Host response to infection

Overview

The host inflammatory/immune response to infection - fever, acute phase reactant production, and the coordinated innate/adaptive immune cascade - is usually protective, but an excessive or dysregulated response (as in sepsis) can itself cause organ dysfunction independent of direct pathogen effects
Relevant to essentially every infectious presentation, since clinical severity often reflects the host response magnitude as much as the pathogen's intrinsic virulence

Pathogen recognition (via pattern recognition receptors detecting conserved microbial molecular patterns) triggers cytokine release, fever (via hypothalamic prostaglandin-mediated set-point elevation), and acute phase protein production (CRP, and altered iron handling reducing pathogen iron availability) - a coordinated response that is protective in appropriate magnitude but becomes pathological when dysregulated/excessive, as in the systemic inflammatory response underlying sepsis and septic shock

Inflammatory markers (CRP, white cell count, and in severe presentations, lactate as a marker of tissue hypoperfusion) provide an indirect window into host response magnitude, complementing direct pathogen identification
Recognising when the host response itself (rather than ongoing uncontrolled infection) is driving clinical deterioration is relevant to management decisions, though this distinction can be difficult in practice

Sepsis represents a dysregulated host response causing organ dysfunction, and its management (per the 2026 Surviving Sepsis Campaign guidelines) emphasises early recognition, source control, and appropriate antimicrobial therapy alongside haemodynamic support to address both the infection and the host response consequences
Fever management (antipyretics) treats patient comfort rather than the underlying infection, and fever suppression does not need to be a primary treatment goal in most infections

Sepsis/septic shock (host response dysregulation as the defining feature), cytokine storm phenomena, acute phase reactant kinetics, fever as an adaptive (not solely pathological) response

Fever itself is generally an adaptive host response (impairing pathogen replication and supporting immune function) rather than purely a harmful symptom - routine aggressive antipyretic treatment aimed at normalising temperature is not required for most infections and treats patient comfort rather than a physiological problem needing correction

5 more sections, plus exam facts

Premium unlocks every note across every specialty, and the full exam fact library behind it.