Infectious Disease Compendium



Gram negative aerobes. Besides L. pneumophila, there are L. anisa, L. birminghamensis, L. bozemanii, L. cincinnatiensis, L. dumoffii, L. feeleii, L. gormanii, L. hackeliae, L. jordanis, L. lansingensis, L. longbeachae, L. maceachernii, L. micdadei, L. oakridgensis, L. parisiensis, L. sainthelensi, L. tucsonensis, L. wadsworthii to name a few. Or a lot.

There are 64 serogroups in the family, for L. pneumophila there are 15 serogroups, serogroups 1, 4, and 6 account for most human disease.

Epidemiologic Risks

Found in water of all kinds especially warm water like shower heads, fountains, hotel pools, hot tubs, and the like. Often outbreaks in cruise ships (combined with the Norwalk agent, they get you at both ends).

Multiple studies have demonstrated that Legionella rates go up after rains (PubMed), especially with warm humid weather (PubMed).

One strain in the Netherlands, Legionella pneumophila sequence type 47, is perhaps in dirt (PubMed).

L. longbeachae infections are increasing. Transmission is associated with soils, composts, and potting mixes rather than with water systems (PubMed). And bringing your dirty, composty hands near your face transmits the disease, so good hand hygiene for gardeners (PubMed).

May be increased in them what get TNF antagonists. Up to 20% may be associated with travel.

There have been outbreaks with cooling towers and air scrubbers that can spread the organisms for up to 10 kilometers (PubMed). It is increased shortly after hot, humid, thundershower weather (PubMed) and is easily found in roadside puddles after a rain. There was an outbreak traced to an asphalt paving machine. Even smoking dope was a risk in one study. And humidifiers (PubMed). And industrial pressure test pumps (PubMed). And even car windshield washer fluid. If there is water, there is Legionella.

It may be lurking in your hospitals ancient pipes.

A street cleaning trucks (PubMed) so cleaning up the Bourbon street vomit could be spewing Legionella into the air.

It is a common cause of pneumonia in Germany (and maybe elsewhere) (PubMed).

"Overall, incidence of Legionnaires’ disease in the city of New York increased 230% from 2002 to 2009 and followed a socioeconomic gradient, with highest incidence occurring in the highest poverty areas. Among patients with community-acquired cases, the probability of working in transportation, repair, protective services, cleaning, or construction was significantly higher for those with Legionnaires’ disease than for the general working population (PubMed)."

Biologics increase the risk for PJP, but also for Listeria, Salmonella, and Legionella and it has been suggested that all patients on biologics be on TMP/Sulfa to prevent all of the above (PubMed).

And there was the horrible case of the child who died from Legionella after a water birth (PubMed).


L. pneumophila: Pneumonia.

When the CXR shows patchy infiltrates and the sputum has WBC but no organisms seen, think atypical and when you think atypical, think Legionella.

Pontiac Fever: a 'flu' like illness without pneumonia usually after exposure to water and can be diagnosed with the urinary antigen (PubMed). It is also a rare cause of endocarditis. The other legionella also cause pneumonia and (culture negative) endocarditis.

L. feeleii: case report of cellulitis.


Culture (usually will not grow), serology and Legionella urinary antigen which only gets serogroup 1 Legionella pneumophila.

PCR if used routinely can markedly increase the diagnosis, in one study it went from 1 in 9 to 1 in 20 cases of pneumonia (PubMed).


Azithromycin, ciprofloxacin, levofloxacin, tmp/sulfa and tetracycline have all been successful. Maybe quinolones are best. Or maybe not; no mortality difference between quinolone and macrolide (PubMed). Combine with rifampin for severe cases.

Tigecycline may be a good second line agent, either alone or with other antibiotics (PubMed).


There is one case of person to person spread, a mother who took very good care and close of her infected son in Portugal.

There have been at least three cases, and one death, in newborns who were subjected to drowning, er, I mean water birth. People sure can be creative in coming up with ways to harm themselves and others (PubMed).

In the wild Legionella lives in amoebas.

Unfortunatly its ideal temperature growth range is the same as ours: 90 to 108 °F.

Curious Cases

Relevant links to my Medscape blog

Zebras are so last century


Little things

Batting 126

Order Everything, Get Something in Return

Summer Time and the Living is Infected.



Soaked and Sodden Infections

Last Update: 04/03/18.