Legionnaires' disease outbreak investigation toolbox

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Legionnaires' disease background

Legionnaires' disease is an atypical form of pneumonia caused by bacteria of the genus Legionella [1; 2; 3]. The majority of cases are reported as single (sporadic) cases which can occur throughout the year, with most cases occuring in late summer early and autumn [3; 4; 5]. Clusters (cases associated in space and time) and outbreaks (cases associated in space and time with a common source) can also occur [6; 7; 8; 9]. A large proportion of cases are travel-associated, acquired on holidays or business trips abroad [3; 5]. This is possibly due to differing reporting or diagnosis practice between member states and can cause particular challenges in source identification. All ages can be affected, but the disease mainly affects people over 50 years of age, and generally men more than women [4; 10]. Smokers, the immuno-compromised, people with certain occupations, and people with underlying medical conditions may be at a higher risk of infection [1].

The early symptoms of Legionnaires' disease can include a 'flu-like' illness with muscle aches, tiredness, headaches, dry cough and fever [1; 2]. The fatality rate of Legionnaires' disease can vary from 1-17% of cases from the general population and may be higher in some groups of patients, as mentioned above [6; 7; 8; 9; 11]. The incubation period averages 6 days. Legionnaires' disease can also cause long-term sequelae such as restrictive pulmonary disease, weakness and fatigue and neurological problems.

Susceptible persons become infected when they inhale Legionella bacteria which have been released into the air in aerosolised form from a contaminated source. Once in the lungs, the bacteria multiply and can cause pneumonia. Infection via aspiration can occur, although rarely, especially for nosocomial patients. There is no evidence of person-to-person transmission [12]. Legionella organisms are found widely in the environment; they have been found in ponds, in hot and cold water systems and water in air conditioning cooling systems. There are more than 50 recognised species of legionellae (for more detail visit the DSMZ website) and at least 19 of these are associated with human infection, one of which, Legionella pneumophila, causes around 80-90% of all infections. L. pneumophila serogroup 1 is the most common cause of illness.

Other associated infections

Pontiac fever

Pontiac fever presents as a mild, self-limiting, illness characterised by fever and influenza-like symptoms without pneumonia and is rarely fatal [13]. It differs epidemiologically from Legionnaires' disease in that it has a short incubation period (typically 12 - 48 hours) and a high attack rate (70 - 90%). The disease often affects previously healthy and young individuals, with cases having a median age of 29 years [13]. Pontiac fever cases are often found in conjunction with Legionnaires' disease outbreaks [14; 15; 16; 17; 18].

Non-pneumonic Legionnaires' disease

Occasionally, L. pneumophila urinary antigen-positive cases are detected which do not fit the definition of Pontiac fever and have no evidence of any pneumonia. Such cases are considered non-pneumonic cases of Legionnaires' disease, and these occur rarely.

Reference List

  1. FIELDS B. S., BENSON R. F. & BESSER R. E. (2002) Legionella and Legionnaires' disease: 25 years of investigation Clinical Microbiology Reviews 15(3) pp.506 - 526 http
  2. STOUT J. E. & YU V.L. (1997) Legionellosis The New England Journal of Medicine 337, pp.682 - 687 http
  3. BARTRAM J. (2007) Legionella and the prevention of legionellosis WHO, Geneva ISBN 92 4 156297 http pdf
  4. AMATO-GAUCI A., AMMON A. (2009) Annual epidemiological report on communicable diseases in Europe 2009 European Centre for Disease Prevention and Control, Revised Edition, June 2010 http pdf
  5. HPA (2010) (Health Protection Agency UK) Legionnaires' Disease http://www.hpa.org.uk/Topics/InfectiousDiseases/InfectionsAZ/LegionnairesDisease/. http
  6. DEN BOER J. W, YZERMAN P. F.E., SCHELLEKENS J., LETTINGA K. D, BOSHUIZEN H. C, VAN STEENBERGEN J. E, BOSMAN A., VAN DEN HOF S., VAN VLIET H. A, PEETERS M. F., VAN KETEL R. J., SPEELMAN P., KOOL J.L., & CONYN VAN SPAENDONCK M. A. E. (2002) A large outbreak of Legionnaires' disease at a flower show, the Netherlands, 1999 Emerging Infectious Diseases 8(1), pp.37-43 http pdf
  7. GREIG J. E., CARNIE J. A., TALLIS G. F., RYAN N. J., TAN A. G., GORDON I. R., ZWOLAK B., LEYDON J. A., GUEST C. S. & HART W. G. (2004) An outbreak of Legionnaires' disease at the Melbourne Aquarium, April 2000: investigation and case-control studies The Medical Journal of Australia. 180(11), pp.566-572. http
  8. NGUYEN T. M. N., ILEF D., JARRAUD S., ROUIL L., CAMPESE C., CHE D., HAEGHEBAERT S., GANIAYRE F., MARCEL F., ETIENNE J. & DESENCLOS J.C. (2006) A community-wide outbreak of Legionnaires' disease linked to industrial cooling towers: How far can contaminated aerosols spread? Journal of Infectious Diseases 193, pp.102-111 http
  9. NYGARD K., WERNER-JOHANSEN O., RONSEN S., CAUGANT D. A., SIMONSEN O., KANESTROM A., ASK E., RINGSTAD J., ODEGARD R., JENSEN T., KROGH T., HOIBY E. A., RAGNHILDSTVEIT E., AABERGE I. S. & AAVITSLAND P. (2008) An outbreak of Legionnaires' disease caused by long-distance spread from an industrial air scrubber in Sarpsborg, Norway Clinical Infectious Diseases 46(1), pp.61-69 http
  10. BENIN A. L., BENSON R. F. & BESSER R. E. (2002b) Trends in Legionnaires' disease, 1980-1998: declining mortality and new patterns of diagnosis Clinical Infectious Diseases 35, pp.1039 - 46 http
  11. GARCIA-FULGUEIRAS A., NAVARRO C., FENOLL D., GARCIA J., GONZALEZ-DIEGO P., JIMENEZ-BUNUALES T., RODRIGUEZ M., LOPEZ R., PACHECO F., RUIZ J., SEGOVIA M., BALADRON B. & PELAZ C. (2003) Legionnaires' disease outbreak in Murcia, Spain Emerging Infectious Diseases 9(8), pp.915 - 921 http pdf
  12. RICKETTS K. D., CHARLETT A., GELB D., LANE C., LEE J. V. & JOSEPH C. A. (2008) Weather patterns and Legionnaires' disease: a meteorological study Epidemiology and Infection 19, pp.1 -10 http
  13. TOSSA P., DELOGE-ABARKAN M., ZMIROU-NAVIER D., HARTEMANN P. & MATHIEU L. (2006) Pontiac fever: an operational definition for epidemiological studies BMC Public Health 6, 112 http pdf
  14. BENIN A.L., BENSON R.F., ARNOLD K.E., FIORE A.E., COOK P.G., WILLIAMS L.K., FIELDS B., BESSER R.E. (2002) An outbreak of travel-associated Legionnaires' disease and Pontiac Fever: the need for enhanced surveillance of travel-associated legionellosis in the United States The Journal of Infectious Diseases 185, pp.237 - 43 http
  15. EUSER S. M., PELGRIM M. & DEN BOER J. W. (2010) Legionnaires' disease and Pontiac fever after using a private outdoor whirlpool spa Scandinavian Journal of Infectious Diseases 42(11-12), pp. 910-916. http
  16. FIELDS B.S., HAPUT T., DAVIS J.P., ARDUINO M.J., MILLER P.H. & BUTLER J.C. (2001) Pontiac fever due to Legionella micdadei from a whirlpool spa: possible role of bacterial endotoxin Journal of Infectious Diseases 184 (10), pp. 1289-1292. http
  17. JONES T. F., BENSON R. F., BROWN E. W., ROWLAND J. R., CROSIER S. C. & SCHAFFNER W. (2003) Epidemiologic investigation of a restaurant-associated outbreak of Pontiac fever Clinical Infectious Diseases 37, 1292 - 1297 http
  18. WARD M., BOLAND M., NICOLAY N., MURPHY H., MCELHINEY J., COLLINS C., LYNCH M., MCCARTHY M. & O' DONNELL J. (2010) A cluster of Legionnaires' disease and associated Pontiac Fever morbidity in office workers, Dublin, June-July 2008 Journal of Environmental and Public Health 2010, art. no. 463926, doi:10.1155/2010/463926 http pdf