Applied Epidemiology in South Australia 2014 - 2015
Date
2015
Authors
Stewart, Jeffrey
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Abstract
The South Australian Communicable Disease Control Branch at SA
Health is responsible for public health and protection of South
Australians through the surveillance and detection of
communicable diseases. I was placed within the Branch between
2014 and 2015 as a Masters of Philosophy in Applied Epidemiology
(MAE) scholar. In this thesis I present work undertaken during my
placement to fulfil the requirements of the MAE.
Three of my projects all involved the investigation of Salmonella
Typhimurium phage type 9 (STM 9) notifications in South
Australia. Notifications of STM 9 have been increasing in South
Australia over the past ten years and in 2014 represent a third
of all Salmonella notifications in the state.
I conducted a data analysis of STM 9 notifications in South
Australia between 2005 and 2014. A descriptive and analytical
review of notifications was conducted to define trends and
changes in the surveillance data and to provide insight into the
increase in case numbers. The analysis compared sporadic and
outbreak cases and detailed the descriptive characteristics of
different multiple-locus variable-number tandem-repeat analysis
patterns reported for this phage type. The analysis identified
higher notification rates in people living in areas of higher
socio-economic advantage and a particular increase in case
numbers since 2012. It also identified a large proportion of
outbreaks associated with eggs.
I conducted a case control study to identify risk factors for
sporadic STM 9 notifications in South Australia. This project
involved interviewing sporadic STM 9 cases who were frequency
matched with controls by age category. The questionnaire explored
food, environmental and behavioural exposures. The interim
analysis included in this thesis includes 332 participants (40
participants short of the required sample size) and identifies
defrosting meat by submerging in water as a potential risk factor
and consuming caged eggs as a potential protective behaviour.
I investigated an outbreak of STM 9 in a group of school children
staying at a campsite in New South Wales while visiting Canberra
on a school excursion. The investigation was able to alert other
jurisdictions to the potential problem, which resulted in the
identification of another affected school group from New South
Wales. The cohort study with the South Australian school group
was unable to identify a specific source of the outbreak. The
environmental investigation conducted at the campsite did not
identify any problems and food and environmental samples obtained
were all negative for Salmonella.
For my remaining project I undertook an evaluation of the South
Australian infectious syphilis surveillance system. The
evaluation used the Centers for Disease Control and Prevention
guidelines to assess ten surveillance system attributes. The
impact of three proposed probable case definitions were also
assessed. I was able to identify that the system, although highly
sensitive, had variable data quality and inconsistencies due to
the lack of a systematically applied case definition.
Improvements in feedback to external stakeholders were
recommended. The probable case definition requiring single high
rapid plasma regain cut off greater than or equal to 16, and not
requiring a case to have risk factors, had the highest
sensitivity.
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Keywords
Blood Borne Viruses (BBV), Communicable Disease Control Branch, CDCB, Disease Surveillance and Investigation Section, DSIS, Master of Philosophy in Applied Epidemiology, MAE, Sexually Transmitted Infections, STI, Salmonella Typhimurium phage type 9, STM 9
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