Legionnaires’ disease ID’d as cause of secondary CAD

Legionella pneumonia diagnosed in rare case of CAD in 40-year-old man

Margarida Maia, PhD avatar

by Margarida Maia, PhD |

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Legionnaires’ disease — a lung infection caused by a group of bacteria called Legionella — caused secondary cold agglutinin disease (CAD) in a 40-year-old man, a case study reports.

The case, which represents the second reported case of CAD secondary to Legionnaires’ disease, suggest doctors should consider this infection as a possible cause of the rare autoimmune disease, the researchers noted.

The report, “A Rare Case of Cold Agglutinin Syndrome Associated With Legionella Pneumonia,” was published in Cureus.

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CAD occurs due to the abnormal production of self-reactive antibodies that cause red blood cells to agglutinate (stick together) at cold temperatures. This marks the cell clumps to destruction, leading to anemia, which happens when there aren’t enough red blood cells to carry oxygen around the body.

People with CAD may experience symptoms such as fatigue, shortness of breath, and pale skin.

The disease can be primary (when the cause is unknown) or secondary, when it occurs as a result of an underlying condition such as another autoimmune disease, a cancer, or an infection.

The most common infectious causes of secondary CAD are Mycoplasma pneumoniae, a bacterium involved in respiratory infections, and the Epstein-Barr virus (EBV), which causes infectious mononucleosis, or “mono.”

Rare case of secondary CAD

Now, a team of researchers in the U.S. described the rare case of a 40-year-old man who developed CAD secondary to Legionnaires’ disease, also known as Legionella pneumonia. Pneumonia is a lung condition characterized by inflammation and fluid in the lungs caused by a bacterial, viral, or fungal infection.

Legionella is a harmful type of bacteria that lives in fresh water, but can be caught from the environment, such as through breathing in contaminated water droplets.

The lungs are its most common site of infection, being “a well-known causative agent for community-acquired pneumonia that can lead to a severe disease requiring hospitalization,” the researchers wrote.

Identifying this infection can be difficult because it resembles other types of pneumonia, so doctors need to be vigilant in considering Legionella as a possible cause.

The man had experienced shortness of breath and fever for two days. His blood oxygen levels, measured with a portable device at home, showed low levels, prompting his visit to the hospital’s emergency department.

His skin appeared pale and he had discomfort in his belly region. He hadn’t been traveling or in contact with anyone who was sick. At the warehouse where he worked, he didn’t handle any toxic substances, but he was exposed to air conditioning, which can be a source of Legionella if it uses water to cool the air.

On examination, his blood pressure was normal, but his heart rate was faster than usual. When doctors listened to his lungs with a stethoscope, they heard crackling sounds on the right side — a potential sign of pneumonia.

Red blood cell agglutination

He had low levels of hemoglobin, the oxygen-carrying protein found in red blood cells and a sign of anemia. A sample of his blood cells observed under a microscope showed red blood cell agglutination, suggesting the presence of CAD.

After receiving fluids to help with hydration, his hemoglobin levels dropped further. He received warm blood transfusions and was kept warm with blankets and heating.

“Supportive care by keeping the patient warm is the first line of treatment,” the researchers wrote, adding that “supportive care while treating the underlying cause of his [CAD] was sufficient.”

A chest X-ray revealed pneumonia affecting multiple parts of the lungs. He was admitted to the hospital and was started on broad-spectrum antibiotics to treat community-acquired pneumonia.

A test for Legionella bacteria in his urine came back positive, but he tested negative for a panel of other respiratory bacteria and viruses. He then was started on a more specific antibiotic, azithromycin.

On the second day in the hospital blood testing no longer showed red blood cell destruction and showed mild increase in hemoglobin levels.

“He was monitored for one additional day given the degree of his anemia, and ultimately discharged on hospital day 3,” the researchers wrote.

Condition underdiagnosed?

There is “only one” other published report of secondary CAD related to Legionella bacteria, the researchers wrote, adding that “this raises the possibility of underdiagnosis” of CAD secondary to Legionella.

While secondary CAD “is generally associated with Mycoplasma species, Legionella pneumonia should be considered as well” in patients presenting “with atypical pneumonia and new onset anemia,” the researchers wrote.

“In addition to the appropriate selection of antibiotics, supportive measures, specifically keeping the patient warm, should be implemented,” the team concluded.