Week 3 - Bloodstream Infections

Bacteremia definition

The presence of bacteria in the blood - may have no disease implications

Septicemia definition

The presence of bacteria in the blood with clinical symptoms

Sepsis

Systemic inflammatory response (SIRS) plus infection - documented or suspected

Severe sepsis

Sepsis induced organ dysfunction or tissue hypo-perfusion

Septic shock

Sepsis induced hypotension not responding to fluid resuscitation

Causes of sepsis

• Bacteria and their products

• Fungi - yeasts and filamentous fungi

• Some systemic and localized viral infection (canine parvo, influenza, ebola)

• Malaria

Sepsis - bacteria in blood

• Interaction between cells of the innate immune system of the host and the infecting organism

• A localized infection may proceed to bacteria entering the bloodstream causing clinical symptoms

Sepsis - no bacteria in blood, bacterial components in blood

• A localized infection releases bacterial components into the blood causing clinical symptoms

• There are no live bacteria in the blood

Bacterial components in blood

• Gram neg bacteria & products (endotoxin)

• Gram pos bacteria & products (peptidoglycan)

Toxins (superantigens) in blood

• Certain bacterial toxins called superantigens cause the systemic symptoms of shock

• Bacteria involved in skin or soft tissue infection release these toxins which have systemic effects

How do host cells recognize foreign invaders?

• Recognize conserved molecule present on many pathogens: Pathogen-associated molecular patterns (PAMPs) & NB - present on non-pathogens

• Recognize essential component - little opportunity to vary

• Bacterial molecules that have these characteristics: Lipid A (LPS), Peptidoglycan, Bacterial DNA, Bacterial lipoproteins

Severe sepsis/septic shock clinical complications

• Acute respiratory distress syndrome (ARDS)

• Cardiac output initially rises then falls

• Hypotension often leads to renal failure

• Hematology: incr white cells, decr platelets

• DIC: disseminated intravascular coagulation

• Widespread tissue ischemia & organ failure

• Increased bleeding

Therapy to treat sepsis

• "Goal directed therapy"

• Maintenance of physiological parameters as close to normal as possible

• Fluid management

• Respiratory support

• Renal support

• Antimicrobial chemotherapy within 1 hr of diagnosis

Viral infections

• Primary viraemia

• Secondary viraemia

• Viral infections of blood and tissue may cause the clinical signs of sepsis