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Legionnaire's disease in elderly people: the first sign of an outbreak in community?


Community-acquired pneumonia results in approximately one in every thousand of the adult population being hospitalized each year [1]. Studies in the last decade have estimated that 0.5-5% of community-acquired pneumonia is due to infection with Legionella[2, 3]. Many of these infections are thought to be sporadic, but outbreaks continue to occur despite well-published guidelines on the eradication of the organism from potential aerosol-generating equipment[4, 5]. The majority (approximately 70%) of infections are diagnosed in patients over 50 years of age and therefore physicians caring for elderly People are not infrequently likely to have Legionella-infected patients under their care. This paper describes the recognition of a community outbreak affecting primarily elderly people, its investigation and clinical findings and discusses the features which should alert a clinician to consider legionnaires' disease.

The Outbreak

On 14 September 1990 an 85-year-old Chorley resident who had been hospitalized with pneumonia was confirmed as suffering from legionnaires' disease by serological testing. Initial enquiries revealed that he first fell ill on 3 September and in the ten days prior to this he had remained in the vicinity of his home except for two or three visits to local carpet showrooms. Further investigation revealed two aerosol-generating sources within a 300 metre radius of the patient's home. These, as well as water samples from the patient's home and the sites he had visited, were examined for Legionella organism with negative results. On 26 October 1990, a second patient also a resident of Chorley) was identified as suffering from legionnaires' disease. He also had not travelled outside the area in the ten days prior to the onset of his illness and it was noted that he lived only two streets away from the previous patient.

Measures to Control the Outbreak

As a result of these findings an outbreak control group was convened and hospital doctors and general practitioners were informed about the outbreak to aid in the early diagnosis of any further cases. Using the international criteria for defining a case of Legionella infection[5], a case-finding study was organized which reviewed all admissions of Chorley residents with lower respiratory tract infections to three local hospitals in the month preceding the onset of illness in the first patient. These patients were visited to elicit a history of their recent movements as well as to collect blood samples for Legionella serology. All new admissions from the Chorley area with lower respiratory tract infection were investigated for Legionella infection and antibiotic therapy to cover possible Legionella infection in these patients was instituted. Local environmental health officers visited industrial and commercial properties, offices and public buildings in the Chorley District to ascertain the presence of aerosol-generating equipment or cooling towers.


Case search: A further nine cases of Legionella infection were recognized. The ages, dates of onset and serological findings of the 11 patients are shown in Table I. Nine of the confirmed cases lived in Chorley and the other two worked in the town. All 11 patients with confirmed legionnaires' disease had significant contact with the town centre in the period before their illness and none had travelled outside the town. No patient died.
Table I. Serological findings in 11 cases of Legionella infection

                           1st specimen   Subsequent specimen(*)
Patient   (years)   Date of onset   RMAT   IFAT   RMAT   IFAT

 1          85         3. 9.91       256    256   >256   >512
 2          65          8.10.91       <8    <16    256     64
 3          85         19.10.91       <8    <16   >512   >512
 4          67         18.10.91       <8    <16   >512    128
 5          62         24.10.91       64     64   >512   >512
 6          49         21.10.91       <8    <16     16     64
 7          83         27.10.91       <8    <16     32     64
 8          82         16.10.91       <8    <16     32     64
 9          65         14.11.91       32     32   >512   >512
10          72         13.11.91       <8    <16    128     64
11          55         23.10.91       16     16     16     64

Clinical findings: The clinical features of the 11 cases are summarized in Table II. The following two case histories are typical and illustrate features which have been particularly associated with Legionella infection. The first case was an 85-year-old man who presented with a dry cough, fever, falls and urinary incontinence of two days' duration. He was a smoker, had not been abroad, nor did he keep any pets. On examination he was confused with a pyrexia of 38[degrees]C, a pulse of 90/min and a mitral regurgitation murmur. He had poor air entry into the chest with bilateral basal crepitations but no hepatosplenomegaly nor any neurological deficit.
Table II. Clinical features of the 11 cases

Common presenting symptoms
  Cough                                           5
  Falls                                           4
  Headache and myalgia                            3
  Altered mental state                            3
  Rigors                                          2
  Diarrhoea and nausea                            2

Common physical signs
  Pyrexia                                        11
  Chest signs                                    11
  Rigors                                          6
  Bradycardia relative to elevated temperature    3
  Hypotension                                     2

  Consolidation on chest radiograph              11
  Progression of abnormalities                    4
  Abnormal liver function                         8
  Proteinuria and miroscopic haematuria           8
  Anamia                                          3
  Hyponatraemia                                   2
  Hypophosphataemia                              Nil

Risk factors

  Advanced age {over 70 years                     5
                60-69 years                       4
  Cigarette smoking over 10/day                   5
  Chronic pulmonary disease                       2
  Alcohol consumption                             2
  Immunosuppression                              Nil
  Previous surgery                               Nil
  Organ transplant                               Nil

His initial investigations showed Hb: 13.8 g/dl, WBC: 13.8 x 10[sup.9]/l, ESR: 88 mm/h, sodium 127 mmol/l, potassium: 3.5 mmol/l, urea: 5.3 mmol/l, serum bilirubin: 31 mmol/l, alkaline phosphatase: 165 units/l, AST: 118 units/l, gamma GT: 20 units/l. Urine testing: protein + + +, blood + +. Cardiomegaly was seen on the chest radiograph with bilaterial lung shadowing. Sputum and blood specimens were cultured with negative results. Despite intravrnous cefotaxime, physiotherapy and rehydration he failed to respond.

The diagnosis of legionnaires' disease was entertained in view of his hyponatraemia, failure to produce purulent sputum and continuing pyrexia with rigors. A change to erythromycin produced a dramatic improvement within 48 hours.

A second patient was a 62-year-old man who had a 5-day history of myalgia and pyrexia with rigors. He was a non-smoker and also had not been abroad and did not keep any pets. On admission he had a pyrexia of 38.5[degrees]C with evidence of consolidation in the right lung base which was confirmrd by the chest radiograph. other investigations were performed with the following results: Hb: 14 g/dl, WBC: 11.8 x 10[sup.9]/1, sodium: 133 mmol/l, urea: 26.2 mmol/l, serum bilirubin: 23 [micro]mol/l, alkaline phosphatase: 85 units/l, AST: 421 units/l, gamma GT: 13 units/l. Sputum and blood were cultured with negative results. He failed to improve despite intravenous ampicillin for 48 hours and became more confused with signs of consolidation on the opposite side. Changing the antibiotic to erythromycin resulted in a sustained improvement.

Laboratory investigation: All suspected cases had at least two serum samples collected for Legionelia serology. An immunofluorescent antibody test (IFAT) detecting polyclonal immunoglobin to serogroups 1 to 6 of Legionella pneumophila and to L. micdadei and L. dumoffi was used in conjunction with a rapid micro-agglutination test (RMAT) to L. pneumophila serogroup 1[6, 7]. Cases were diagnosed as positive if the IFAT test showed a four-fold or greater rise in titre. Positive samples were then re-tested to differentiate specific IgM and IgG responses. The serological findings of the confirmed cases are shown in Table I. Legionella pneumophila was not isolated from any patient.

Environmental studies: Altogether, 225 premises were visited and water samples were collected from possible sources. A small cooling-tower was found within the town centre and was suspected to be the source of the outbreak. Investigations showed that it had been inadequately maintained and no records of regular disinfection or biocide dosing were available. However, no Legionella organisms were isolated from the unit and this is most probably attributable to the tower having been cleaned and disinfected before samples were obtained. It is significant that no further cases were recorded following adequate treatment of the cooling unit.


The differentiation of legionnaires' disease from other forms of community-acquired pneumonia on the basis of symptomatology and clinical findings is usually not possible although a history of travel within the previous two weeks or known exposure to an aerosol would heighten a physician's suspicions. Various features including hyponatraemia, abnormal liver function tests, gastrointestinal disturbances and altered mental state along with a presisting high pyrexia and chest signs have, if present together, been proposed as indicators of Legionella infection[8]. These findings are nearly always present in the more severely ill patients but in this incident many of the affected patients did not demonstrate all these features. Although right patients had abnormal liver function only two were hyponatraemic or had gastrointestinal disturbances-not uncommon in elderly patients-and none showed hypophosphataemia. Reliance therefore cannot be placed upon a group of signs and symptoms.

As was demonstrated in this outbreak, the failure to respond to antibiotic therapy should prompt consideration of Legionella infection. The penicillins and cephalosporins have little, if any, antibacterial effect on Legionella and in the more, severely affected patient erythromycin if given orally may only produce limited resolution of the illness. Intravenous therapy with erythromycin or the newer macrolides, combined with rifampicin or ciprofloxacin should be instituted in the patient with significant respiratory distress[9, 10].

All patients in this outbreak had abnormal chest radiographs on admission. We found that the extent of radiological infiltration did not correlate well with the severity of the clinical syndrome. In four patients radiographic abnormalities progressed despite appropriate treatment and, similarly, radiographic improvement often lagged behind clinical response, a feature previously reported[11].

In this incident the diagnosis of legionnaires' disease was confirmed or made retrospectively by serological tests. Because seroconversion seldom occurs earlier than 8 days after onset it does not provide a reliable means of early diagnosis in many acutely ill patients[12]. Rapid diagnosis can be achieved by detection of the antigen in urine or bronchial secretions but is available only in specialized laboratories[13]. However, culture of sputum and bronchial secretions should be undertaken as isolation may be achieved in 72 hours, and is available in most district laboratories. Legionella organisms were not isolated from sputum samples submitted from any of our patients probably because they were collected late in the illness or after appropriate antibiotic therapy. The failure to isolate Legionella from the suspect cooling-tower was almost certainly due to the unit being cleaned and disinfected before it was sampled. Although not all those eventually found to be infected were elderly, it was the presentation of the disease amongst older patients and the recognition that the first two cases were geographically linked which prompted the early recognition of this outbreak.

Although much advice has been given on the methods to control the multiplication of Legionella in cooling-systems, sporadic infections still occur among persons living in their vicinity[14]. The susceptible older person may be the first victim to indicate that control efforts have been inadequate and physicians caring for elderly people should not forget Legionella as a cause of community-acquired pneumonia.


[1.] Woodhead MA, MacFarlane JT, McCracken JS, Rose DH, Finch RG. Pneumonia in the community: incidence, radiology and outcome. Thorax 1986;41:714. [2.] Research Committee of the British Thoracic Society and the Public Health Laboratory Service. Community acquired pneumonia in adults in British hospitals 1982-83: a survey of aetiology, mortality, prognostic factors and outcome. Q Y Med 1987;239:195-220. [3.] Woodhead MA, MacFarlane JT, McCracken JS, Rose DH, Finch RG. Prospective study of the aetiology and outcome of pneumonia in the community. Lancet 1987;i:1446-9. [4.] Health and Safety Executive. Legionnaires' disease (Environmental Hygiene Series. Guidance Note No. 48). London: Her Majest's Stationary Officer, 1988. [5.] Memorandum. Epidemiology, prevention and control of legionellosis. Bull WHO 1990;68: 155-64. [6.] Harrison TG, Taylor AG. Diagnosis of Legionella pneumophila infections by means of formlised yolk sac antigens. F Clin Pathol 1982; 35:211-14. [7.] Harrison TG, Taylor AG. A rapid microagglutination test for the diagnosis of Legionella pneumophila (serogroup 1) infection. F Clin Pathol 1982;35:1028-31. [8.] MacFarlane JT. Legionnaires' disease. Practitioner 1983;227:1707-18. [9.] MacFarlane JT. Treatment of lower respiratory infections. Lancet 1987;ii:1446-9. [10.] Winter JH, McCartney C, Bingham J, Telfer M, White LO, Fallon RJ. Ciprofloxacin in the treatment of severe legionnaires' disease. Rev Infect Dis 1988;10(S1):218-19. [11.] Bartlett CLR, Macrae AD, MacFarlane JT. Legionelia infections. London: Edward Arnold, 1986;42-4. [12.] Monforte R, Estruch R, Vidal J, Cervera R, Urbano-Marquez A. Delayed seroconversion, legionnaires' disease and age. Lancet 1989;ii:1190. [13.] Birtles RJ, Harrison TG, Samuel D, Taylor AG. Evaluation of urinary antigen ELISA for diagnosing Legionella pneumophila serogroup 1 infection. F Clin Pathol 1990;43:685-90. [14.] Bhopal RS, Fallon RJ. Variation in time and space of non-outbreak Legionnaires' disease in Scotland. Epidemiol Infect 1991;106:46-61.
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Author:Peiris, V.; Prasad, M.K.D.~; Bradley, D.; Zawistowicz, W.; Sivayoham, S.; Naqvi, S.N.H.; Hutchinson,
Publication:Age and Ageing
Date:Nov 1, 1992
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