Finfer et al (2004) – population level incidence of severe sepsis, but only for patients admitted to the ICU (Australia and New Zealand)

Angus et al (2001) – population level incidence of severe sepsis, defined by ICD 9 coding of infection and organ dysfunction

Real figure lies somewhere in between – and may be higher now due to increasing age of population (with increasing co-morbidities)  and thus increasing risk of sepsis.