The epidemiology of Q fever in Queensland, Australia and effectiveness of vaccination for prevention

Abstract

Q fever, caused by the small obligate intracellular, gram-negative pathogenic bacterium Coxiella burnetii, is primarily an occupationally-acquired zoonotic disease most commonly reported in people working in the livestock and meat industries who have direct or indirect contact with infected animals. The main preventive tool for Q fever is a vaccine (Q-VAX ® , Seqirus, Australia) that is recognised to be highly effective and providing long lasting protection. Its implementation requires pre-vaccination screening tests using serology and skin tests conducted in parallel. This is because the vaccine has more side effects in persons who have already had the disease Q fever, so testing for prior immunity is necessary before vaccination to avoid unwanted vaccine side effects. However, outbreaks of Q fever continue to be recorded in abattoirs and Q fever continues to be an important public health issue in Australia. The incidence of Q fever remains high especially in Queensland and New South Wales (NSW) though there is good evidence of improved Q fever control as a result of the implementation of the Q fever vaccination program. There is evidence that the Q fever vaccination has not been fully implemented because of the high incidence of Q fever among individuals targeted by past vaccination program.Therefore, this PhD thesis was mainly intended to assess the overall effectiveness of the Q fever vaccination program, and the associated Q fever notification and hospital admission rates, and the most risky exposures for the occurrence of Q fever in Queensland, Australia. Chapter 1 presents a literature review on Q fever at global and Australia levels. In chapter 2, I conducted a systematic review and meta-analysis on the seroprevalence of Q fever. Chapter 3 addresses estimation of vaccine failure rate and duration of immunity for Q fever using Cox proportional hazard model. I then explicitly addressed the accuracy of the Q fever pre-screening test using Bayesian latent class analysis in chapter 4. In chapter 5, I assessed the demographic and vaccination status factors associated with the incidence of Q fever infection using a case control design. In chapter 6, I modelled the rate of Q fever notification and hospitalization, and identified the associated factors using Poisson and Negative Binomial regression models. In chapter 7, I conducted a risk assessment using the enhanced Q fever exposure surveillance data using multiple correspondence analysis (MCA) technique. Finally, chapter eight highlight key findings, discuss them, and summarize the thesis.In summary, the results presented in this Thesis, address the knowledge gap regarding the incidence of Q fever in vaccinated individuals and the duration of immunity of the Q fever vaccine and the accuracy of the prescreening tests thereby addressing the overall effectiveness of the Q fever vaccination program and the resulting Q fever notification and admission rates in the Queensland. It presents evidence of the protective effect of being vaccinated using the Q fever vaccine...