Legionella bacteria are intracellular pathogens – microparasites which cause disease by growing and reproducing inside the cells of a host. In this case, they cause community acquired diseases ranging from Pontiac fever, which is mild, to Legionnaires’ disease, which can be fatal . In the latter case, the early administration of the appropriate antimicrobial therapy is essential.
Legionnaires’ disease is a severe type of pneumonia, accounting for 1-10% of all cases of community-acquired pneumonia (CAP). Untreated, patients may develop lung complications. Recent statistics suggest that about 1 in 10 patients will never recover from these complications. This figure rises to 1 in 4 for patients who acquired Legionnaires’ disease in a healthcare facility.
On a brighter note, almost all cases of Legionnaires’ disease can be treated successfully – as long as the patient is otherwise healthy. There are, however, people who are at a higher risk of developing complications, including those who:
For most patients, the etiology (cause or origin of the disease) is unknown at diagnosis. So, empiric (guided by practical experience rather than theory) treatment is appropriate. At time of writing, Erythromycin, formerly the antibiotic of choice against Legionella, has been replaced by two classes of antibiotics which are proven to be more potent and less toxic.
Other effective agents include, tetracycline, doxycycline, minocycline and trimethoprim/sulfamethoxazole.
In many cases, treatment requires hospitalization, where the patient will be in the hands of a specialist in lung diseases (pulmonologist) or infectious diseases (pathologist). In severe cases, the patient may be admitted to intensive care. But for all cases, the sooner an appropriate therapy starts, the lower the chance the patient will develop complications.
Legionellosis can also present as Pontiac fever, which is treated differently. Much milder, Pontiac fever requires little medical intervention for the patient to make a full recovery.