Fever and Infection Screening

Fever is a regulated rise in body temperature driven by the host response to infection, inflammation, or other insults, and it is one of the most common reasons patients present to acute care. Screening the febrile patient at the front door means deciding, before a diagnosis is known, who may have a serious infection or sepsis and who can safely follow a less urgent pathway.

Definition

The recognition of elevated body temperature as a marker of the host response and the structured front-door assessment used to identify acutely ill patients who may have a serious infection or sepsis before a definitive diagnosis is established.

Scope

This topic covers the physiology of fever as a host response, the interpretation of fever within undifferentiated acute presentations, and the screening logic used to flag possible serious infection and sepsis at triage. It treats fever and infection screening as a reference topic in acute assessment; it is not a protocol for diagnosing or treating any individual febrile patient.

Core questions

• What does fever represent physiologically, and why does it accompany so many acute illnesses?
• How is a febrile presentation distinguished as low- versus high-risk before a diagnosis is known?
• How are infection and organ dysfunction recognised within front-door screening?

Key concepts

• Fever as a regulated host response
• Pyrogens and the hypothalamic set point
• Febrile undifferentiated presentation
• Sepsis recognition
• Organ dysfunction screening
• Source of infection

Mechanisms

Fever is an actively regulated elevation of the hypothalamic temperature set point, driven by pyrogens released during infection and inflammation rather than a passive overheating. The resulting rise in temperature is part of a broader host response that, when dysregulated in the setting of infection, can progress to sepsis — defined in current consensus as life-threatening organ dysfunction caused by a dysregulated host response to infection. Because fever itself is non-specific, front-door screening pairs temperature with other physiological signals and clinical context to estimate the probability and severity of underlying infection.

Clinical relevance

How febrile patients are screened at triage shapes which presentations are escalated for urgent assessment and which follow standard pathways. This entry describes the physiology of fever and the logic of infection screening as a reference topic; it does not provide thresholds, antimicrobial guidance, or treatment recommendations for any individual patient.

Epidemiology

Fever and febrile illness account for a substantial share of emergency and primary acute-care visits across all age groups, and most are self-limiting; the screening challenge is to identify the minority with serious bacterial infection or evolving sepsis. The redefinition of sepsis in 2016 reshaped how clinicians conceptualise the severe end of this spectrum.

Evidence & guidelines

Consensus definitions such as Sepsis-3 frame how infection-related organ dysfunction is recognised, and reviews of fever pathophysiology inform interpretation of the febrile response. Aggregate physiological scores validated for deterioration contribute to how febrile patients are stratified within front-door assessment. Much of the supporting literature is consensus- and review-based rather than trial-derived.

History

Fever has been recognised as a sign of illness since antiquity, but its modern understanding as a cytokine-mediated, actively regulated host response developed through twentieth-century work on pyrogens. The framing of severe infection evolved from the systemic inflammatory response syndrome of the 1990s to the organ-dysfunction-centred Sepsis-3 definition in 2016, changing how febrile severity is conceptualised at the front door.

Debates

How should serious infection be screened for when fever is non-specific?

Fever alone poorly distinguishes serious from self-limiting illness, so screening must combine temperature with other physiological and clinical signals; which combination best identifies sepsis at the front door remains an active question reshaped by the Sepsis-3 framework.

Key figures

• Mervyn Singer
• Edward Walter

Seminal works

• walter-2016
• singer-2016

Frequently asked questions

Is fever itself harmful?

Fever is primarily a regulated component of the host response rather than a disease in itself; its significance in acute care comes mainly from what it signals about a possible underlying infection or inflammatory process, which is why screening focuses on identifying the cause and severity.

Why can't fever alone tell whether an illness is serious?

Fever is non-specific and accompanies many self-limiting illnesses, so front-door screening combines temperature with other physiological signals and clinical context to estimate the probability of serious infection or sepsis.