Several residents of a long-term care facility develop febrile illness within a short period of time. Symptoms include fever, nonproductive cough, myalgia, rigors, dyspnea, and diarrhea. Organisms found in induced sputum samples stain poorly with Gram stain but are visualized easily using silver stain. Urine testing for bacterial antigens is positive in most of the affected individuals. Which of the following is the most likely source of this outbreak?

Question

Several residents of a long-term care facility develop febrile illness within a short period of time.  Symptoms include fever, nonproductive cough, myalgia, rigors, dyspnea, and diarrhea.  Organisms found in induced sputum samples stain poorly with Gram stain but are visualized easily using silver stain.  Urine testing for bacterial antigens is positive in most of the affected individuals.  Which of the following is the most likely source of this outbreak?

Quizplus · Accepted Answer

11ec160b_3894_cde3_9249_1d0fb089397a_MD0001_00 Legionella pneumophila is a thin, pleomorphic, gram-negative rod that stains poorly with Gram stain and does not grow in traditional agar. Detection of the pathogen is typically made with urine antigen testing, but the organism can also be visualized with silver stain and grown on buffered charcoal yeast extract agar supplemented with L-cysteine and iron (ground-glass colonies). L pneumophila has a strong affinity for the lung (hence the name pneumophila) and typically causes a multifocal pneumonia that is preceded by nonspecific symptoms (eg, high fever, myalgia, headache) and diarrhea. L pneumophila is a frequent contaminant of natural bodies of water, municipal water supplies, and water-based cooling systems found in commercial and hospital settings. Aerosolization and subsequent inhalation of contaminated water can lead to outbreaks of Legionella pneumonia. Common nosocomial sources of infection include showers/baths, cooling towers, nasogastric tubes, ventilators, nebulizers, and other respiratory therapy equipment. Cigarette smoking and chronic lung disease increase the risk for infection. (Choice A) Staphylococcus aureus colonizes the anterior nares and can spread from asymptomatic carriers to hospitalized patients or other individuals. Although methicillin-resistant S aureus can cause severe, rapidly progressive pneumonia, the organism appears as gram-positive cocci in clusters. (Choice C) Listeria can be transmitted by contaminated ready-to-eat food. It is associated with febrile diarrhea and is poorly visualized by Gram stain. However, the diagnosis is usually made by visualizing the organism on light microscopy (tumbling motility) or identifying it on blood or cerebrospinal fluid culture. It is not typically identified by sputum sample silver stain or urine antigen testing. (Choice D) Influenza colonizes the nasopharynx, and outbreaks are common in long-term care facilities and other cohabitated settings. Although influenza often causes nonspecific symptoms (eg, myalgia, malaise, fever) and cough, the virus is typically diagnosed by antigen testing from a nasopharyngeal swab. (Choice E) Widespread use of long-term intravascular devices increases the risk of catheter-related bacteremia and sepsis with skin flora such as coagulase-negative staphylococci and S aureus. Bacteremia is typically identified by Gram stain and culture of peripheral blood. Educational objective: Legionella pneumophila commonly contaminates natural bodies of water, municipal water supplies, and water-based cooling systems. The organism is inhaled in aerosolized water and establishes infection via the pulmonary route. Diagnosis is generally made by urine antigen testing, silver stain, or culture on buffered charcoal yeast extract agar supplemented with L-cysteine and iron.

Several Residents of a Long-Term Care Facility Develop Febrile Illness