Legionellosis: DBMD


Article title: Legionellosis: DBMD
Conditions: Legionellosis, Pontiac fever
Source: DBMD

Legionnaire's Disease (LD) and Pontiac Fever

Clinical Features Legionnaires' disease, (LD), is the more severe form of legionellosis and is characterized by pneumonia. Pontiac fever is an acute-onset, flu-like, non-pneumonic illness.
Etiologic Agent Legionella pneumophila and other Legionella species. At least 46 species and 68 serogroups have been identified. L.pneumophila, an ubiquitous aquatic organism that thrives in warm environments (32- 45oC) causes over 90% of LD in the United States.
Incidence An estimated 8,000 - 18,000 cases occur each year in the United States; 23% are nosocomial. Most LD cases are sporadic; 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 2001


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