by Chandana Balasubramanian
Pathogen of the month: Legionella
Doubt strikes fear into the hearts of many. But it is a powerful tool in the hands of medical professionals and researchers. Being uncertain is the impetus that drives truth-seeking peer-to-peer verification and differential diagnoses that can help save lives.
Take Legionnaires’ disease. It is one of the leading causes of pneumonia worldwide . If left untreated without the right antibiotics, it can be fatal. In the United States alone, the economic burden of just one year of Legionnaires’ disease cases can be over 800 million US dollars .
Surprisingly, it is often overlooked. So much so that even the World Health Organization or WHO states, “Since many countries lack appropriate methods of diagnosing the infection or sufficient surveillance systems, the rate of occurrence is unknown. In Europe, Australia, and the USA, there are about 10–15 cases detected per million population per year .”
A great place to begin addressing these challenges is if clinicians are willing to embrace doubt when faced with diagnosing pneumonia-like symptoms.
What causes Legionnaires’ Disease or Legionellosis?
There were many historical events in 1976. NASA unveiled their first space shuttle, Apple Computers was born, and the first Rocky movie was released. Unfortunately, it was also the year a tragic event led to the discovery of Legionnaires’ disease.
On July 21st, 1976, 4000 delegates from the American Legion, America’s largest veterans’ service organization, traveled to Philadelphia for a convention. Within a few weeks, almost 200 got sick with an upper respiratory illness, and 29 died. It took nearly five months of investigations to identify the pathogen – Legionella – as the cause .
Legionnaires’ disease or Legionellosis is caused by the bacteria Legionella. It lives in water and soil and can cause health issues when it grows in showerheads and faucets, hot tubs, and in stagnant water and air conditioning systems in large buildings. We are susceptible to infection by Legionella when we inhale water droplets with the bacteria in it or come in contact with contaminated soil. Legionellosis is not spread through direct human-to-human transmission. It has an incubation period of 2 to 10 days.
Legionella is widely found in warm water environments, so most cases of Legionnaires’ occur in the summer and early autumn. Legionnaires’ is a public health issue. Cassell et al. caution that utmost care must be taken when COVID-19 restrictions are lifted worldwide. Going back to work or school in buildings left unoccupied or unused during lockdowns is a risk factor for Legionellosis .
Why is Legionnaires’ Disease often misdiagnosed or overlooked?
According to Reller et al. , a wrong Legionellosis diagnosis is often due to:
- The inability to distinguish Legionnaires’ disease from other types of pneumonia, clinically and radiographically,
- Failure to order diagnostic tests for Legionella infection, and
- Inadequacies in current diagnostic tests and protocols.
The majority of Legionnaires’ disease cases each year remain undiagnosed; the world still awaits better diagnostic tests and protocols for Legionellosis. But the issue of “failure to order diagnostic tests for Legionella infections” can be fixed. The Urine Antigen Test (UAT) and sputum tests prescribed for Legionella are inexpensive, so cost is not the issue.
The solution lies in training medical professionals to embrace doubt and challenge their confirmation biases. Clinicians who take a few minutes to input a patient’s pneumonia and accompanying symptoms on a robust, clinical decision support tool like GIDEON (Global Infectious Diseases and Epidemiology Network) can better understand how to proceed.
For example, when the COVID-19 pandemic hit, experts cautioned clinicians to be on the alert for Legionellosis as well. The concern was that clinicians might repeatedly be testing community-acquired pneumonia patients for COVID-19 but not Legionellosis – which would delay diagnosis and treatment. Since initial clinical presentations for the two are similar, clinical decision tools can be extremely useful.
GIDEON, for example, has a built-in feature to help clinicians challenge their confirmation biases. A ‘Why Not?’ feature helps clinicians understand why a specific diagnosis does not show up on the list of probable causes of a patient’s symptoms.
Legionnaires’ disease, misdiagnosed as Malaria, can be fatal because malarial drugs do not work against Legionella. It is even more critical to get the right diagnosis early.
Legionellosis Misdiagnosed as Malaria
Take the example of the agricultural expert from Israel wrongly diagnosed with malaria instead of Legionellosis. He had traveled to India to work on a farming project in 2005. A week later, when he returned to Israel, he developed fever, headache, vomiting, and muscle pain. In two days, he felt better, but the symptoms reappeared but with cough, shortness of breath, and rigors in tow. The patient was highly lethargic, hypotensive, and blood tests showed elevated bilirubin and creatinine levels.
Because of his recent travel to India, doctors thought it was Malaria. He was started on malarial medication while laboratory tests were being processed. But when blood smears proved negative for Malaria, his doctors wondered if it was Dengue.
Luckily for him, his doctors decided to challenge their cognitive biases and conducted a differential diagnosis. They entered the patient’s symptoms in the popular DDx or differential diagnosis tool, GIDEON. To their surprise, neither Malaria nor Dengue showed up as possibilities. But given the symptoms and the incubation period, Legionellosis turned out to be the prime (and accurate) suspect. This saved his life because standard malarial therapy does not work against Legionellosis.
Misdiagnosing Legionnaires’ disease can be fatal, lead to a public health crisis, and add hundreds of millions to an already astronomically high healthcare burden. One of the main reasons it is often overlooked is that clinicians may not think about testing for Legionellosis when treating a patient with pneumonia.
Equipping clinicians with the right clinical diagnosis tools can help them validate their assumptions. Not only that, using a tool like GIDEON, clinicians can also challenge their confirmation biases and learn why a diagnosis does not apply to a specific set of symptoms.
Getting to the correct answer starts with harboring and encouraging healthy doubt in initial diagnoses. As the famous philosopher, Voltaire said, “Doubt is not a pleasant condition, but certainty is absurd.”
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|||WHO, World Health Organization, “Fact Sheet: Legionellosis,” WHO, February 16th, 2018. [Online]. Available: https://www.who.int/news-room/fact-sheets/detail/legionellosis. [Accessed 08 07 2021].|
|||K. R. C. E. a. S. C. M. Baker-Goering, “Economic Burden of Legionnaires’ Disease, United States, 2014,” Emerg Infect Dis., vol. 27, no. 1, pp. 255-257, 2021.|
|||J. E. M. e. al., “Legionnaires’ disease: Isolation of a bacterium and demonstration of its role in other respiratory diseases,” N. Engl. J. Med., vol. 297, no. 22, pp. 1197-1203, 1977.|
|||K. Cassell, “Legionnaires’ disease in the time of COVID-19,” Pneumonia, vol. 13, 2021.|
|||L. R. e. al., “Diagnosis of Legionella Infection,” Clinical Infectious Diseases, vol. 36, no. 1, pp. 64-69, 2003.|