SIRS develops from systemic spill over of what often starts as a localised inflammatory and coagulation response to a known inflammatory stimulus. Aetiology can be infectious or non-infectious. Infectious causes can include infection caused by bacteria, viruses and yeasts.

A good knowledge of local infection patterns is vital and it is important that the microbiology department are involved at an early stage.

Gram positive cocci and gram negative bacilli are the most commonly implicated in the pathogenesis of sepsis. Atypical bacteria should also be considered.