Legionella pneumophila bacteria, 3D illustration, the causative agent of Legionnaire’s disease. (Image by Kateryna Kon on Shutterstock)

WINNIPEG, Manitoba — Summer days spent swimming in lakes are a cherished pastime for many of us. But for one 77-year-old man, a refreshing dip during his Iowa vacation led to an unexpected medical mystery. It would take days before doctors were able to discover his pneumonia was caused by Legionella, the bacteria responsible for Legionnaires’ disease.

Medical professionals at a Winnipeg hospital found themselves dealing with an unusual case when their elderly patient arrived at the emergency department after experiencing multiple falls at home. His symptoms seemed deceptively simple at first—weakness, fever, and a cough producing nonpurulent sputum. Yet this case, published in the Canadian Medical Association Journal, would prove to be anything but routine, ultimately revealing how a common recreational activity exposed him to a dangerous waterborne pathogen.

A freshwater mystery

Before his symptoms began, the man had traveled to Iowa where he stayed in a private home and went swimming in a local lake. Within two weeks of returning home, he started experiencing concerning symptoms that kept getting worse despite having no previous lung problems. His medical history included some chronic conditions—he used a CPAP machine for sleep apnea, took blood thinners for an irregular heartbeat, and had chronic kidney disease, with a baseline creatinine of 150 µmol/L—but nothing that initially pointed to his eventual diagnosis.

When doctors first examined him, his vital signs revealed a blood pressure of 129/68 mm Hg, a heart rate of 100 beats per minute, a respiratory rate of 18 breaths per minute, a temperature of 37.0°C (98.6°F), and an oxygen saturation of 95% while receiving supplemental oxygen through nasal prongs. The medical team heard concerning sounds in his lungs, particularly on the left side, where there were both decreased breath sounds and crackling noises that suggested fluid buildup.

Initial testing revealed several abnormalities—his white blood cell count was elevated, suggesting his body was fighting an infection. He also had high levels of an enzyme called creatine kinase, which can indicate muscle damage, and his kidney function had worsened from its baseline. Chest imaging showed he had developed pneumonia in both lungs, along with lymphadenopathy and areas of consolidation.

Testing for Legionella

The hospital team started him on piperacillin-tazobactam, an antibiotic typically used for severe pneumonia. They also administered single doses of two other antibiotics—vancomycin and azithromycin. However, after five days of treatment, his condition hadn’t improved as expected. This prompted them to perform a bronchoscopy—a procedure where a thin tube with a camera is inserted into the airways to collect fluid samples for testing.

Here’s where the case took an interesting turn. When the medical team tried to order specialized testing for Legionella bacteria, the laboratory initially rejected the request. This wasn’t due to an oversight—rather, it reflected an important system designed to prevent unnecessary testing. The hospital had a system requiring clinical justification before running Legionella tests to prevent overuse.

After the doctors explained their patient’s risk factors—recent travel, exposure to standing water, and pneumonia that wasn’t responding to standard antibiotics—the laboratory agreed to perform the Legionella testing. Their persistence paid off: while one test came back negative, a urine test was positive for Legionella antigen, confirming their suspicion. Although the bronchoalveolar lavage culture was negative, doctors suspected this was due to a recent dose of azithromycin, as well as other factors like mild disease burden or sampling limitations.

Based on these findings, doctors prescribed levofloxacin, a specific antibiotic effective against Legionella, at a dose of 750 mg to be taken orally for 10 days. The patient responded well to this targeted treatment and was able to leave the hospital on the fourth day of this new medication, no longer needing supplemental oxygen.

What is Legionnaires’ disease?

Legionnaires’ disease is more common than many people realize, though it often goes undiagnosed. In Canada, fewer than 100 cases are reported each year, but health experts believe the actual number is much higher. The bacteria responsible for the illness, Legionella, lives naturally in freshwater environments and can thrive in both natural and man-made water systems. While Legionella is often linked to artificial water systems like cooling towers or hot tubs, it can also be found in natural bodies of water, where it survives in association with amoebas.

The disease earned its name after a mysterious outbreak at an American Legion convention in Philadelphia in 1976, where many veterans became ill with severe pneumonia. Scientists eventually traced the outbreak to bacteria growing in the hotel’s air conditioning system. Since then, we’ve learned that Legionella bacteria can spread through tiny water droplets small enough to inhale deeply into the lungs.

People over 50, smokers, and those with weakened immune systems or chronic health conditions face higher risks from Legionnaires’ disease. Unlike many respiratory infections, it doesn’t spread from person to person. Instead, each case comes from direct exposure to contaminated water sources.

The illness typically starts with flu-like symptoms—fever, chills, and muscle aches—before progressing to a serious form of pneumonia. What makes diagnosis tricky is that these symptoms overlap with many other respiratory infections. Without specific testing, doctors can miss the true cause, potentially delaying proper treatment.

“Legionella infection represents a public health hazard owing to its ability to spread through exposure to natural water bodies and human-made water reservoirs,” writes Dr. Ashley Bryson, an internal medicine resident at the University of Manitoba, with coauthors.

The patient recovered after receiving targeted antibiotics, but his case serves as a reminder about the hidden risks that can exist in everyday activities. While this shouldn’t discourage anyone from enjoying recreational water activities, it underscores the importance of seeking medical attention when respiratory symptoms develop after potential exposure to various water sources, especially for those with higher risk factors.