Legionairre’s Disease is caused by the bacillus Legionella pneumophila. This organism is technically Gram-negative, but it doesn’t take up the staining really well so if you’re trying to visualize it, you’ll have to use silver staining.
It has a single flagellum that helps it move through the environmental fresh water sources where it normally lives. Occasionally, this organism will contaminate the water in air conditioning units, and be blown throughout a hotel, hospital, nursing facility, whatever. The people within that building will then inhale those contaminated aerosols and the bacterium will infect their respiratory tract. This bacteria loves to replicate within the alveolar macrophages and hides within a vacuole there.
This infection can just be a mild, flu-like illness called Pontiac Fever, or it can cause a pneumonia called Legionnaires Disease. This will present as a pneumonia that is accompanied by confusion, and a watery diarrhea, which is really unique for a pneumonia illness.
Occasionally, the kidney’s can be damaged causing hyponatremia, leading to the patient having: nausea, vomiting, headache, seizures, and coma.
The juxtaglomerular apparatus can also be destroyed in the kidneys which reduces the kidney’s ability to secrete renin, causing the development of a Type-IV (hyperkalemic) renal tubular acidosis, leading to the patient having: polyuria, polydypsia, seizures, and respiratory failure.
The more preferred method of diagnosis for an infection of Legionella pneumophila, is urine antigen testing. Urine antigen testing uses antibodies against the lipopolysaccharide antigens from L. pneumophila. It is relatively sensitive, very specific, and ready within hours. You can culture sputum samples, but this organism will only grow on Buffered Charcoal Yeast Extract (BCYE) which has cysteine and iron. Cultures take days to develop, which is why the urine antigen testing is preferred.
The patients who are more susceptible to this infection are people with advanced age, and people with respiratory comorbidities like people who smoke (cigarettes or vaping) or patients with COPD. People who have recently traveled are also at a higher risk of acquiring this infection, especially if those patients stayed in a hotel, or went to a spa or hot tub.
This organism does create beta-lactamase, so treatment with fluoroquinolones is preferred. Fluoroquinolones seem to lower the hospitalization time compared to macrolides.
A 76-year-old male presents to the emergency department with dyspnea for the past 3 days, and watery diarrhea for the past 24 hours. Vital signs reveal a temperature of 102F, a respiratory rate of 30 breaths/min, a pulse of 120 beats/min, and an oxygen saturation of 77% on room air. Lung ascultation revealed crackles in the middle and basal zones of both lungs. Past medical history is significant for a history of smoking. Radiography of the chest revealed dense, multilobular consolidations. What is the fastest method to confirm the suspected diagnosis?
A. Blood cultures
B. Fecal antigen testing
C. Sputum culture
D. Urine antigen testing
First, diagnose the patient.
This patient is presenting with fever, dyspnea, respiratory distress, and lung infiltrates, which is suggestive for pneumonia. The patient is also having watery diarrhea, which is highly suggestive of Legionnaire’s Disease.
A. Legionella pneumonphila doesn’t disseminate into the blood often, so blood cultures are not recommended.
B. Legionella pneumophila does secrete any antigen in fecal matter, so fecal antigen testing is not recommended.
C. Sputum culture on Buffered Charcoal Yeast Extract agar can definitely confirm Legionella pneumophila infection, but growth takes about a week to occur.
D. Urine antigen testing for L. pneumophila infection takes approximately 5 hours, and is relatively sensitive and specific. Therefore it is the fastest method to diagnose patient’s with Legionnaire’s Disease.
Therefore,
An 82-year-old female presents with a productive cough and dyspnea. Vital signs reveal a temperature of 101.3F, a respiratory rate of 24 breaths/min, a pulse of 108 beats/min, and a blood pressure of 120/80 mmHg. Chest radiography reveals bilateral infiltrates in the lower lung zones. Sputum cultures were plated on many agar types including blood agar, chocolate agar, Eaton’s agar, and Lowenstein-Jensen agar, but only produced growth on Buffered Charcoal Yeast Extract agars. What is the most likely diagnosis?
A. Mycoplasma pneumoniae
B. Streptococcus pneumoniae
C. Legionella pneumophila
D. Mycobacterium tuberculosis
First, diagnose the patient.
This patient is presenting with dyspnea, productive cough, fever, tachycardia, and lung infiltrates, which is suggestive of pneumonia.
A. Mycoplasma pneumoniae is a common cause of atypical pneumonia and often causes “walking pneumonia” which is when the patient’s symptoms are less severe than the chest X-ray suggests. This is an acid-fast organism, and requires Eaton’s agar to grow because it requires sterols.
B. Streptococcus pneumoniae is the most common cause of pneumonia, but it would grow on simple agars like a blood agar.
C. Legionella pneumophila can cause pneumonia espeically in elderly patients. This organism is fastidious and will only grow on Buffered Charcoal Yeast Extract agar.
D. Mycobacterium tuberculosis typically causes a chronic, non-productive cough. This will only grow on Lowenstein-Jensen agar.
Therefore,
References:
https://microbewiki.kenyon.edu/index.php/Legionella_pneumophila
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6178616/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2863363/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5576257/
https://journals.viamedica.pl/advances_in_respiratory_medicine/article/view/34795/25401
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