The risk factors associated with<unk>  are not well known. However, it has been suggested that children under 5 years of age are more susceptible to<unk>  since they lack serum bactericidal activity against the infection. Older children and adults have much higher titers of bactericidal antibodies, which serve as a protective measure. Also children residing in warmer geographic areas have been associated with a higher risk of<unk>  infection.
Brazilian purpuric fever
Barcoo fever
Scarlet fever
Murine typhus
Boutonneuse fever
Spondweni fever
Boston exanthem disease
Adult-onset Still's disease