| Clinical
Features |
Legionnaires' disease, (LD), is
the more severe form of legionellosis and is characterized
by pneumonia, commencing 2-10 days after exposure. Pontiac
fever is an acute-onset, flu-like, non-pneumonic illness,
occuring within a few hours to two days of exposure. |
| Etiologic
Agent |
Legionella pneumophila and
other Legionella species. At least 46 species and 70
serogroups have been identified. L.pneumophila, an
ubiquitous aquatic organism that thrives in warm environments
(32°- 45°C) causes over 90% of LD in the United States. |
| Incidence |
An estimated 8,000-18,000 cases
occur each year in the United States, but only a fraction
of these are reported. Most LD cases are sporadic; 23% are
nosocomial and 10%-20% can be linked to outbreaks. Pontiac
fever has been recognized only during outbreaks. |
| Sequelae |
Death occurs in 10%-15% of LD cases:
a substantially higher proportion of fatal cases occur during
nosocomial outbreaks. Pontiac fever is a self-limited disease
that requires no treatment. |
| Transmission |
Inhalation of contaminated aerosols
from devices such as cooling towers, showers, and faucets,
and aspiration of contaminated water. Person-to-person transmission
does not occur. |
| Risk
Groups |
The elderly, cigarette smokers,
persons with chronic lung or immunocompromising disease, and
persons receiving immunosuppressive drugs. |
| Surveillance |
LD is a reportable condition in
most states; because of under-diagnosis and underreporting,
however, only 2%-10% of estimated cases are reported. |
| Trends |
Increasing awareness among physicians
and use of more sensitive, noninvasive tests such as urine
antigen testing has led to improved recognition of sporadic
cases and outbreaks caused by L. pneumophila, serogroup
1. Decreased use of culturing may be hampering recognition
of infections caused by Legionella species and serogroups.
|
| Challenges |
Diagnosis of legionellosis requires
specialized testing. Optimal methods for prevention of legionellosis
are not known, and source of most sporadic cases is unknown.
Rapid detection of travel-related legionellosis is needed
to identify potentially preventable disease transmission. |
| Opportunities |
Tests with improved sensitivity
have been developed but more are needed. Improved understanding
of ecology of Legionella can increase the effectiveness
of prevention and control measures. |
|
December 2003
|
