Diagnosis of seasonal influenza in adults
- Raphael Dolin, MD
Raphael Dolin, MD
- Professor of Medicine
- Harvard Medical School
Influenza is an acute respiratory illness caused by influenza A or B viruses that occurs in outbreaks and epidemics worldwide, mainly during the winter season. Signs and symptoms of upper and/or lower respiratory tract involvement are present, along with indications of systemic illness such as fever, headache, myalgia, and weakness. Although acutely debilitating, influenza is a self-limited infection in the general population. However, it is associated with increased morbidity and mortality in certain high-risk populations.
In certain circumstances, the diagnosis of influenza can be made clinically, such as during an outbreak. At other times, it is important to establish the diagnosis using laboratory testing quickly, such as in the hospitalized patient with acute onset of severe pulmonary disease.
The diagnosis of seasonal influenza in adults will be reviewed here. The diagnosis of this infection in children is discussed separately. The epidemiology, clinical manifestations, prevention, and treatment of seasonal influenza infection, as well as the diagnosis of pandemic H1N1 influenza ("swine influenza") and avian influenza, are reviewed elsewhere. (See "Seasonal influenza in children: Clinical features and diagnosis" and "Epidemiology of influenza" and "Clinical manifestations of seasonal influenza in adults" and "Seasonal influenza vaccination in adults" and "Prevention of seasonal influenza with antiviral drugs in adults" and "Infection control measures to prevent seasonal influenza in healthcare settings" and "Treatment of seasonal influenza in adults" and "Clinical manifestations and diagnosis of pandemic H1N1 influenza ('swine influenza')" and "Clinical manifestations and diagnosis of avian influenza".)
During outbreaks — During an influenza outbreak, acute febrile respiratory illnesses brought to the attention of clinicians can be diagnosed as influenza with a high degree of certainty by clinical criteria. This was demonstrated in the following studies:
●In a retrospective pooled analysis of signs and symptoms in 3744 adolescents and adults with an influenza-like illness who participated in phase II and III trials of neuraminidase inhibitors during outbreaks . The best multivariate predictor was the combination of fever and cough within 48 hours of the development of symptoms, which had a positive predictive value of 79 percent for documented influenza.
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- CLINICAL DIAGNOSIS
- During outbreaks
- Sporadic cases
- Older adult patients
- LABORATORY TESTING
- Rapid antigen tests
- Nucleic acid tests
- Viral culture
- Serologic testing
- APPROACH TO DIAGNOSIS
- Whom to test
- - H3N2 variant viruses
- Type and handling of specimens
- Choice of diagnostic test
- Interpretation of results
- INFLUENZA ACTIVITY
- INFORMATION FOR PATIENTS
- SUMMARY AND RECOMMENDATIONS