Legionnaires Disease: the Clinician's Myth

by John Herbert

Legionnaires’ Disease is vastly under reported and under diagnosed, but why? Europe’s ECDC article clearly explains how it is under diagnosed (https://legionnaires.ecdc.europa.eu/?pid=109)

Also this June 2023 article (https://www.ccjm.org/content/ccjom/90/6/345.full.pdf ) nicely explains, conducting a Legionnaires’ Disease test would not change the recommended treatment, so it’s an unnecessary expense.

That’s faulty logic, and perpetuates the myth that Legionnaires Disease is rare. It can only be detected by testing, but testing is unnecessary/too expensive, as a consequence there are no positive test results logged, so that means it must be uncommon?

However, if the traditional CAP (Community Acquired Pneumonia) regime fails, and the patient(s) deteriorate, which is really bad news for the elderly age group, then they may test.

That article, and many more like it, explain that its complicated, patients presenting with CAP (Community Acquired Pneumonia) are immediately treated with antibiotics, many recovering before there is any thought about possible sources. However, the elderly, the most susceptible in society to illness, often don’t survive.

Again under-reporting / under-diagnoses is mentioned in the more recent paper in the Lancet April 2025 ( https://www.thelancet.com/journals/lanmic/article/PIIS2666-5247(24)00299-4/fulltext ) No wonder, since clinicians don’t test.

There are about 8,000 CAP cases every month in Hong Kong which should raise alarm bells, considering its the second highest cause of death!