South Wales legionnaires’ disease outbreak declared over

12 October 2010, Public Health Wales

The Outbreak Control Team investigating cases of legionnaires’ disease in the Heads of the Valleys area has declared the outbreak over.
 

The last person with legionnaires’ disease linked to the outbreak area fell ill on 10 September and there have been no new cases since that date.
 
The Outbreak Control Team, comprising Public Health Wales, the Health and Safety Executive (HSE) and environmental health officers from eight South Wales local authorities, will be producing a report on the outbreak.
 
Dr Gwen Lowe, Consultant in Communicable Disease Control for Public Health Wales and Chair of the Outbreak Control Team, said: “We have not seen any new cases of legionnaires’ disease linked to the outbreak area for more than a month and we have extensively investigated all possible links between the 22 cases linked to the outbreak area.
 
“Both our microbiological and epidemiological investigations indicate that there are a number of potential sources for these 22 cases.
 
“All plausible sources have been fully investigated and precautionary action taken and advice given where indicated. This has involved the HSE and local authorities from all over South East Wales.”
 
Cases of Legionnaires’ Disease
 
  • 22 people with legionnaires’ disease were identified as being linked to the outbreak.
 
 
  • None of the 22 cases became unwell later than 10 September.
  • All 22 cases required hospital treatment. Two people have died, a 49 year-old female who died in hospital on Sunday 12 September and an 85-year-old male who died in hospital on Saturday 11 September.
  • Ten further people with legionnaires’ disease were investigated to see if they were linked to the outbreak but were excluded from outbreak investigations. Two of these patients died – a 70-year-old male and a 64-year-old female.
  • The outbreak area was the corridor 12km either side of the Heads of the Valleys Road (A465) between Abergavenny and Llandarcy. People were linked to the outbreak if they lived in, or visited, this area in the two weeks before they fell ill.
  • Epidemiological investigations identified two distinct clusters - six people with legionnaires linked to a small geographical area in Rhymney, and six people with legionnaires spread out across a wider area in the Cynon Valley. One case was counted twice as it had links to both clusters.
  • One further case resided within 5km of the Rhymney cluster, and has been considered as linked to this cluster.
  • Ten cases were not linked to either cluster but resided in, or visited, the outbreak area. 
  • One mini cluster of two cases was closely linked to a retail premises outside the outbreak area, and one mini cluster of three consisted of cases living in the Merthyr Tydfil area.
  • One further case was microbiologically confirmed as linked to a premises outside the outbreak area.
  • In the remaining four cases, no plausible explanation of their source was found.  These cases are believed to be sporadic cases of illness of the kind seen all year round across the country, in which a definitive source is rarely identified.
 
Dr Gwen Lowe said: “Growing legionella bacteria is very difficult and has not been possible in samples from many of the cases. Microbiological results from the seven human samples that have been grown show that every one is genetically distinct, suggesting a different source of infection for each of these seven cases. We have not been able to obtain samples for most of the cases in the two main clusters.
 
“This strengthens our suspicions that we are dealing with several different unlinked clusters and cases and is why we have not identified any outbreak strain of legionella for any cluster.
 
“For the whole outbreak area, plausible sources have been systematically inspected and where indicated, sampled. Cooling towers from industrial processes are classically linked to the type of legionella outbreaks where cases are closely clustered in time and place, as is the case with our two main clusters.
 
“However, the Outbreak Control Team has considered, sampled and ruled out a number of other plausible sources for these clusters.
 
“Investigation and sampling of cooling towers and industrial processes in the outbreak area has identified four located close to clusters where temporary closure, precautionary action and or further sampling have been undertaken, either on a voluntary basis or by Prohibition Notice. No live legionella bacteria have been grown from any of these premises and all are now back in operation.
 
“This has been an extremely complex outbreak investigation. We do not know why we have seen so many people with legionella during August and September, and why there have been so many different clusters of the disease in the same time period. Whilst some of the increased numbers of cases may reflect increased awareness and testing by doctors, the rise in the disease predates this increased awareness. We have not seen this increase in other parts of Wales.
 
“A detailed report of the outbreak will be prepared and published after it has been ended and after legal proceedings, if any, are completed.”
 
Outbreak investigations
 
  • The Health and Safety Executive (HSE) inspected all registered cooling towers and evaporative condensers in the Merthyr Tydfil, Blaenau Gwent, Rhondda Cynon Taff and Rhymney area, to assess the operation and safety of systems that have the potential to proliferate legionella.  In total, 28 registered premises were visited.
  • A Prohibition Notice was served by the HSE at a site in Dowlais, Merthyr Tydfil.  The notice was served as the cooling towers were not being operated in accordance with the Approved Code of Practice (ACOP) on “The control of Legionella bacteria in water systems” issued by HSE. The Prohibition Notice resulted in the cooling tower and site being immediately shut down until the tower was thoroughly cleaned and disinfected in accordance with the ACOP.  The cooling tower has since been cleaned and disinfected and therefore the notice has been complied with and the company is able to restart work.
  • HSE inspections of cooling towers and other sites resulted in nine Improvement Notices being served at six different sites requiring companies to further improve the operation of their systems.
  • Following contact by environmental health officers, a company in the Rhymney Valley voluntarily closed its cooling tower in order for it to be disinfected. This precautionary action followed preliminary microbiological results on samples taken from the cooling tower which made it possible that legionella bacteria was there. No live legionella was grown following microbiological testing. Following disinfection, the company was advised that it could reopen.
  • A second company in the Rhymney Valley voluntarily shut down a wet scrubber as a precaution on the evening of 11 September.  The way in which the premises was operating was considered low risk.  Following sampling, the company was advised that it could reopen.
  • Following contact by environmental health officers, a company in the Cynon Valley voluntarily closed its cooling tower in order for it to be disinfected. This precautionary action followed preliminary microbiological results on samples taken from the cooling tower which made it possible that legionella bacteria was there. No live legionella was grown following microbiological testing. Following disinfection, the company was advised that it could reopen.
  • None of the four sites were definitively identified as the source of the outbreak from sampling.
  • Another three premises with cooling towers and/or evaporative condensers that were not registered with the appropriate local authority were identified and visited. 
  • Any action taken by HSE has been to ensure that all cooling towers and evaporative condensers in these areas are well managed and any potential risks controlled.
  • In addition, local authority environmental health officers ensured that samples were taken from a number of sites to try and identify whether the legionella bacterium was present.
  • HSE and local authority environmental health officers (from all authorities involved) also visited more than 100 other workplaces in the area as a further means of attempting to identify the source. 
  • Information was gathered on the people with the disease to identify where they had been at times when they may have caught the infection.
  • The Outbreak Control Team gathered meterological data for the areas affected.
  • Experts in London carried out specialist typing of samples from patients and premises to determine whether they could be matched.
  • A team of more than 100 staff from 10 agencies were involved in outbreak investigations.
 
For more information on Legionnaires’ disease visit:  http://www.wales.nhs.uk/sitesplus/888/legionnaires-disease
 
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