What are the definitions of sepsis, severe sepsis, and septic shock?

Infection is the invasion of a normally sterile tissue by microorganisms.
Bacteremia is the presence of viable bacteria in the blood.
SIRS is the clinical syndrome resulting from a dysregulated inflammatory response to a non-infectious trigger.
Severe sepsis is defined as sepsis with evidence of organ dysfunction, hypoperfusion, or hypotension.
Septic shock is defined as hypotension induced by sepsis that persists despite adequate fluid resuscitation and is accompanied by hypoperfusion and/or organ dysfunction.