Att 13_Treating Clinician_Test materials

What Clinicians Need to Know about

LEGIONNAIRES’ DISEASE

Legionnaires’ disease is a sometimes fatal form of pneumonia that is on the rise in the United States.
Unfortunately, this disease is also underrecognized and underdiagnosed. Clinicians are in a unique position
to make sure cases are detected, allowing rapid investigation by public health officials and prevention of
additional cases.

•

Patients with Legionnaires’ disease, no matter where they acquired
the infection

•

Positive environmental tests for Legionella

•

Changes in water quality that may lead to Legionella growth (such as low
chlorine levels)

The preferred diagnostic tests for Legionnaires’ disease are culture of lower
respiratory secretions on selective media and the Legionella urinary antigen test.
Serological assays can be nonspecific and are not recommended in most situations.
Best practice is to obtain lower respiratory specimens for culture at the time urinary
antigen testing is ordered, preferably before the administration of antibiotics. The
urinary antigen test detects Legionella pneumophila serogroup 1, the most common
cause of Legionnaires’ disease; isolation of Legionella by culture is important for
detection of other species and serogroups and for public health investigation.
Molecular techniques can be used to compare clinical isolates to environmental
isolates and confirm the outbreak source.
If your patient has Legionnaires’ disease, see the most recent guidelines for treatment
of community-acquired pneumonia:
http://cid.oxfordjournals.org/content/44/Supplement_2/S27.full.

1.2
1
0.8
0.6
0.4
0.2
2014

2013

2012

0
2011

Clinicians should also test patients with healthcare-associated pneumonia for
Legionnaires’ disease. This is especially important among patients at increased risk
for developing Legionnaires’ disease, among patients with severe pneumonia (in
particular those requiring intensive care), or if any of the following are identified in
your facility:

1.4

2010

Patients with a travel history within 2 weeks before the onset of illness

1.6

2009

•

1.8

2008

Patients with pneumonia in the setting of a Legionnaires’ disease outbreak

2007

•

National incidence of legionellosis
2000–2014*

2006

Immunocompromised patients with pneumonia

2005

•

2004

Patients with severe pneumonia, in particular those requiring intensive care

2003

•

2002

Patients who have failed outpatient antibiotic therapy for community-acquired
pneumonia

2001

•

Incidence (cases/100,000 pop.)

Clinical features of Legionnaires’ disease include cough, fever, and radiographic
pneumonia. Signs and symptoms for Legionnaires’ disease are similar to pneumonia
caused by other pathogens; the only way to tell if a pneumonia patient has
Legionnaires’ disease is by getting a specific diagnostic test. Indications that warrant
testing include:

Use both a urinary
antigen test and culture
of a lower respiratory
specimen when testing
patients for Legionella.

2000

Diagnosis, Testing, and Treatment

Year

Between 2000 and 2014, 286% increase in legionellosis (based on NNDSS*)
*National Notifiable Disease Surveillance System

In the United States, reported
cases of Legionnaires’ disease
have grown by nearly four times
since 2000. About 5,000 cases
of Legionnaires’ disease are now
reported to CDC each year, but this
number is likely an underestimate
as the illness is thought to be
underdiagnosed.
More illness occurs in the summer
and early fall, but Legionnaires’
disease can happen any time
of year.

Reporting
Timely identification and reporting of cases is important, as this allows public health
officials to quickly identify and stop potential clusters and outbreaks by linking new
cases to previously reported ones. Most investigations examine where patients may
have been exposed to contaminated water during the 14 days before symptoms
began. The incubation period for Legionnaires’ disease is typically 2–10 days, although
cases have been reported with onset up to 19 days after exposure. Healthcare facility
exposures are important to document; because many people receiving treatment in
hospitals are highly susceptible to Legionella, even a short stay can result in infection.
Inpatient, outpatient, employee, and visitor exposures to healthcare settings should be
quickly reported to ensure that steps can be taken to prevent further cases. Outbreaks
among travelers are common but can be difficult to detect because of the low attack
rate and the dispersal of people from the source of the outbreak, so collecting and
reporting information about overnight travel in the 14 days prior to onset is needed
for public health officials to link cases together.

Etiology
Legionnaires’ disease is a severe form of pneumonia that often requires hospitalization
and is fatal in about 10% of cases. Legionnaires’ disease is caused by Legionella
bacteria. There are at least 60 different species of Legionella, and most are considered
capable of causing disease. However, most disease is caused by L. pneumophila,
particularly serogroup 1.

Timely reporting of
Legionnaires’ disease
cases is important for
controlling clusters and
outbreaks.

Commons Sources
of Infection
Outbreaks of Legionnaires’ disease
are most often associated with
large or complex water systems,
like those found in hospitals, longterm care facilities, hotels, and
cruise ships.
The most likely sources of
infection include:
Water used for showering
(potable water)

Transmission
While Legionella is found in natural, freshwater environments, it can become a health
concern in human-made water systems (e.g., plumbing system of large buildings,
cooling towers, decorative fountains, hot tubs) where conditions allow it to multiply
and come in contact with vulnerable persons. People contract Legionella by inhaling
aerosolized water droplets containing the bacteria, or, less commonly, by aspiration
of contaminated drinking water. Legionella is usually not transmitted from person
to person; however, a single episode of person-to-person transmission has been
reported. Fortunately, most people exposed to the bacteria do not become ill.

Risk Factors
Risk factors for developing Legionnaires’ disease include:
•

Renal or hepatic failure

•

Smoking (current or historical)

•

Diabetes

•

Immune system disorders

•

Chronic lung disease

•

Age ≥50 years

•

Systemic malignancy

Prevention
The key to preventing Legionnaires’ disease is maintenance of the water systems in
which Legionella may grow. If Legionella is found in a healthcare facility’s water system,
the facility should be prepared to eliminate the bacteria. CDC encourages all building
owners, and especially those in healthcare facilities, to develop comprehensive water
management programs to reduce the risk of Legionella growth and spread.

cdc.gov/legionella

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CS262589-C

05/13/2016

Cooling towers (parts of large
air conditioning systems)

Decorative fountains

Hot tubs