What causes fever with shivering in the absence of other influenza (flu) symptoms?

Fever with Shivering Without Flu Symptoms: Differential Diagnosis

When a patient presents with fever and shivering (rigors) but lacks typical respiratory symptoms like cough, sore throat, or rhinitis, you must immediately consider life-threatening bacterial infections, tick-borne diseases, and malaria before attributing symptoms to viral illness. 1

Immediate Life-Threatening Causes to Rule Out

Bacterial Sepsis and Bacteremia

• Adults with unexplained fever and rigors have a 35% likelihood of occult bacterial infection, with 44% of these having bacteremia. 2
• Risk is particularly elevated if the patient has: age ≥50 years, diabetes mellitus, white blood cell count ≥15,000/mm³, neutrophil band count ≥1,500/mm³, or erythrocyte sedimentation rate ≥30 mm/h. 2
• With 3 or more of these risk factors present, the probability of occult bacterial infection reaches 55%. 2

Tick-Borne Rickettsial Diseases

• The American College of Physicians recommends immediate empirical doxycycline 100 mg twice daily for any patient with fever and history of tick exposure or outdoor activities in rural/wooded areas, as delayed treatment can result in severe complications or death. 1
• The typical incubation period is 5-7 days after tick exposure. 1
• Critical pitfall: Do not exclude tick-borne disease based on absence of rash, as rash may appear late or be absent in a significant percentage of cases. 1
• Thrombocytopenia and leukopenia on complete blood count strongly suggest rickettsial disease. 1

Malaria

• Any travel history to malaria-endemic regions within the past 2-10 days to several months mandates immediate malaria evaluation with peripheral blood smear, as this is a medical emergency. 1
• Travel history is the single most important determinant in the evaluation. 1
• Elevated lactate dehydrogenase and creatinine kinase support the diagnosis. 1

Meningococcemia and Meningitis

• Examine the entire skin surface for petechial or purpuric rash, which suggests meningococcemia requiring immediate attention. 1
• Assess for neck stiffness, though the absence of Kernig and Brudzinski signs does not rule out meningitis due to their low sensitivity. 1

Common Focal Bacterial Infections

Urinary Tract Infections and Pyelonephritis

• The most frequent cause of intermittent fever with rigors is focal bacterial infection, particularly infections localized to the urinary tract. 3
• These can present with fever and shivering before localizing symptoms develop. 3

Biliary Tract Infections (Cholangitis/Cholecystitis)

• Infections of the biliary ducts commonly cause intermittent fever with rigors. 3
• May present before right upper quadrant pain or jaundice become apparent. 3

Colonic Infections and Diverticulitis

• Colonic infections represent another frequent cause of fever with shivering without initial localizing symptoms. 3

Infections of Foreign Material

• Infections associated with indwelling catheters, prosthetic joints, or other foreign bodies can present with isolated fever and rigors. 3

Less Common but Important Causes

Infective Endocarditis

• Can present with intermittent fever and rigors without obvious cardiac symptoms initially. 3
• Requires high index of suspicion in patients with known valvular disease or injection drug use. 3

Tuberculosis

• May present with fever and night sweats (which can be perceived as shivering) before respiratory symptoms develop. 3

Yersinia enterocolitica Infection

• Can cause fever without prominent gastrointestinal symptoms initially. 3

Diagnostic Approach

Essential Initial Laboratory Tests

• Complete blood count with differential to evaluate for thrombocytopenia, leukopenia, or leukocytosis. 1
• Complete metabolic panel to assess liver transaminases, renal function, and electrolytes, particularly sodium. 1
• Lactate dehydrogenase and creatinine kinase, which are elevated in malaria and rickettsial diseases. 1
• Blood cultures should be obtained before antibiotics if bacterial infection is suspected. 2

Physical Examination Priorities

• Examine the entire skin surface, including palms and soles, for any rash. 1
• Check for petechiae or purpura suggesting meningococcemia. 1
• Assess for neck stiffness, though its absence does not exclude meningitis. 1
• Evaluate for signs of toxicity: lethargy, poor perfusion, altered mental status. 4

Red Flags Requiring Immediate Hospitalization

• Any altered mental status, confusion, or seizures suggesting cerebral malaria, encephalitis, or severe rickettsial disease. 1
• Persistent hypotension (systolic BP <90 mmHg). 1
• Oxygen saturation <92% or respiratory distress. 1
• Petechial or purpuric rash. 1
• Severe neck stiffness. 1

Critical Clinical Pitfalls to Avoid

• Never assume a "non-toxic" appearance excludes serious bacterial infection—appearance is not predictive of occult bacterial infection. 2
• Never rely on fever height alone; temperature ≥39.4°C (103°F) is not predictive of occult bacterial infection. 2
• Never delay empirical doxycycline if clinical suspicion of rickettsiosis exists, especially with tick exposure history. 1
• Never ignore the possibility of co-infections, as ticks can transmit multiple pathogens simultaneously. 1
• Never assume brief outdoor exposure is insignificant for tick-borne illness. 1