Strains of bacteria have evolved that are resistant to multiple antibiotic drugs and these cause infections that are difficult to treat. People and animals suffering from such infections are likely to be more severely ill, and for longer periods of time, than those infected with bacteria that are not resistant to these antibiotics. This study will compare human cases infected with resistant bacteria with a population of healthy controls in order to investigate the sources of multidrug-resistant bacteria within our communities, with a focus on the roles played by family pets in spreading infection between people. This study will provide important information for designing the best public health interventions to minimise the spread of multidrug-resistant bacteria within households and the wider community and thereby contribute to keeping people healthy. Further, the findings could potentially be applied to other close-contact infectious diseases.