Also known as: Legionnaires’ disease
Hospital: Report by IDSS, facsimile, mail, or phone, follow-up required
Lab: Report by IDSS, facsimile, mail, or phone
Physician: Report by facsimile, mail, or phone
Local Public Health Agency (LPHA): Follow-up required
Iowa Department of Public Health
Disease Reporting Hotline: (800) 362-2736
Secure Fax: (515) 281-5698
Legionellosis is an infection caused by Legionella species, with Legionella pneumophila being the most common. Numerous serogroups are commonly recognized, although Legionella pneumophila serogroup 1 is most commonly associated with serious illness.
B. Clinical Description
Symptoms: Legionellosis has two distinct forms: Legionnaires’ disease, which is the more severe form of the infection, and Pontiac fever, which is milder. The most common initial symptoms for Legionnaires’ disease and Pontiac fever are anorexia, myalgia, malaise and headache. This is rapidly followed by fever (up to 102 - 105° F.), chills and a non-productive cough. Other symptoms may include abdominal pain and diarrhea.
Onset: Can be rapid.
Complications: Legionnaires’ disease is associated with pneumonia. The case-fatality rate overall is 5% -30%. Pontiac fever is not associated with pneumonia or death and cases usually recover in 2 - 5 days without treatment. Legionnaires’ disease usually cannot be distinguished from other forms of pneumonia and requires specific tests to confirm the diagnosis.
Common reservoirs: Legionella species are commonly found in the environment. They have been found in many different kinds of water and water systems, such as hot and cold-water taps and showers, creeks, ponds, whirlpool spas, and cooling towers and evaporative condensers of large air-conditioning systems. Outbreaks of legionellosis have been linked to these sources, as well as to decorative fountains, humidifiers, respiratory therapy devices and grocery store vegetable misters. These bacteria are most likely to reproduce in high numbers in warm, stagnant water, and its presence may be correlated with the presence of free-living amoeba.
D. Modes of Transmission
Airborne: Legionellosis is transmitted via the airborne route after inhalation of aerosols from water sources contaminated with the bacteria. There is no evidence to suggest transmission of Legionella from auto air-conditioners or household window air-conditioning units that do not use water as their coolant.
Person-to-person: Legionellosis is not transmitted from person-to-person.
E. Incubation period
The incubation period for Legionnaires’ disease is from 2 - 10 days, but most often 5 - 6 days.
The incubation for Pontiac fever is from 5 - 72 hours, but most often 24 - 48 hours.
F. Period of Communicability or Infectious Period
Legionellosis is not communicable from person-to-person. Water sources may continue to spread Legionella organisms until corrective treatment is completed.
Legionnaires’ disease was named after an outbreak that occurred in Philadelphia in 1976, among people attending a convention of the American Legion. Legionellosis has a worldwide distribution with cases reported from North America, Australia, Africa, South America and Europe. An estimated 8,000 to 18,000 people develop Legionnaires’ disease in the United States each year. Most of these are single, isolated cases not associated with an outbreak. Outbreaks usually occur in the summer and fall, though cases occur year-round. Serologic surveys have shown a prevalence of antibodies to Legionella pneumophila serogroup 1 at a titer of >1:128 in 1-20% of the population, thus many infections go unnoticed. The illness most often affects older people and males, especially those who smoke or have chronic lung disease. Other risk factors include immunosuppressive therapy and immunosuppressive diseases, such as AIDS and diabetes. Legionella is estimated to be responsible for between 0.5% - 5% of cases of community-acquired pneumonias.
H. Bioterrorism Potential
I. Additional Information
The Council of State and Territorial Epidemiologists (CSTE) surveillance case definitions for Legionellosis can be found at: www.cdc.gov/osels/ph_surveillance/nndss/phs/infdis.htm#top
CSTE case definitions should not affect the investigation or reporting of a case that fulfills the criteria in this chapter. (CSTE case definitions are used by the state health department and the CDC to maintain uniform standards for national reporting.)
American Academy of Pediatrics. 2003 Red Book: Report of the Committee on Infectious Diseases, 26th Edition. Illinois, American Academy of Pediatrics, 2003.
CDC. Guidelines for preventing health-care-associated pneumonia, 2003: recommendations of CDC and the Healthcare Infection Control Practices Advisory Committee (HICPAC). MMWR 2004;53(RR03):1-36.
CDC Website. Legionellosis: Legionnaires’ Disease and Pontiac Fever. www.cdc.gov/legionella/index.html
Heymann, D., ed. Control of Communicable Diseases Manual, 20th Edition. Washington, DC, American Public Health Association, 2015.
Fiore, A.E., et al. Epidemic Legionnaires’ Disease Two Decades Later: Legionellosis Sources, New Diagnostic Methods. Clinical Infectious Diseases. 1998; 26:426-433.