One-liner#

Evaluate acute fever (<7 days) in adults by identifying the source, distinguishing viral from bacterial infection, recognizing patients who need urgent intervention, and avoiding unnecessary antibiotics in self-limited viral illness.

Quick nav#

• Red flags / send to ED
• Key history
• Focused exam
• Differential (quick pattern recognition)
• Workup
• Initial management
• Management by diagnosis
• Follow-up
• Patient instructions
• Smartphrase snippets

Red flags / send to ED#

• Hemodynamic instability (SBP <90, HR >120, altered mental status) → sepsis; call 911
• Meningeal signs (neck stiffness, photophobia, severe headache) → ED for LP
• Petechial or purpuric rash → ED (meningococcemia, DIC)
• Severe respiratory distress (RR >30, SpO2 <92%, accessory muscle use) → ED
• Immunocompromised with fever (neutropenia, active chemo, transplant, high-dose steroids) → ED
• Severe abdominal pain with fever → ED (appendicitis, cholecystitis, perforation)
• Fever with new heart murmur → ED (endocarditis)
• Fever with joint swelling (single hot joint) → ED (septic arthritis)
• Fever in asplenic patient → ED (overwhelming post-splenectomy infection)
• Fever >104°F (40°C) with toxic appearance → ED

Urgent (same-day evaluation, not necessarily ED):

• Fever with dysuria in elderly or diabetic (complicated UTI/pyelonephritis)
• Fever with productive cough and focal lung findings (pneumonia)
• Fever with severe sore throat and trismus (peritonsillar abscess)
• Fever with facial swelling/erythema (facial cellulitis, dental abscess)

Key history#

Definition of fever:

• Temperature ≥100.4°F (38°C) is generally accepted threshold
• Elderly may not mount fever; lower threshold (>99°F or 1°F above baseline) may be significant
• Hypothermia with infection is a bad sign (sepsis)

Fever characteristics:

• Onset and duration
• Maximum temperature (documented vs subjective)
• Pattern (constant, intermittent, cyclic)
• Response to antipyretics
• Associated chills, rigors (rigors suggest bacteremia)

Localizing symptoms (ask systematically):

• Respiratory: Cough, sputum, dyspnea, sore throat, nasal congestion, sinus pain
• GI: Nausea, vomiting, diarrhea, abdominal pain
• GU: Dysuria, frequency, urgency, flank pain, vaginal/penile discharge
• Skin: Rash, wound, cellulitis, abscess
• MSK: Joint pain/swelling, back pain
• Neuro: Headache, neck stiffness, photophobia, confusion
• Cardiac: Chest pain, palpitations

Exposure history:

• Sick contacts (household, work, daycare)
• Recent travel (domestic and international)
• Animal exposures (pets, bites, ticks)
• Food exposures (undercooked meat, raw seafood, unpasteurized dairy)
• Water exposures (swimming, hot tubs)
• Sexual history (new partners, STI risk)
• Occupational exposures (healthcare, childcare, agriculture)

Medical history:

• Immunocompromising conditions (HIV, diabetes, cancer, transplant, autoimmune on immunosuppression)
• Chronic diseases (COPD, heart failure, CKD, liver disease)
• Recent surgery or procedures
• Indwelling devices (catheter, port, pacemaker, prosthetic joint/valve)
• Splenectomy
• Recent hospitalization
• Recent antibiotics (C. diff risk)

Medication review:

• Immunosuppressants (steroids, biologics, chemotherapy)
• Recent antibiotics
• Drug fever (antibiotics—especially beta-lactams, sulfonamides; anticonvulsants; allopurinol; typically 7-10 days after starting drug; patient often looks well despite fever)

Travel history (if recent international travel):

• Malaria (fever + travel to endemic area = malaria until proven otherwise; refer urgently)
• Dengue, chikungunya, Zika (mosquito-borne; rash, arthralgias)
• Typhoid (South Asia, Africa; GI symptoms)
• Traveler’s diarrhea with fever (bacterial gastroenteritis)
• Any fever within 3 months of travel to malaria-endemic area needs urgent evaluation

Vaccination status:

• Influenza (current season)
• COVID-19
• Pneumococcal
• Other relevant vaccines

Focused exam#

Vital signs (critical):

• Temperature (oral, tympanic, or temporal; rectal if concern for hypothermia)
• Heart rate (tachycardia out of proportion to fever = concerning)
• Blood pressure (hypotension = sepsis until proven otherwise)
• Respiratory rate (>20 concerning; >30 = severe)
• Oxygen saturation

General:

• Toxic vs non-toxic appearance
• Hydration status
• Mental status

HEENT:

• Conjunctivitis
• Sinus tenderness
• Pharynx (erythema, exudates, tonsillar enlargement, peritonsillar bulge)
• Oral lesions
• Lymphadenopathy (cervical, submandibular)
• Ear exam (TM erythema, bulging, effusion)

Neck:

• Meningismus (nuchal rigidity)
• Lymphadenopathy

Lungs:

• Breath sounds (crackles, rhonchi, wheezes, decreased breath sounds)
• Egophony, dullness to percussion (consolidation)

Cardiovascular:

• Murmurs (new murmur = endocarditis until proven otherwise)
• Tachycardia

Abdomen:

• Tenderness (localized vs diffuse)
• Guarding, rebound (peritonitis)
• CVA tenderness (pyelonephritis)
• Hepatosplenomegaly

Skin:

• Rash (type, distribution)
• Cellulitis
• Wounds
• Petechiae, purpura (medical emergency)
• IV sites, surgical sites

Musculoskeletal:

• Joint swelling, erythema, warmth
• Range of motion
• Back tenderness (epidural abscess, osteomyelitis)

Genitourinary (if indicated):

• Costovertebral angle tenderness
• Pelvic exam if PID suspected
• Testicular exam if epididymitis suspected

Differential (quick pattern recognition)#

Common/likely (outpatient)#

Can’t-miss / urgent#

Workup#

Most febrile patients do NOT need extensive workup. Let history and exam guide testing.

When NO workup needed:

• Classic viral URI with low-grade fever, no red flags, immunocompetent
• Influenza-like illness in flu season (may test to confirm)
• Mild gastroenteritis with clear exposure history

Basic workup (when source unclear or moderate illness):

When to get blood cultures:

• Suspected bacteremia or sepsis
• Endocarditis concern
• Immunocompromised with fever
• Fever with rigors
• Pyelonephritis requiring hospitalization
• Do NOT routinely obtain in uncomplicated infections

Procalcitonin:

• May help distinguish bacterial from viral infection
• <0.25 ng/mL suggests viral; >0.5 ng/mL suggests bacterial
• Most useful in respiratory infections and sepsis
• Not routinely needed in clear-cut cases

Initial management#

Supportive care (all patients):

• Antipyretics for comfort (fever itself is not harmful in most adults)
• Hydration
• Rest

Antipyretics:

Antibiotics: Only when bacterial infection confirmed or highly suspected.

Do NOT give antibiotics for:

• Viral URI
• Acute bronchitis (almost always viral)
• Viral pharyngitis
• Influenza (antivirals, not antibiotics)
• Uncomplicated viral gastroenteritis

Management by diagnosis#

Viral URI#

Education:

• Caused by viruses; antibiotics don’t help and can cause harm
• Symptoms typically last 7-10 days; cough may persist 2-3 weeks
• Contagious for first few days

Treatment:

• Supportive: rest, fluids, antipyretics
• Symptomatic relief: decongestants, antihistamines, honey for cough
• Saline nasal irrigation

Follow-up: Return if worsening after 7-10 days, high fever develops, or new symptoms.

Influenza#

Education:

• Flu is a serious viral infection; antivirals can shorten duration if started early
• Most contagious first 3-4 days
• High-risk patients need close monitoring

Treatment:

High-risk patients (treat even if >48h from onset):

• Age ≥65
• Chronic medical conditions (COPD, asthma, heart disease, diabetes, CKD, immunocompromised)
• Pregnancy
• BMI ≥40
• Nursing home residents

Follow-up: Return if worsening dyspnea, persistent high fever >3-4 days, or dehydration.

COVID-19#

Education:

• Isolate for 5 days; mask for 10 days
• Monitor for worsening (especially days 5-10)
• High-risk patients may benefit from antiviral treatment

Treatment (high-risk patients, within 5 days of symptom onset):

Paxlovid drug interactions (must hold or avoid):

• Statins (especially simvastatin, lovastatin)
• Certain anticoagulants (rivaroxaban—reduce dose; avoid with apixaban)
• Certain antiarrhythmics
• Colchicine
• Many others—check interaction checker

Follow-up: Return if worsening dyspnea, SpO2 <94%, persistent fever >4 days, or unable to stay hydrated.

Acute bacterial sinusitis#

Education:

• Most sinusitis is viral; antibiotics only help bacterial cases
• Bacterial sinusitis: symptoms >10 days OR severe symptoms OR “double-worsening”
• Antibiotics shorten duration by ~2 days

When to treat with antibiotics:

• Symptoms ≥10 days without improvement
• Severe symptoms (fever ≥102°F, severe facial pain) for ≥3-4 days
• “Double-worsening” (improving then worsening)

Treatment:

Follow-up: Return if no improvement in 3-5 days or worsening.

Streptococcal pharyngitis#

Education:

• Strep throat is bacterial and needs antibiotics to prevent complications
• Contagious until 24 hours on antibiotics
• Symptoms improve in 1-2 days on treatment

Centor criteria (1 point each):

• Tonsillar exudates
• Tender anterior cervical lymphadenopathy
• Fever (by history)
• Absence of cough

Testing approach:

• Centor 0-1: No testing, no antibiotics
• Centor 2-3: Rapid strep test; treat if positive
• Centor 4: Can treat empirically or test

Treatment:

Follow-up: Return if not improving in 48-72 hours or worsening (peritonsillar abscess signs).

Uncomplicated UTI (cystitis)#

Education:

• Bladder infection; very common in women
• Antibiotics work quickly; symptoms improve in 1-2 days
• Drink plenty of fluids

Treatment:

Follow-up: Return if symptoms persist >48 hours, fever develops, or flank pain.

Pyelonephritis#

Assess for complicated vs uncomplicated:

Uncomplicated (can treat outpatient):

• Young, healthy woman
• No vomiting (can take oral meds)
• No sepsis signs
• No urologic abnormalities

Complicated (consider hospitalization):

• Male
• Pregnancy
• Diabetes, immunocompromised
• Urologic abnormality (stones, obstruction, catheter)
• Sepsis signs
• Unable to tolerate oral intake

Outpatient treatment (uncomplicated):

Always obtain urine culture before starting antibiotics.

Follow-up: 48-72 hours to ensure improvement; adjust antibiotics based on culture.

Community-acquired pneumonia#

Assess severity (CURB-65):

• Confusion
• Urea >7 mmol/L (BUN >20)
• Respiratory rate ≥30
• BP <90 systolic or ≤60 diastolic
• Age ≥65

Score interpretation:

• 0-1: Outpatient treatment
• 2: Consider hospitalization
• 3+: Hospitalize (4-5: consider ICU)

Outpatient treatment (healthy, no comorbidities):

Outpatient treatment (comorbidities: COPD, diabetes, heart/liver/renal disease, immunocompromised, recent antibiotics):

Follow-up: 48-72 hours; CXR in 6-8 weeks if smoker or age >50 to ensure resolution.

Cellulitis#

Education:

• Skin infection; needs antibiotics
• Mark the borders to track spread
• Elevation helps
• May take 48-72 hours to see improvement

Assess for abscess: If fluctuant, needs I&D (incision and drainage).

Treatment (non-purulent cellulitis—strep coverage):

Treatment (purulent cellulitis/abscess—MRSA coverage):

Follow-up: 48-72 hours to ensure improvement; return sooner if spreading despite antibiotics.

Follow-up#

Viral illness:

• No routine follow-up needed
• Return if not improving in 7-10 days or worsening

Bacterial infection on antibiotics:

• 48-72 hours if not improving
• End of treatment if complicated infection

Return precautions (all patients):

• Fever >3-4 days without improvement
• New or worsening symptoms
• Difficulty breathing
• Unable to keep fluids down
• Confusion or altered mental status
• Rash (especially petechiae)
• Severe headache with neck stiffness

Patient instructions#

• Fever is your body’s way of fighting infection. Most fevers are caused by viruses and get better on their own.
• Rest and drink plenty of fluids. Water, broth, and electrolyte drinks are good choices.
• You can take acetaminophen (Tylenol) or ibuprofen (Advil/Motrin) for comfort, but you don’t have to treat the fever if you’re feeling okay.
• Antibiotics only work for bacterial infections. Taking them for a virus won’t help and can cause side effects.
• If you were prescribed antibiotics, take the full course even if you feel better.
• Wash your hands frequently and cover coughs/sneezes to avoid spreading infection.
• Call or return if: fever lasts more than 3-4 days, you’re getting worse instead of better, you have trouble breathing, you can’t keep fluids down, you develop a rash, or you feel confused.

Smartphrase snippets#

.FEVERVIRALURI Acute febrile illness consistent with viral upper respiratory infection. Symptoms include [rhinorrhea, sore throat, cough, low-grade fever] for [X days]. No red flags. Exam: [findings]. Viral URI does not require antibiotics. Supportive care recommended: rest, fluids, antipyretics PRN. Return if symptoms worsen, fever persists >3-4 days, or new symptoms develop.

.FEVERFLU Influenza-like illness. Abrupt onset fever, myalgias, cough, [other symptoms]. [Rapid flu positive/clinical diagnosis during flu season]. [Starting oseltamivir 75 mg BID x 5 days / Supportive care as low-risk patient]. Isolation recommended. Return precautions: worsening dyspnea, persistent high fever, dehydration.

.FEVERBACTERIAL Acute fever with [source: UTI/sinusitis/pharyngitis/cellulitis/pneumonia]. [Relevant history and exam findings]. [Workup results]. Starting [antibiotic, dose, duration]. Expect improvement in 48-72 hours. Return if no improvement, worsening symptoms, or new concerns. [Follow-up plan].

.FEVERSEPSIS Concern for sepsis given fever with [hypotension/tachycardia/altered mental status/tachypnea]. Patient appears [toxic/ill]. Activating emergency response. [IV access attempted / 911 called]. Patient being sent to ED for further evaluation and management.

Coding/billing notes#

• R50.9: Fever, unspecified
• J06.9: Acute upper respiratory infection, unspecified
• J11.1: Influenza with other respiratory manifestations
• U07.1: COVID-19
• J01.90: Acute sinusitis, unspecified
• J02.9: Acute pharyngitis, unspecified
• J02.0: Streptococcal pharyngitis
• N30.00: Acute cystitis without hematuria
• N10: Acute pyelonephritis
• J18.9: Pneumonia, unspecified organism
• L03.90: Cellulitis, unspecified