The 2019 AFP article on "Influenza: Diagnosis and Treatment," published online ahead of print last week, provides updates on the epidemiology, prevention, and management of influenza. Among this article's highlights are a discussion regarding which patients benefit most from testing, a validated decision rule that can aid this decision to test, and the importance of considering the pros and cons of antiviral medications for patients at low risk for influenza complications.
The article's authors review the classic symptoms of influenza: rapid onset of "cough, fever, myalgias, chills or sweats, and malaise that persists for two to eight days." Patients presenting with this constellation of symptoms have a pre-test probability high enough to obviate the need for testing:
In outpatient and emergency department settings, testing for influenza virus is not necessary to start antiviral treatment in a patient with suspected influenza infection, especially during seasons when influenza A and B viruses are circulating in the local community.A validated clinical decision rule can assist physicians in making, or excluding, the diagnosis as well (fever and cough = 2 points, myalgias = 2 points, chills or sweats = 1 point, symptom onset within the last 48 hours = 1 point). Patients with 2 or fewer points are considered to be at low risk of having influenza, while patients with 4 or more points are considered to be at high risk. It may be most appropriate, then, to target testing for those patients with a moderate risk of influenza (3 points on this scale). Table 3 in the article reviews commercially available point-of-care tests for influenza.
Antivirals should always be prescribed in hospitalized patients, patients at high risk of complications (Table 1), and children younger than 5 years of age. For healthy older children and adults at low risk of complications, however, the CDC is less directive:
Antiviral treatment also can be considered for any previously healthy, symptomatic outpatient not at high risk with confirmed or suspected influenza on the basis of clinical judgment, if treatment can be initiated within 48 hours of illness onset.The AFP authors, however, cite data showing that the cost and side effects of these medications are likely not worth the limited improvement in symptoms:
Given their cost, modest benefits, and adverse effects (primarily nausea and vomiting with oseltamivir), these drugs are not routinely recommended for otherwise healthy patients with influenza.In adults and children treated as outpatients, antiviral treatment does not decrease mortality or hospitalization rates. These medications' side effects can include nausea and vomiting as above "for oseltamivir... Zanamivir can cause bronchospasm, and peramivir can cause diarrhea." Antivirals do decrease the duration of influenza symptoms by about 24 hours when started within 24-36 hours of symptom onset. Family physicians should engage in patient-centered decision making regarding the pros and cons of antiviral treatment in low risk individuals.
Table 4 reviews the antiviral medications currently recommended for treating influenza. Oseltamivir is the first choice for most patients, including patients with severe influenza, pregnant patients, and children under 7 years of age. Since zanamavir is inhaled, it's contraindicated in persons with chronic lung disease. Peravamir is an expensive intravenous option, and baloxavir provides the convenience of single dose treatment.
This entire AFP article is well worth the read as we all prepare for another flu season; there's also an AFP By Topic on Influenza and previous blog posts on the evidence behind antivirals' efficacy, providing effective vaccine counseling, and other ideas to increase influenza vaccination rates if you'd like to read more.