NAME: Legionella pneumophila
CHARACTERISTICS: Legionella pneumophila is a gram negative, strictly aerobic bacterium of the Legionellaceae family(3). It exhibits poor staining and can appear in different forms. In lung or sputum samples, L. pneumophila appears as a small to short rod with a length of 3 to 5 μm. When cultured, it appears as a long filamentous bacillus with a length of 10-25 μm. The number of reported serogroups varies with the highest report at 16 recognized serogroups(3,4).
PATHOGENICITY/TOXICITY: L. pneumophila infection can cause Legionnaires' disease, a severe form of pneumonia(4,5). The symptoms of Legionnaire's disease include confusion, headache, diarrhoea, abdominal pain, fever, chills, and myalgia as well as a non-productive cough(5). Mortality rate is reported to be 15-25%(3,4).
Pontiac fever is a non-pneumonic form of L. pneumophila infection(2). Symptoms are flu-like, including fever, tiredness, myalgia, headache, sore throat, nausea, and cough may or may not be present. Pontiac fever is self limited and requires no hospitalization or antibiotic therapies(3). There are no reported deaths associated with Pontiac fever.
Although up to 85-90% of cases can be attributed to L. pneumophila , approximately half of the remaining 49 species in the genus have caused disease in humans(6). It is conjectured that up to 40% of cases involving these rare pathogens, attributed to species and groups other than L. pneumophila serogroup 1, are missed clinically if commercially available urine antigen detection kits, which target only L. pneumophila serogroup 1, are used exclusively for diagnosis(4).
EPIDEMIOLOGY: L. pneumophila is of worldwide prevalence(7). Infections are reported in North and South America, Asia, Australia, New Zealand, Europe and Africa. L. pneumophila is the cause of 1-2% of all pneumonia cases in adults(7). The number of cases reported increases in the summer and fall(1). During an epidemic of Pontiac fever, 95-100% of individuals exposed to the source develop infection. In contrast, during an epidemic of Legionnaire's disease, only 2- 7% of people exposed develop the infection(8). The prevalence of Legionnaire's disease in Canada is low, with approximately 75 cases reported annually. This is equivalent to 1.3-3.5 cases/ 1,000,000 people(9). The most common causative agent of LD is L. pneumophila serogroup 1 (Lp1)(9,10). Lp1 is responsible for 61-88% of reported cases. Further distinction between sequence types shows that sequence type 1 (ST1) is most commonly associated with LD(10).
INFECTIOUS DOSE: Unknown.
RESERVOIR: L. pneumophila is found naturally in most fresh water sources, including lakes, ponds, and rivers(1,12,13). It is found in cooling towers, plumbing systems, water heaters, and warm water spas(3,7). It has also been isolated from soil samples(14).
DRUG SUSCEPTIBILITY: L. pneumophila is susceptible to erythromyin, clarithromycin, azithromycin, tetracycline, moxifloxin, and levofloxacin(1,3). Aminoglycosides such as gentamicin, kanamycin and streptomycin are active against L. pneumophila(15,16); however, there are mutant strains that show resistance to streptomycin(17). Beta-lactam antibiotics (i.e. penicillin, cephalosporins) are ineffective against L. pneumophila(18).
SUSCEPTIBILITY TO DISINFECTANTS: L. pneumophila is susceptible to 1% solutions of sodium hypochlorite, 2% phenol, 2% gluteraldehyde, isopropyl alcohol, and formaldehyde(19).
PHYSICAL INACTIVATION: L. pneumophila can be inactivated in water by UV light, and temperatures of 80 °C for 0.4 minutes when in its aqueous environment.(20). Autoclave conditions of 121 °C for 15 minutes(21).
SURVIVAL OUTSIDE HOST: L. pneumophila is found naturally in most fresh water sources, including lakes, ponds, and rivers(1,12,13). It is also found in cooling towers, plumbing systems, water heaters, and warm water spas(3,7) L. pneumophila was found to survive for up to 139 days in distilled water and 415 days in tap water(22). Can persist outside of the host in biofilms like those formed in potable and health care facility water systems > 98 days(23). Clinical specimens will usually support the survival of L. pneumophila for up to 1 week(3).
SURVEILLANCE: Monitor for symptoms. Diagnosis can be confirmed via identification of L. pneumophila , often isolated from respiratory secretions, by culturing, immunofluorescent staining, urine antigen tests, PCR or serologic tests(3,24).
Note: All diagnostic methods are not necessarily available in all countries.
FIRST AID/TREATMENT: Respiratory fluoroquinolones and the newer macrolides are used to treat L. pneumophila pneumonia(1,13). Treatment typically lasts 7-10 days or in the case of immunosuppressed patients, 21 days(1). Pontiac fever usually does not require antimicrobial therapy.
PROPHYLAXIS: None, but prior antibiotic therapy may reduce the risk of acquiring pneumococcal L. pneumophila infection(18).
LABORATORY-ACQUIRED INFECTIONS: One case of a laboratory acquired infection with L. pneumophila has been reported(11). Infection was the result of aerosol inhalation during animal challenge studies.
SOURCES/SPECIMENS: Sources of L. pneumophila in the laboratory include expectorated sputum, lower respiratory specimens, pleural fluid, blood, pericardial fluid, kidney, liver, spleen, myocardium and soft tissues(3). Other sources include water samples from water systems and fresh water sources(1,13,23).
PRIMARY HAZARDS: Inhalation of aerosols during manipulation of infection samples or cultures is the primary hazard associated with L. pneumophila(11) .
SPECIAL HAZARDS: Franscisella tularensis and L. pneumophila can both be grown on buffered charcoal yeast extract media, which along with a cross reaction in serotyping experiments has led to the misidentification of F. tularensis as L. pnuemophila.(3)
CONTAINMENT REQUIREMENTS: Containment Level 2 facilities, equipment, and operational practices for work involving infectious or potentially infectious materials, animals, or cultures.
PROTECTIVE CLOTHING: Lab coat. Gloves when direct skin contact with infected materials or animals is unavoidable. Eye protection must be used where there is a known or potential risk of exposure to splashes(27).
OTHER PRECAUTIONS: All procedures that may produce aerosols, or involve high concentrations or large volumes should be conducted in a biological safety cabinet (BSC). The use of needles, syringes, and other sharp objects should be strictly limited. Additional precautions should be considered with work involving animals or large scale activities(27).
SPILLS: Allow all aerosols to settle and, while wearing protective clothing, cover the spill gently with paper towel and apply appropriate disinfectant solution starting at the edges of the spill zone and working inward. Allow an appropriate contact time clean up(27).
DISPOSAL: Decontamination using steam sterilization, chemical disinfection, or incineration must be performed before disposal of infectious waste(27).
STORAGE: All infectious materials should be stored in sealed containers bearing the appropriate labeling(27).
REGULATORY INFORMATION: The import, transport, and use of pathogens in Canada is regulated under many regulatory bodies, including the Public Health Agency of Canada, Health Canada, Canadian Food Inspection Agency, Environment Canada, and Transport Canada. Users are responsible for ensuring they are compliant with all relevant acts, regulations, guidelines, and standards.
UPDATED: September 2010
PREPARED BY: Pathogen Regulation Directorate, Public Health Agency of Canada.
Although the information, opinions and recommendations contained in this Pathogen Safety Data Sheet are compiled from sources believed to be reliable, we accept no responsibility for the accuracy, sufficiency, or reliability or for any loss or injury resulting from the use of the information. Newly discovered hazards are frequent and this information may not be completely up to date.
Public Health Agency of Canada, 2010