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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 influenzalike 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 longdistance 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 travelassociated 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