Severe disseminated BCG infection is rare and often associated with severe abnormalities in host responses, most notably severe combined immunodeficiency (SCID) or chronic granulomatous disease (CGD). However, many patients have no defined immunodeficiency and often normal resistance to other pathogens and were regarded as having 'idiopathic disseminated BCG infection. Children with idiopathic disseminated infection due to enviromental non-tuberculous mycobacteria have also been reported. It has been reported that in less than half of these patients have associated salmonella infection. IFN-gamma R1, IFN-gamma R2, IL-12R beta1 and IL-12p40 deficiencies have been shown in some of these patients.