County of Los Angeles
Department of Public Health
Acute Communicable Disease Control
313 N. Figueroa Street, Room 212
Los Angeles, CA 90012
Phone: (213) 240-7941
Fax: (213) 482-4856
E-Mail:acdc2@ph.lacounty.gov
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Acute Communicable Disease Control
Legionellosis
Legionellosis is a bacterial infection with two distinct clinical forms: 1) Legionnaires’
disease (LD), the more severe form characterized by pneumonia, and 2) Pontiac fever, an acute-onset,
self-limited flu-like illness without pneumonia. Legionella bacteria are common inhabitants of
aquatic systems and thrive in warm environments. Ninety percent of cases of LD are caused by
Legionella pneumophila, although at least 46 Legionella species and 70 serogroups have been
identified. Transmission occurs through inhalation of aerosols containing the bacteria or by
aspiration of contaminated water. Person-to-person transmission does not occur. The case
fatality rate for LD ranges from 10%–15%, but can be higher in outbreaks occurring in a
hospital setting. People of any age may get LD, but the disease most often affects middleaged
and older persons, particularly those who are heavy smokers, have chronic lung disease, or whose
immune system is suppressed by illness or medication.
Legionellosis is a bacterial infection with two distinct clinical forms: 1) Legionnaires’
disease (LD), the more severe form characterized by pneumonia, and 2) Pontiac fever, an acute-onset,
self-limited flu-like illness without pneumonia. Legionella bacteria are common inhabitants of
aquatic systems and thrive in warm environments. Ninety percent of cases of LD are caused by
Legionella pneumophila, although at least 46 Legionella species and 70 serogroups have been
identified. Transmission occurs through inhalation of aerosols containing the bacteria or by
aspiration of contaminated water. Person-to-person transmission does not occur. The case
fatality rate for LD ranges from 10%–15%, but can be higher in outbreaks occurring in a
hospital setting. People of any age may get LD, but the disease most often affects middleaged
and older persons, particularly those who are heavy smokers, have chronic lung disease, or whose
immune system is suppressed by illness or medication.
