This document summarizes Legionella pneumophila, the bacteria that causes Legionnaires' disease. It describes the 1976 outbreak in Philadelphia that led to the discovery of the disease. Legionella pneumophila is a thin, pleomorphic gram-negative rod that is difficult to visualize with gram staining. It grows on charcoal yeast extract agar and is strictly aerobic. The bacteria is found in aquatic environments and transmitted via air. Legionnaires' disease presents as acute pneumonia while Pontiac fever causes flu-like symptoms without pneumonia. Diagnosis involves isolation of the bacteria or increasing antibody titers in serology tests. Erythromycin and rifampin are the recommended treatments.

1. NON-ENTERIC GRAM NEGATIVE RODS
Legionella and Bacteroides

2. I. Legionella pneumophila
LEGIONAIRES’ DISEASE AND PONTIAC FEVER

3. In August of 1976 at an American Legion Convention
Philadelphia more than 200 members were stricken with
an unknown respiratory illness with an abrupt onset of
fever, chills, headache, cough, and progressive multi-
lobar pneumonia. Many became confused and comatose
with multi-organ failure (especially GI, CNS, liver and
kidneys).
Thirty four (34) individuals died from this outbreak (17%).

4. A.CHARCTERISTIC PROPERTIES OF
Legionella pneumophila
1. A difficult organism to visualize in clinical material (A).
It does not stain well with the Gram stain. In culture,
L. pneumophila is a thin, pleomorphic Gram negative rod (B).
A B

5. 2-4. Legionellae are visualized best using modified
Giemsa, silver impregnation, or immunofluorescent
staining (below).
Since they are facultative intracellular pathogens,
legionellae are typically seen in macrophages.

6. 5. Legionella pneumophila grown on a charcoal buffered
yeast extract agar with L-cysteine (BCYE).
6. Incubated for 5 days at 37OC aerobically with 5% CO2

7. 7. Legionella are strictly aerobic, catalase positive, and
weakly oxidase positive.
8. There are at least 4 serogroups.
(most human infections are caused by Serogroup I)
Characteristics (Cont.)

8. B. EPIDEMIOLOGY: Legionella pneumophila
1. Environmental Isolates mostly from aquatic sources
such as air conditioning systems, rivers, lakes, ponds,
and tap water (including samples of distilled water).
2. These organisms are not found normally in animals
( NOT ZOONOTIC AGENTS).
3. Causes Legionaires’ Disease as an endemic, sporadic,
point source outbreak: Also causes Pontiac Fever.
4. Incubation period for Legionaires’ Disease is 2-10 Days.
5. Low attack rate of 0.1 to 4% of those exposed.
6. In contrast, Pontiac Fever has a high attack rate
> 95% of those exposed with a short incubation period
of 6 hours to 2 days. (NO PNEUMONIA)
7. Worldwide incidence
8. More prevalent in summer
9. Affects middle aged to elderly males most frequently.
10. Spread by airborne transmission (not Human to Human).

9. C. CLINICAL MANIFESTATIONS: 2 FORMS OF DISEASE
LEGIONAIRES’ DISEASE AND PONTIAC FEVER
LEGIONAIRES’ DISEASE
Portal of entry is respiratory
Acute fibrinopurulent
bronchopneumonia
May have Bacteremia
May vary from mild to severe
fulminant systemic disease
and death
PONTIAC FEVER
Acute, self limited, febrile
NOT FATAL
Abrupt onset, myalgia,
malaise, headache
NO PNEUMONIA
May be asymptomatic
Recover in 2 to 5 days

10. D. DIAGNOSIS
1. Diagnosis can be problematic, since definitive
diagnosis depends upon isolation and identification
of L. pneumophila from the appropriate clinical
material.
2. Serology is a quick way to make a tentative diagnosis,
utilizing increasing antibody titers (> 4 fold), however
immunofluorescent staining, hemagglutination,
hemagglutination inhibition, micro-agglutination
and ELISA may all be used to augment diagnosis.

11. E. THERAPY
Erythromycin and Rifampin are the drugs of choice;
DO NOT USE Cephalosporins, Tetracyclines,
Clindamycin or Vancomycin

12. II. More that 39 species in the genus
Legionella
Many cause a pneumonia similar to Legionaires’ disease,
e.g. L. micdadei and L. bozemaniae.
In addition to Legionella, there are a large number of
miscellaneous Gram negative rods that cause serious to
fatal infections in Humans.
These are too numerous to list here, but include
important pathogens such as in the genus Bartonella.