The ancients : Salmonella, Tuberculosis and Influenza

Abstract

Infections with Tuberculosis (TB), Influenza and Salmonellosis continue to pose significant challenges to public health and result in considerable work for public health agencies. The core aspects of my thesis outline four projects undertaken at the Victorian Government Department of Health (DH) and the Victorian Infectious Diseases Reference Laboratory (VIDRL) to fulfil the core requirements of the Masters of Philosophy in Applied Epidemiology (MAE) program. First, I present a cluster investigation of Salmonella Typhimurium 44 (S. Typhimurium 44) that was ongoing for more than six months and associated with three point source outbreaks, including one where it was possible to perform a cohort study. Investigation findings suggest an association with consumption of eggs, based on epidemiological and microbiological evidence obtained in two outbreaks. The first isolated S. Typhimurium 44 from tartare sauce made from raw eggs and eggs sampled from the source farm, and the second found an association with scrambled eggs in the cohort study. My second project used retrospective analysis of TB surveillance data from 2009 to 2011 to measure health system delay for TB in Victoria (that is, the interval between first health presentation for TB symptoms and treatment initiation), identify the factors associated with delay using logistic regression and explore the reasons behind delay using electronic case notes review. I found the median health system delay to be 31 days for all TB cases, 20 days for pulmonary TB (PTB) and 12 days for sputum smear positive PTB. Multivariable regression analysis found longer delay in females, older adults and extra-PTB sites and shorter delay in positive microscopy or nucleic acid testing. A wide range of reasons were identified, the most common being multiple visits to a General Practitioner. For my third project, I evaluated the TB surveillance system in Victoria using a mixed methods study design incorporating documents review, data analysis and key informant interviews. Overall, I found the TB surveillance system to be a complex but well-functioning system that is sensitive, flexible, widely accepted by stakeholders and produced good quality data. The key recommendations were to improve documentation on the system, improve feedback to stakeholders and increase the use of surveillance data to inform service provision and monitoring and evaluation activities. In addition, I also analysed the surveillance data to examine the epidemiology of TB in Victoria from 1993 to 2012. My fourth project adapted and field tested a new method for deriving influenza thresholds developed by the World Health Organisation (WHO) to calculate thresholds for two routine influenza-like-illness (ILI) datasets, laboratory data and hospital admissions for influenza using data from 2002 to 2011. I found that thresholds were easily derived using the WHO method and the new thresholds were used to revise the current ones used by the Victorian Sentinel General Practice Surveillance System. Finally, my thesis also lists the additional activities undertaken at both placements to capture the breadth of my MAE experience. These activities and projects supported the work of both placements and contributed to evidence base and informing policy and practice. Show more