary bacteremia could occur, blood cultures are not the first-line diagnostic for this presentation and are more relevant if systemic signs (e.g., hypotension) worsen. Option B, "Sputum culture," is useful for lower respiratory infections, such as pneumonia, where productive cough and sputum production are prominent. However, the dry cough and nasal discharge indicate an upper respiratory focus, and sputum may be difficult to obtain from elderly residents, reducing its utility here. Option D, "Legionella serology," is specific for diagnosing Legionella pneumophila, which causes Legionnaires’ disease, typically presenting with fever, cough, and sometimes gastrointestinal symptoms, often in association with water sources. While possible, the lack of mention of pneumonia or water exposure, combined with the upper respiratory symptoms, makes Legionella serology less likely as the best initial test. Serology also requires time for antibody development, delaying diagnosis compared to direct sampling.
The CBIC Practice Analysis (2022) and CDC guidelines for outbreak management in long-term care facilities (e.g., "Prevention Strategies for Seasonal Influenza in Healthcare Settings," 2018) prioritize rapid respiratory pathogen identification, with nasopharyngeal swabs being the preferred method for viral detection. Given the symptom profile and outbreak context, Option C is the most effective and immediate diagnostic tool to determine the causative agent.
References:
CBIC Practice Analysis, 2022.
CDC Prevention Strategies for Seasonal Influenza in Healthcare Settings, 2018.
CDC Guidelines for the Prevention and Control of Outbreaks in Long-Term Care Facilities, 2015.
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