Salmonella, weather and climate change in Australia

Global temperatures have increased over the previous century, due in large part to human actions. Changes in climate and increases in the variability and distribution of weather patterns are expected to have both direct and indirect consequences on human health. The incidence and distribution of infectious diseases in Australia is expected to shift as a result of increasing temperatures and shifts in precipitation and relative humidity patterns. Previous research has demonstrated a relationship between Salmonella infection and weather. This thesis investigates this relationship at a level of detail that has not previously been explored. This thesis uses local, daily data to explore the relationship between weather and Salmonella infection across Australia. Using notified cases of Salmonella infection from the national surveillance authority, and transformed weather station data from 1991 to 2004, a positive relationship between increasing temperatures and Salmonella infection, and a variable influence of changes in precipitation and humidity in Australia are determined at a level of detail previously unexplored. These relationships are demonstrated to vary across the climate regions of Australia with a 16% to 77% increase in the rate of Salmonella infection estimated for an increase in the average temperature from 15{u00B0}C to 20 {u00B0}C. The most positive influence of increasing temperatures on Salmonella infection is modelled in the tropical, warm humid regions of northern Australia. There is also variation in the relationship between infection and weather evident in the analysis of specific serovars (Salmonella Typhimurium in northern Australia and Salmonella Mississippi in Tasmania). These results suggest both regional variation and serovar specific variation in the transmission pathways of Salmonella susceptible to the influence of weather. These estimations present a baseline against which to estimate the success of future public health interventions, but they are susceptible to the ability and willingness of global populations to curtail future greenhouse gas emissions to levels estimated to produce only a 1 {u00B0}C to 2 {u00B0}C increase in global temperatures. The predictive ability of these regional and serovar-specific models of infection are validated using weather and notification data from 2005 2007 and then the modelled relationship between infection and weather is extrapolated to estimate the future incidence of Salmonella infection under a future (moderate) climate change scenario. Expected changes in temperature, relative humidity and population distribution in Australia are used to project a 1.5% increase in the incidence of Salmonella infection across all Australia by 2020, and a 2.8% increase in incidence by 2030. These projections correspond to an additional 9,400 cases of Salmonella infection in the community by 2020 and an additional 16,400 cases by 2030, with the largest proportional increase in disease estimated for the tropical humid northern regions of Australia