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| Division of Bacterial and Mycotic Diseases |
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| Home > Home > Disease Listing > Legionellosis
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Legionellosis:
Legionnaires' Disease (LD) and Pontiac Fever
| 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. |
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Date: October 12, 2005
Content source: Coordinating Center for Infectious Diseases / Division of Bacterial and Mycotic Diseases |
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