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Emergency And Acute Medicine – Adult Fever
Basics Description
Fever is an elevation of core body temperature caused by an increase in the hypothalamic thermoregulatory set point. Prostaglandin E2 synthesis within the anterior hypothalamus mediates this process and is the primary target of antipyretic therapy. Normal core temperature is regulated around 37°C with circadian variation, typically lowest in the early morning and highest in the late afternoon. Fever must be distinguished from hyperthermia, in which temperature elevation occurs despite a normal hypothalamic set point, and from hyperpyrexia, defined as extreme temperatures above 41.5°C, often associated with central nervous system injury. Endogenous pyrogens such as interleukins and tumor necrosis factor, as well as exogenous pyrogens including bacterial endotoxins, raise the thermoregulatory set point. Patients receiving anticytokine agents or glucocorticoids may exhibit a blunted febrile response. Fever of unknown origin is defined as a temperature above 38.3°C for more than three weeks without an established diagnosis after appropriate evaluation.
Etiology
Fever may result from infectious processes involving the central nervous system, respiratory tract, gastrointestinal tract, genitourinary system, skin, soft tissue, bone, vascular structures, or cardiac endocardium. Noninfectious causes include neoplastic disease, drug reactions, toxidromes, hypersensitivity reactions, systemic inflammatory and rheumatologic disorders, endocrine abnormalities such as hyperthyroidism or pheochromocytoma, withdrawal syndromes, and miscellaneous conditions including pulmonary embolism and hemolytic anemia. Common causes of fever of unknown origin include occult infections such as tuberculosis or abscesses, malignancies such as lymphoma or renal cell carcinoma, and inflammatory disorders.
Diagnosis Signs And Symptoms
Patients may report chills, rigors, weight loss, or night sweats, which can suggest bacteremia, malignancy, or chronic infection. Certain fever patterns provide diagnostic clues, including relapsing, remittent, intermittent, or double quotidian fevers. High-risk features include immunosuppression, anticytokine therapy, incomplete vaccination status, intravenous drug use, pregnancy, recent chemotherapy, recent travel, and splenectomy. Physical examination should focus on accurate core temperature measurement, assessment for diaphoresis, heart rate response relative to temperature, mental status changes, muscle rigidity or clonus, and skin findings such as rash or petechiae. Signs of endocrine disease, including goiter or exophthalmos, should also be assessed.
Essential Workup
Rectal temperature measurement provides the most accurate assessment of core temperature. A thorough history and physical examination guide the need for further diagnostic testing, including evaluation of recent infections, travel, medication use, occupational exposures, animal or tick contact, and immunization history.
Diagnosis Tests And Interpretation
Laboratory evaluation may include a complete blood count to assess for neutropenia, leukocytosis, or atypical lymphocytosis. Serum lactate is useful for identifying sepsis and guiding resuscitation. Urinalysis, urine culture, and blood cultures should be obtained in systemically ill patients or those at risk for bacteremia. Additional testing such as malaria smears, stool studies, heterophile antibody testing, or inflammatory markers may be indicated based on clinical context. Imaging studies such as chest radiography are useful in patients with respiratory findings or unclear fever sources, while advanced imaging is reserved for suspected deep or focal infections.
Treatment
Prehospital care focuses on monitoring and stabilization in unstable patients. Initial emergency department management prioritizes airway, breathing, and circulation in critically ill individuals. Early administration of broad-spectrum antibiotics is indicated in patients with suspected sepsis, neutropenia, or other high-risk features. Antipyretics such as acetaminophen or nonsteroidal anti-inflammatory drugs may be administered for comfort. Empiric antimicrobial therapy should be tailored to patient risk factors, including coverage for neutropenic, asplenic, or immunocompromised patients. External cooling measures are rarely required.
Follow Up Disposition
Patients with unstable vital signs or severe illness require hospital or intensive care admission. High-risk populations, including neutropenic, immunocompromised, asplenic, elderly, or intravenous drug–using patients, warrant a lower threshold for admission even in the absence of a clear source. Stable, immunocompetent patients with an identified benign source or suspected viral illness may be discharged with appropriate follow-up. Referral is guided by the suspected underlying etiology.
Key Clinical Insights And Common Errors
Early identification of sepsis using lactate screening and prompt initiation of broad-spectrum antibiotics are critical. Clinicians should maintain a broad differential diagnosis and carefully evaluate immunosuppressed, elderly, and high-risk patients, as fever may be the only manifestation of serious disease. Failure to recognize atypical presentations or delayed treatment in vulnerable populations can lead to significant morbidity and mortality.
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