Synonym: Pontiac fever
In 1976 there was a serious outbreak of pulmonary infection at a convention of the American Legion in Philadelphia who were meeting to commemorate the American 200th anniversary of independence. The causative organism was Legionella pneumophila. Pontiac fever was named after an outbreak in Pontiac, Michigan in 1968. It was caused by the same organism but it did not affect the lungs.
Most cases of Legionnaires' disease (LD), are caused by L. pneumophila, but there are many other species of the organism and mild illnesses, other than pneumonia, may be caused by these organisms. Legionella spp. are aerobic, Gram-negative bacilli. Serogroup 1 is the commonest cause of disease, but 18 serogroups are known. Other than L. pneumophila, 34 species of legionella have been identified, mostly from immunocompromised patients with pneumonia.
L. pneumophila is found in natural water supplies and soil. It is also found in many recirculating and water supply systems. The risk of infection has prompted guidance on the the precautions required to minimise this risk. This guidance can be found in the Approved Code of Practice (ACOP) for Legionnaires' disease on the Health and Safety Executive website.
- The Health Protection Agency (HPA) data is derived from laboratory confirmed reports and follow up questionnaires that collect information on whether the case is community, hospital acquired or travel associated.
- LD is an uncommon form of pneumonia. The disease has no particular clinical features that clearly distinguish it from other types of pneumonia, and laboratory investigations must therefore be carried out in order to obtain a diagnosis. Epidemiological definitions are given in the table below.
- Between 1980 and 2001 the HPA received reports of between 150 and 250 cases a year but since 2002 cases of LD have exceeded 300. In 2006 there were over 500 cases, reducing to 359 cases in 2008. From these figures it can be derived that:
- It is 2 to 5 times more common in men.
- The death rate is about 10 to 15%.
- 40 to 50% of all cases are related to travel, usually abroad.
- These numbers are an underestimate because of failure to diagnose and hence report less severe cases (CDC estimates that <10% of cases are reported).
- Older people are more likely to be infected and are more likely to die.
- Numbers are highest between June and September.
- The HPA give an epidemiological classification to clarify what their statistics refer to:
|Epidemiological definitions used by the Health Protection Agency|
|Legionnaires' Disease||Case Definitions|
|Confirmed cases*||Clinical or radiological evidence of pneumonia with a microbiological diagnosis by one of:
|Presumptive cases||Clinical or radiological evidence of pneumonia and a microbiological diagnosis of either:
|Hospital acquired cases||
|Travel associated cases||One or more overnight stays in holiday accommodation in the UK or abroad in the 2-10 days before onset of illness.|
|Travel associated clusters||Two or more cases who stayed at the same accommodation and with onset of illness within the same two years.|
|Community clusters||Two or more cases linked by area of residence or work, or places visited and sufficient proximity in dates of onset of illness to warrant further investigation**.|
|Community outbreaks||Community clusters for which there is strong epidemiological evidence of a common source of infection, with or without microbiological evidence, and in response to which control measures have been applied to suspected sources of infection.|
|*When submitted to the Specimen and Reference Microbiology Division, Respiratory and Systemic Infection Laboratory, all positive serum specimens are examined by the IFAT test in the presence of campylobacter blocking fluid, to eliminate cross reactions.
**This is a working definition: the decision to follow up cases is made locally.
- Add notes to any clinical page and create a reflective diary
- Automatically track and log every page you have viewed
- Print and export a summary to use in your appraisal
This organism lives naturally in water. It causes disease when water droplets containing the bacterium enter the atmosphere as fine particles or in an aerosol that enables them to be inhaled deep into the lungs. There they replicate and cause disease. Cooling towers are often a source of infection, as they produce a very fine aerosol. Spa baths, misting machines and showers have also been identified as sources of infection in the past. So too have air conditioning systems, especially if poorly maintained. The disease is not spread from person-to-person. 50% of Pontiac fever outbreaks have been linked to whirlpool spas or hot tubs.
These are all factors that impair immunity and include:
- Malignancy (particularly lung cancer and haematological malignancy)
- End stage chronic renal failure
- Advanced age
- Alcohol abuse
- Recent surgery
Two distinct clinical syndromes can be caused by different species, "pneumonic" and "non-pneumonic" (primarily Pontiac fever).
- Pneumonic - the more severe, Legionnaires' disease:
- The incubation period is usually 2-10 days.
- There is a prodrome for a day or two of mild headache and myalgia, followed by high fever, chills, and multiple rigors.
- 90% present with a cough that is usually unproductive at first but may progress to being productive.
- Up to a third may have dyspnoea, pleuritic chest pain and haemoptysis.
- There may be nausea, vomiting, diarrhoea and anorexia.
- Headache is common and the mental state may be impaired but focal signs are rare.
- Symptoms outside the chest predominate in the early stages but pulmonary symptoms predominate later.
- Has a higher attack rate in outbreaks.
- A shorter 1-2 days incubation period than the pneumonic form.
- The influenza-like illness with myalgia, fever, and headache is almost invariable. Only 50% having a cough.
- The disease is self-limiting.
- This similarity to other viral illnesses, coupled with an understandable lack of urgency in even seeking diagnosis, let alone the difficulties in actually achieving one, mean most cases and outbreaks are undiagnosed.
- Pyrexia and tachypnoea are common but for the level of temperature, there is a relative bradycardia in two thirds. This means that the pulse rate is not as high as would be expected for that level of temperature and not that it is slower than usual.
- There are no abnormalities in the upper respiratory tract but examination of the chest may show rales, rhonchi or consolidation.
- Rarer features include pericarditis, hepatomegaly and impaired mental state.
- It can be an issue deciding when and how to investigate community-acquired pneumonias (CAP). British Thoracic Society guidelines recommend investigations for legionella infection for all patients with severe CAP, for other patients with specific risk factors, and for all patients with CAP during outbreaks.
- For the purpose of confirmation of a case the HPA require one of the following:
- The Gold standard is isolation and culture of legionella species from clinical specimens, usually sputum - note: non-pneumophilic cases are almost universally culture negative.
- Seroconversion, meaning at least a four-fold increase in titre of indirect immunofluorescent antibody test (IFAT) incorporating a monovalent L. pneumophila serogroup 1 antigen by a validated technique.
- Confirmation of L. pneumophila urinary antigen using validated reagents or kits. Culture of sputum and serology have been the standard tests for many years but the development of urine testing gives faster results, improves the rate of correct diagnosis and because the result is swifter it allows earlier correct treatment resulting in a lower mortality.
- There are no commercial tests to confirm specific non-pneumophilic infections, and serological conversion rates are variable. The shift towards urine testing is likely to further limit detection of non-pneumophilic cases unless better tests for the full range of legionella species are developed.
- A presumptive case is where there is:
- a clinical diagnosis of pneumonia with a single high titre of 128 using IFAT or a single titre of 64 in an outbreak.
- A positive direct fluorescence (DFA) on a clinical specimen using validated monoclonal antibodies (also referred to as a positive result by Direct Immunofluoresence).
- Other investigations include:
- FBC that will show a leukocytosis and possibly disseminated intravascular coagulation.
- U&E and creatinine as there may be dehydration and occasionally inappropriate secretion of ADH produces hyponatraemia.
- Alkaline phosphatase may be low and along with abnormal LFTs this is an uncommon feature of pneumonia that may suggest the diagnosis.
- Blood gases in pneumonia.
- CXR is not specific but may show patchy consolidation and up to half may have pleural effusion. This may take 1 to 4 months to resolve
- With alteration in mental state lumbar puncture and CT of the brain may be required to exclude other causes. They are both normal in LD.
- Other causes of pneumonia, especially mycoplasma or viral.
- Left ventricular failure.
- Severe acute respiratory syndrome (SARS).
Legionnaires' disease must be in the differential diagnosis for any community-acquired pneumonia.
Useful investigations to diagnose atypical pneumonias
|Cause of pneumonia:||Mycoplasma pneumoniae||Legionella pneumophila||Chlamydophila (Chlamydia) pneumoniae|
|Blood tests||May be raised WCC or rarely evidence of haemolytic anaemia. ESR may be elevated. Serology titres and complement fixation tests/ELISA can help to confirm the diagnosis.||FBC may show left shift. Severe cases may have DIC evident on FBC/INR. Hyponatraemia may occur due to syndrome of inappropriate ADH secretion. Urea/creatinine can be raised if complicated by renal failure or dehydration. LFTs often non-specifically deranged. CK may be elevated in rhabdomyolysis. Serological tests on blood or urine may be used to confirm diagnosis.||Usually non-specific and unhelpful. Serology titres or polymerase chain reaction tests may be used to confirm the diagnosis.|
|CXR||Usually single lower-lobe bronchopneumonia pattern with lobar consolidation rare. Other possible patterns include atelectasis, nodular infiltration akin to TB/sarcoidosis, hilar adenopathy and rarely pleural effusion.||50% have pleural effusion. Patchy alveolar infiltrates may be seen. CXR can take up to 4 months to return to normal and may initially progress despite therapy.||Usually lower-lobe single subsegmental infiltrate. Pleural effusion found in up to a quarter of cases. Can progress to ARDS. CXR changes may take up to 3 months to resolve.|
- Pain and temperature may require drugs such as paracetamol, and oxygen is indicated if there is hypoxia.
- The antibiotic of choice is probably erythromycin although gastrointestinal upset from the disease and the tendency of this drug to do the same may make it less attractive. Doxycycline is an excellent alternative. Tetracycline, ciprofloxacin, other fluoroquinolone and macrolide drugs may be indicated. The course should be 10 to 21 days. In critically ill patients the newer macrolides and fluoquinones should be used as first line therapy.
Respiratory insufficiency, dehydration, multiple organ failure, acute renal failure.
About 10 to 15% die overall representing about 10% of those who are treated and not immunocompromised but rising to 80% in those who are untreated and immunocompromised. The death rate in nosocomial infection is around 50% but figures on death rates are very much complicated by other pathology. Early detection and treatment improves outcome.
- Travel associated Legionnaires' disease is linked to stays in holiday accommodation where intermittent use of facilities, variable temperatures and seasonal fluctuations of water flow may increase the risk of infection.
- Prevention needs to be a collaborative effort between health professionals, governments and the tourist industry and enormous progress has been made since EWGLI (European working group for legionella infections) began in 1986 to coordinate such activities in Europe - as a result a legionellosis surveillance network now connects 36 countries that report travel-associated cases to a computerised database in London.
- Travellers in the highest risk groups must seek medical attention as soon as possible if they suspect they might have Legionnaires' disease. The increasing number of whirlpool spas and hot tubs in hotels and cruise ships, and the difficulty in tracking outbreaks of Pontiac fever, emphasise the importance of adequate filtration and disinfection measures, coupled with strict application of bather capacity. If doctors are suspicious of chest infections acquired abroad then erythromycin or doxycycline are preferable to amoxicillin.
- Legionella species are ubiquitous in water supplies and the role of hospital water supplies in the spread of nosocomial infection is unclear. Water should be kept above 55?C and probably the bacterium should be sought, even in the absence of known infection, especially in places like transplant units where patients are very vulnerable.
- Public opinion about hospital-acquired infection is also creating pressure for a pro-active approach.
- Detection of outbreaks and detection of clusters is important and secondary preventive measures can then be undertaken.
Further reading & references
- Chest infections - adult, Clinical Knowledge Summaries (2007)
- Smeeks FC, Legionnaires Disease in Emergency Medicine, Medscape, Mar 2011
- Amanullah S, Posner D; Pneumonia, Atypical, Bacterial, eMedicine, May 2008.; Good radiology images and radiological overview.
- Evidence-based Guidelines for the Management of Community Acquired Pneumonia In Childhood. British Thoracic Society
- Legionnaires' disease, Health Protection Agency (various guidelines and dates)
- Health and Safety Executive; HSE website
- Guidelines for the management of community acquired pneumonia in adults, British Thoracic Society (2009)
- Den Boer JW, Yzerman EP; Diagnosis of Legionella infection in Legionnaires' disease. Eur J Clin Microbiol Infect Dis. 2004 Dec;23(12):871-8.
- File T et al; Guidelines for empiric antimicrobial prescribing in community-acquired pneumonia.; Chest 2004 May;125(5):1888-901.[abstract]
- Mills GD, Oehley MR, Arrol B; Effectiveness of beta lactam antibiotics compared with antibiotics active against atypical pathogens in non-severe community acquired pneumonia: meta-analysis. BMJ. 2005 Feb 26;330(7489):456. Epub 2005 Jan 31.
- Amsden GW; Treatment of Legionnaires' disease. Drugs. 2005;65(5):605-14.
- Roig J, Rello J; Legionnaires' disease: a rational approach to therapy. J Antimicrob Chemother. 2003 May;51(5):1119-29. Epub 2003 Mar 28.
- Lettinga KD, Verbon A, Weverling GJ, et al; Legionnaires' disease at a Dutch flower show: prognostic factors and impact of therapy. Emerg Infect Dis. 2002 Dec;8(12):1448-54.
- European Guidelines for Control and Prevention of Travel Associated Legionnaires' Disease, European Surveillance Scheme for Travel Associated Legionnaires' Disease and the European Working Group for Legionella Infections (2005)
- O'Neill E, Humphreys H; O'Neill E, Humphreys H; Surveillance of hospital water and primary prevention of nosocomial legionellosis: what is the evidence? J Hosp Infect. 2005 Apr;59(4):273-9.
- Stout JE, Yu VL; Hospital-acquired Legionnaires' disease: new developments. Curr Opin Infect Dis. 2003 Aug;16(4):337-41.
- Den Boer JW, Verhoef L, Bencini MA, et al; Outbreak detection and secondary prevention of Legionnaires' disease: a national approach. Int J Hyg Environ Health. 2007 Jan;210(1):1-7. Epub 2006 Sep 7.
|Original Author: Dr Richard Draper||Current Version: Dr Richard Draper|
|Last Checked: 25/08/2010||Document ID: 2379 Version: 26||© EMIS|
Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.