Swimming in still water lakes can expose people to Legionella bacteria, which can cause Legionnaires' disease, a severe form of pneumonia with symptoms including fever, fatigue and difficulty breathing. Clinicians should suspect Legionnaires' disease if a case of pneumonia does not respond to broad-spectrum antibiotics, especially in patients who have recently traveled or who have risk factors such as advanced age, smoking, or chronic disease.

Chest X-ray of a 77-year-old man with Legionnaires' pneumonia showing a combined opacification within the left lower lobe (green arrow), lingula (red arrow), and right upper lobe (blue arrow).

Computed tomography of the lungs shows multiple prominent subcarinal (A), hilar (B), and mediastinal (C) lymph nodes (yellow arrows), as well as areas of consolidation in the left lower lobe (D, green arrow), left superior posterior lobe (red arrow), and right upper lobe (blue arrow) extending into the lingual lobe. Figures A, B, C, and D are consecutive axial images.

Legionnaires' disease is a form of pneumonia caused by Legionella bacteria that can be contracted from naturally standing water, so awareness and early diagnosis are crucial for those at risk.

The authors of a practical article in the Canadian Medical Association Journal (CMAJ) advise open water swimmers to be aware of this risk.

"Legionella infection is a public health hazard because it can be transmitted through contact with natural bodies of water and man-made reservoirs," Dr. Ashley Bryson, an internal medicine resident at the University of Manitoba, and co-authors wrote.

Legionella infection is an atypical cause of community-acquired pneumonia. Known as Legionnaires' disease, it presents with fever, fatigue, respiratory symptoms and sometimes diarrhea. Legionella bacteria thrive in hot and cold water piping systems, air conditioners, public spas, and even warm stagnant water in lakes and rivers. Risk factors for Legionnaires' disease include age over 50, a history of smoking, chronic cardiovascular or kidney disease, diabetes and a compromised immune system.

The 77-year-old patient described in the article went swimming in a natural lake in Iowa two weeks ago. Over the past four days, he had become increasingly frail, accompanied by fever, cough, and repeated sudden falls at home, so he came to the emergency department. Given his travel activity, clinicians suspected Legionnaires' disease because initial standard antibiotic therapy failed to treat his pneumonia.

Less than 100 cases of Legionnaires' disease are reported each year, but cases may be underreported because diagnosis is challenging.

The authors recommend: "Clinicians should consider Legionnaires' disease in patients with pneumonia who do not improve despite broad-spectrum antibiotics, especially if the pneumonia is severe, immunocompromised, or have recent travel history, or when only antimicrobials inactive against atypical pathogens are used."

Compiled from /ScitechDaily

DOI:10.1503/cmaj.241086