Legionellosis

Table of Contents

Disease Information

Overview

Legionellosis is an infection caused by Legionella species, with Legionella pneumophila being the most common.

Also known as:  Legionnaires’ disease

Responsibilities

  • 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 HHS
Disease Reporting Hotline: (800) 362-2736
Secure Fax:  (515) 281-5698

A. Agent

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.

C. Reservoirs

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.  

G. Epidemiology

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

None.

I. Additional Information

The Council of State and Territorial Epidemiologists (CSTE) surveillance 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.)

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