Bacteria that cause Legionnaires’ disease are not uncommon

By Chris Healey

Legionellosis is on the rise in the United States.

A recent study published in Environmental Science & Technology described the presence of Legionella pneumophila in nearly half of the 272 water samples collected across the United States. The presence of L. pneumophila in well water is alarming because it can infect humans if the water becomes aerosolized.

Widespread detection of L. pneumophila in well water coincides with increasing cases of the illness. Health departments across the U.S. have reported rising rates of legionellosis.

L. pneumophila causes Legionellosis—an overarching term given to two clinically and epidemiologically distinct illnesses. Legionnaires’ disease is characterized by fever, myalgia, cough, and clinical or radiographic pneumonia. Pontiac fever is characterized by milder versions of same symptoms of Legionnaires’ disease with no pneumonia. Infection occurs after inhalation of bacteria or bacterial antigen aerosolize in a mist or spray. The disease is noncommunicable; it cannot be spread from person to person.

Symptoms of Legionnaire’s disease begin 2 to 10 days after exposure, but symptoms often appear in 5 to 6 days. Most cases of Legionnaires’ disease can be treated with antibiotics, specifically fluoroquinolones or macrolides. Hospitalization is often required, with a case fatality rate as high as 15%. Most individuals exposed to Legionella will show no symptoms of infection, or only experience a mild illness.

Those at greatest risk of developing symptoms include the elderly, current or former smokers, those with chronic lung disease, immunocompromised individuals, and those taking immunosuppression drugs.

Pontiac fever is a self-limited, non-lethal febrile illness that does not progress to pneumonia. Symptoms of appear 5 to 72, but most often 24 to 48, hours after antigen exposure and usually lasts 2 to 5 days. Antibiotics do nothing to alleviate Pontiac fever. Patients recover spontaneously without treatment.

According to the CDC, L. pneumophila colonizes the lungs and is difficult to diagnose. Bacterial isolation, direct fluorescent antibody testing, urine antigen, and serology can all be used to test for infection.

L. pneumophila gets its name from its manner of discovery. The bacterium was isolated and identified among members of the Pennsylvania American Legion who were attending a conference in Philadelphia in 1976. Of the 182 members who developed acute illness, 29 died.

Although it was discovered and named in 1976, the bacterium was isolated about 25 years earlier. L. pneumophila has been confirmed as the causative agent of outbreaks dating back to 1959.

Since there is no vaccine for legionellosis, prevention stems from maintaining warm water sources. Commercial cooling towers should be drained and scale and sediment removed when not in use. Hot water tanks should be maintained at a temperature greater than 122 degrees Fahrenheit. Hot tub and whirlpool maintenance should follow manufacturer recommendations. Hot tubs, for example, should have bromide levels between 4 and 6 parts per million, while pH should be kept slightly basic – between 7.2 and 7.8.

The natural presence of L. pneumophila also poses a security concern. Soviet scientists working on the Soviet bioweapons program reported they had genetically modified L. pneumophila to be more lethal. The possibility exists that modern state or non-state actors could modify the bacteria in a similar way for malicious purposes.


Image Credit: Wikimedia Commons/ JJ Harrison