Influenza symptoms without fever
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Influenza Symptoms Without Fever: Clinical Presentation and Diagnostic Challenges
Common Influenza Symptoms Beyond Fever
While fever is a well-known symptom of influenza, many people experience other symptoms even in the absence of fever. The most common symptoms of influenza, with or without fever, include cough, sore throat, nasal congestion, runny nose (rhinorrhea), headache, muscle aches (myalgia), malaise, chills, and fatigue. These symptoms can occur alone or in combination, and their presence can still indicate influenza, especially during flu season 245.
Prevalence and Predictors of Afebrile Influenza
A significant proportion of patients with laboratory-confirmed influenza do not present with fever. In a large hospital-based study, about 38% of adults admitted with influenza had no fever at presentation. The absence of fever was more common in older adults, women, those with chronic lung disease, those infected with influenza B, and those who had symptoms for three or more days before seeking care . In children, high fever is very common, but a small percentage may still have influenza without a significant fever .
Diagnostic Value of Symptoms Without Fever
Cough is a particularly important symptom and can be highly sensitive for influenza, even when fever is absent. Studies show that cough alone can be a strong predictor of influenza, especially in children and older adults 47910. Other symptoms such as myalgia, headache, malaise, and sudden onset of illness also contribute to the likelihood of influenza, but none are as specific as fever . In older adults, cough and a general feeling of feverishness (even without a measured fever) are the most predictive symptoms .
Impact of Afebrile Influenza on Diagnosis and Outcomes
Patients with influenza who do not have a fever are less likely to be tested for influenza in emergency settings, receive antiviral treatment less often, and tend to have longer hospital stays and higher mortality rates compared to those with fever . The absence of fever can delay diagnosis and treatment, which may worsen outcomes, especially in vulnerable populations such as the elderly and those with chronic illnesses 110.
Case Definitions and Surveillance Implications
Most clinical case definitions for influenza-like illness (ILI) include fever as a key criterion, often in combination with cough and fatigue 3589. However, relying solely on fever can miss a substantial number of true influenza cases, particularly in older adults and those with certain comorbidities 1510. Surveillance systems and clinicians are increasingly recognizing the need to consider influenza in patients with typical respiratory symptoms, even if fever is absent 145.
Conclusion
Influenza can present without fever, especially in older adults, those with chronic conditions, and in some cases of influenza B. Cough and other respiratory symptoms remain important clues for diagnosis. Clinicians should be aware that the absence of fever does not rule out influenza, and a high index of suspicion is needed to ensure timely diagnosis and treatment, particularly in high-risk groups.
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