Travel and weather implicated as secondary legionalla risk factors

Thirty years after the first known outbreak in Philadelphia in 1976, legionnaires’ disease remains a continuing problem for building occupiers.

In July this year, the Health and Safety Executive (HSE) renewed its warning to building and factory occupiers to ensure that water storage and cooling systems are adequately treated to prevent the growth of Legionella pneumophila bacteria. Poorly maintained water systems, the HSE said, continue to provide a source of infection that leads to approximately 300 people in the UK becoming hospitalised each year.

The HSE issued its warning after a court in Hereford fined Scottish and Newcastle cider producer Bulmers, and its water services consultant Nalco, £300,000 plus £50,000 costs each for breaches of the Health and Safety at Work Act associated with a legionnaires’ disease outbreak in 2003, as a result of which two people died1.

The Bulmers case underlined the fact that the occupier-consultant relationship remains critical to effective cooling tower maintenance, and that this work has to be regarded as a safety-critical, facilities management activity. As in Barrow-in-Furness in 2002 – where seven deaths resulted from the borough council’s failure to ensure that a suitable water treatment contractor was appointed – so in Hereford, the cider producer was shown to have made inadequate provision for water system maintenance: it had engaged a specialist contractor but had not ensured it was receiving the service required. “A problem passed to a consultant is not a problem solved,” the HSE said after the case. “The fact that building users engage a specialist contractor does not mean that they have complied with the law they must work with the contractor and ensure they are receiving the service required. Equally, specialist contractors and subcontractors must provide their clients with the expertise which they have been engaged for.”

Two of the company’s cooling towers, brought into seasonal autumn service without adequate cleaning, spread contaminated water vapour across Hereford town centre, resulting in 28 confirmed cases of legionnaires’ disease. The HSE investigation showed that the cleaning specification for the cooling towers drawn up by specialists Nalco was inadequate. For example, it failed to take account of the fact that, because the towers were only used for three months of the year, contamination could accumulate during down-time. The cleaning specification was not in line with the HSE’s statutory guidance document L8 Legionnaires’ disease: the control of Legionella bacteria in water systems and the company’s staff were “inadequately trained, inadequately briefed and inadequately supervised”, the HSE said. Both Bulmers and Nalco were found guilty of failing to protect the public, in breach of section 3(1) of the HSW Act.

The seriousness with which courts view the issue is reflected in the increasing level of fines being imposed for management failures. In 2004, a fine of £80,000, with £23,000 costs, was imposed following failings at the Royal United Hospital, Bath. In 2006, although Barrow Borough Council and one of its officials escaped manslaughter convictions following two trials, they were, respectively, fined £125,000 (plus £90,000 costs) and £15,000 (plus costs) for causing the UK’s biggest outbreak – with 170 confirmed and 498 suspected cases. The prosecution of Bulmers and Nalco led to record fines being imposed, despite the Hereford outbreak being on a smaller scale than Barrow.

Malfunctioning cooling towers behind most major outbreaks

Twenty years after the 1987 official inquiry into the 22-fatality outbreak at Stafford District General Hospital in 1985 identified a significant hazard in UK hospital cooling towers (and led to a series of recommendations for official guidance to be issued, towers to be registered, etc)2, poorly maintained cooling towers remain the main cause of legionnaires’ disease outbreaks in the UK. However, whereas at the time of the Stafford outbreak hospitals were the source of a significant number of outbreaks (including those at Churchill Hospital, Oxford and Kingston Hospital, Surrey), this is not the case today (although hospital-associated cases are more likely to lead to death, for obvious reasons).

Travel-related legionnaires’ disease cases

The HSE issued its warning about the public health hazard associated with legionnaires’ disease in its capacity as enforcer of the HSW Act, under which it has powers to tackle not only occupational health risks but also risks to public health, provided they are occupational in origin.

It should be noted, however, that the HSE’s reference to 300 people being affected by legionnaires’ disease annually in the UK as a result of poorly maintained water systems excludes cases that are not UK-occupational in origin. In fact, of the more than 450 cases of legionnaires’ disease recorded in residents of England and Wales last year, a third were likely to have been contracted as a result of spells spent in hotels, either in the UK or abroad.

Improved international surveillance of legionnaires’ disease infections has revealed the extent to which hotels can be sources of infection and allowed problem locations to be identified and remedial action taken. The surveillance is the result of an EU-sponsored collaboration between public health bodies in more than 30 European countries, known as the European Working Group for Legionella Infections (EWGLI), which operates a web-based network for the international surveillance of travel-associated legionnaires’ disease (EWGLINET).

As well as collating reports of travel-associated cases reported in collaborating countries, EWGLI coordinates outbreak investigations, develops standardised definitions and reporting methods, organises training and supervises a scheme whereby hotel operators are required to implement post-incident remedial measures or face “blacklisting” on the network’s website3.

In a recent paper4, epidemiologists working within the UK’s collaborating centre – the HPA’s Centre for Infections, which runs the EWGLINET scheme – presented an analysis of reports from more than 20 countries made to the scheme in 2006.

EWGLI guidelines on the prevention of travel-related legionnaires’ disease5, endorsed by the EU Commission in 2003, provide for consistent investigation of cases, and clusters of cases6, identified. When a traveller who has contracted legionnaires’ disease has stayed (during the two- to 10-day incubation period) at a hotel participating in the EWGLINET scheme, the hotel is sent a checklist to ensure it is following the best practice for control of risk of legionella contamination of its water systems. This is a precautionary measure as there may be no connection between the illness and the hotel. When a cluster is identified as being associated with a particular hotel, however, the guidelines require more detailed investigation, including a risk assessment, sampling and control measures. Progress with the investigation has to be reported and if these reports are incomplete or are not received on time, EWGLINET publishes details of the cluster site on its public website (, indicating that there is uncertainty about whether the risk of legionella infection is under control at the site.

In 2006, 124 new clusters of cases were identified through the scheme, leading to 111 site investigations being carried out. In 2006/07, four hotel locations (in Bulgaria, France, Poland and Turkey) were listed on the website for non-compliance with EWGLI requirements. One-third of these cases were only detected as a result of the operation of the EWGLINET reporting scheme.

Hot and humid weather raises risk level

The record number of cases of legionnaires’ disease that occurred in England and Wales in 20067 has been studied by Health Protection Agency specialists to test the hypothesis that meteorological conditions played a significant part, rather than the high number being either a chance event or the result of improved levels of detection. Five hundred and fifty‑two cases were recorded in 2006, compared with 354 the previous year, peaking in August when nearly twice as many cases were recorded compared with a year earlier. The level fell back again in 2007.

Data on cases suspected of being caused by point sources was examined without revealing any such causes. The most notable difference between the 2006 and previous years was that in 2006 the majority of infections (336) were classified as “community-acquired” – that is, they were acquired as a result of normal day-to-day activities with no apparent link with travel nor exposure to a known source of infection. This is consistent with the theory that the cause of the excess incidence was the summer 2006 weather: a period of high temperature early in the year followed by intense rain and high humidity, ideal conditions for legionella bacteria – first to multiply and grow, and secondly to be dispersed as an aerosol and remain suspended in the atmosphere for long periods.

Legionella control proficiency qualifications

Two new qualifications for occupational health and safety specialists responsible for water systems – including cooling towers, evaporative condensers, spa pools and hot water systems – have been introduced by the British Occupational Hygiene Society. P901 Legionella – management and control of building hot and cold water services and P902 Legionella – management and control of evaporative cooling and other high risk systems aim to provide background and an overview of the risk of legionella infection and how it can be controlled in these different types of water systems. The examination modules are usually taken after attendance at one of a number of training courses run by external course providers throughout the UK. Information on the modules and course providers is available from BOHS, tel: 01332 298101.


  1. “HSE prosecutes HP Bulmer Ltd and Nalco Ltd following outbreak of legionnaires’ disease”,

  2. Second report of the committee of inquiry into the outbreak of legionnaires’ disease in Stafford in April 1985 (the Badenoch report), HMSO 1987.

  3. European Working Group for Legionella Infections,

  4. Ricketts KD, Yadav R, and Joseph CA. “Travel‑associated legionnaires’ disease in Europe: 2006.” Euro Surveill. 2008 13(29): pii=18930. Available online:

  5. European guidelines for control and prevention of travel-associated legionnaires’ disease, available at:

  6. A cluster is defined as two or more people being infected who, within the same two-year period, stayed at the same hotel during the two- to 10-day period preceding their illness.

  7. “Causes of high levels of legionnaires’ disease under investigation”, OHR 132, March/April 2008, p.4.

From Occupational Health Review, September 2008

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