Influenza: Diagnosis and Treatment


Influenza is an acute viral respiratory infection that causes significant morbidity and mortality worldwide. Three types of influenza cause disease in humans. Influenza A is the type most responsible for causing pandemics because of its high susceptibility to antigenic variation. Influenza is highly contagious, and the hallmark of infection is abrupt onset of fever, cough, chills or sweats, myalgias, and malaise. For most patients in the outpatient setting, the diagnosis is made clinically, and laboratory confirmation is not necessary. Laboratory testing may be useful in hospitalized patients with suspected influenza and in patients for whom a confirmed diagnosis will change treatment decisions. Rapid molecular assays are the preferred diagnostic tests because they can be done at the point of care, are highly accurate, and have fast results. Treatment with one of four approved anti-influenza drugs may be considered if the patient presents within 48 hours of symptom onset. The benefit of treatment is greatest when antiviral therapy is started within 24 hours of symptom onset. These drugs decrease the duration of illness by about 24 hours in otherwise healthy patients and may decrease the risk of serious complications. No anti-influenza drug has been proven superior. Annual influenza vaccination is recommended for all people six months and older who do not have contraindications.

Influenza is an acute respiratory infection caused by a negative-strand RNA virus of the Orthomyxoviridae family. There are three distinct types of influenza viruses that infect humans: influenza A, B, and C. Influenza A infects multiple species, including humans, swine, equines, and birds. It is more susceptible to antigenic variation and, hence, is the cause of major pandemics.1,2 The surface of the virion envelope is covered with proteins hemagglutinin (HA), neuraminidase (NA), and matrix 2.1 Antigenic variation is associated with changes in the HA or NA surface proteins and is generally classified as antigenic drift or shift.1 Antigenic drift involves small, gradual amino acid substitutions of the HA or NA proteins that can result in smaller outbreaks. Antigenic shift occurs when there are significant changes in the HA or NA proteins that create novel influenza subtypes with the potential to cause widespread pandemics.1,3 Each influenza A subtype is characterized by numbering both the HA and NA proteins (e.g., H3N2, H5N1).

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The Authors

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DAVID Y. GAITONDE, MD, is a core clinical faculty member and chief of endocrinology service at Dwight D. Eisenhower Army Medical Center, Fort Gordon, Ga....

CPT. FAITH C. MOORE, USA, MC, is a resident in the Department of Internal Medicine at Dwight D. Eisenhower Army Medical Center.

MAJ. MACKENZIE K. MORGAN, USA, MC, is chief of infectious diseases service at Dwight D. Eisenhower Army Medical Center.

Address correspondence to David Y. Gaitonde, MD, Dwight D. Eisenhower Army Medical Center, 300 E. Hospital Rd., Fort Gordon, GA 30905 (email: Reprints are not available from the authors.

Author disclosure: No relevant financial affiliations.


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Published online November 11, 2019



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