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�Outbreak� of Legionnaire�s disease, Brisbane 2013
In late May and early June of this year, we were inundated with media coverage about the �outbreak� of Legionnaire�s disease in a Brisbane hospital, during which at least one person died. However, we haven�t heard much about these other �outbreaks�. From the website of HCInfo (http://www.hcinfo.com/) :
Footscray, Australia, Dec 2012
According to health officials, five people who contracted Legionnaires’ disease since December all passed through the central Footscray area. Footscray is near Melbourne. Three of the patients–aged 56, 69, and 93–have recovered and been discharged from the hospital. A 75-year-old woman was still in the hospital as of last Thursday. A man in his 50s, who had underlying medical conditions, died on January 24th. Health officials apparently focused their investigation on cooling towers, testing and disinfecting about two dozen in Footscray. http://www.health.vic.gov.au/chiefhealthofficer/alerts/alert-2013-01-legionnaires.htm
Melbourne, April 2013
The web site, http://www.theage.com.au, reported on April 22nd that the Victorian Department of Health linked four cases of Legionnaires’ disease to the Melbourne Airport. The cases occurred among people who had traveled through the airport sometime in March or April. Legionella was not found in the airport’s cooling towers. No other tests or possible Legionella sources were mentioned in the article.
South Australia, March 2013
Legionnaires’ disease has been diagnosed in three individuals who had been in the east part of Adelaide (South Australia) during the incubation period. Public health authorities asked business owners to disinfect cooling towers even though a common source had not been identified.
Auckland, New Zealand, 16 Cases, Feb-May 2012
Sixteen cases of Legionnaires’ disease have been identified in Auckland, New Zealand since late February. Two persons have died, both of whom had underlying illness. Because the outbreak was widely dispersed and the investigators had no obvious links, the Auckland Regional Public Health Service issued a press release asking operators of commercial and industrial buildings to shock dose cooling towers. More than 600 cooling towers were disinfected. A definite link between cooling towers and the outbreak has not been established.
At the time of writing (June) there has been much information disseminated in the press and other media about Legionnaires disease � some of it accurate, some not. It is timely to revisit some issues around this organism.
Assignment questions
1. Statistics on Legionnaires disease incidence.
What is/are the organism(s) responsible for this disease? What species are the most common?
What is the definition of an �outbreak�?
One media commentator was heard to say that �this disease does not occur in isolation�..� – is this true? What is the incidence of sporadic (endemic) cases vs outbreak (epidemic) cases? (you will need to consult national and state health departments for statistics)
Is there a subgroup of the population who are more susceptible? If so, who are they?
Why do you think the Brisbane outbreak received so much media attention? (What were the characteristics of this very small outbreak that made it media-worthy?)
2. Pathogenesis
Outline the main mechanisms of pathogenicity for these organisms. What is/are their predominant virulence factor(s) and how do they work? Why are some people more susceptible?
3. Ecology
Where in the environment are the organisms found? How do they survive (include a discussion of the role of biofilms)?
One of the media reports on the Brisbane outbreak reported a hospital spokesperson as saying – �They are dealing with an extraordinary situation because the situation hardly ever occurs in water systems.� Is this true?
There has been some speculation that reducing the temperature of hot water systems to 45-50oC to save on energy costs is allowing the organisms to grow � is this likely and what should a risk assessment and/or cost benefit analysis of this practice take into account?
Some years seem to be worse than others for incidence of Legionnaires disease. What might be the reasons for this variation?
4. Diagnosis
The pathology department involved in identifying the organisms from the Brisbane outbreak has been criticised for taking too long to identify the causative organisms and failing to report this to the health authorities in Queensland.
Outline diagnostic techniques that might be used to investigate an outbreak of Legionnaires disease and highlight the difficulties inherent in identifying this organism. Why might it take several days (or longer) for a diagnosis?
Whose responsibility is it to notify health departments of a case of Legionnaires disease (or any other notifiable disease)? Use SA legislation as a guide and consider that the hospital authorities in the Brisbane case were notified but did not themselves notify the Health Dept., and remembering that the hospital is a private health provider and not a public hospital.
Format of Assignment
Each section should be answered in an essay style but use of diagrams and dot points is allowed. A short introductory paragraph and a concluding statement are recommended to tie the sections together.
References (including any diagrams used) must be cited in text using the Harvard referencing system. The University has recently produced a guide to Harvard.
For a guide to how marks will be allocated see the feedback sheet at the end of these notes.
References/Resources
These references should be used only as a starting point, I expect to see more in your final assignment.
Microbiology:
Key components of this assignment:
Q1:
Detailed statistical analysis including appropriate figures. Derive your own graphs of incidence. Compare numbers for sporadic and endemic cases. Definitions of outbreak and susceptible population.
Q2:
Detailed discussion of pathogenesis including the major virulence factors and how they work.
Q3:
Detailed discussion of the ecology of Legionella including where they reside in the environment and how they come to infect humans. Describe the structure and production of biofilms and the role they play in legionellosis.
Q4:
Describe culture of the organism in the laboratory, speciation and strain typing methods and include time lines for this testing. Describe the notification process in South Australia.
Overall structure and referencing, and conclusions:
Includes clarity of written expression � spelling, grammar- logical progression, relevant, up-to-date information, evidence of further reading, correct use of references, etc.
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