POC influenza testing: State of the art
With point-of-care (POC) molecular assays, pediatricians can diagnose influenza A and B during the office visit.
Each year in the United States, seasonal flu is responsible for dozens of deaths and thousands of hospitalizations among children, especially those with underlying medical conditions. Rapid diagnosis identifies those children who would be candidates for antiviral therapy that can shorten the course of illness and lessen symptom severity. Unfortunately and until recently, rapid office tests for influenza have been very unreliable. With the introduction of point-of-care (POC) molecular assays, pediatricians can diagnosis influenza A and B during the office visit with sensitivity and specificity comparable to reference assays.
This article will review influenza—its presentation, symptoms and treatment—and review the POC influenza tests currently available to help expedite diagnosis.
The 2 influenza viruses that cause human epidemics are Influenza A and B. Influenza A is categorized into subtypes based on hemagglutinin and neuraminidase protein antigens. Hemagglutinin is responsible for the entry of the virus into cells, while the neuraminidase facilitates the release of virus from host cells. Influenza B is not categorized into subtypes and is separated into 2 genetic lineages: Yamagata and Victoria.
The US Food and Drug Administration (FDA) has recommended that the 2016-2017 influenza trivalent vaccines used in the United States contain an A/California/7/2009 (H1N1) pdm09-like virus, an A/Hong Kong/4801/2014 (H3N2)-like virus, and a B/Brisbane/60/2008-like virus (B/Victoria lineage). It also recommends that quadrivalent vaccines, which have 2 influenza B viruses, contain the viruses recommended for the trivalent vaccines, as well as a B/Phuket/3073/2013-like virus (B/Yamagata lineage). This represents a change in the influenza A(H3N2) component and a change in the influenza B lineage included in the trivalent vaccine compared with the composition of the 2015-2016 influenza vaccines. As recently reported in the medical and popular press, the live attenuated influenza vaccine (LAIV) is not recommended for prophylaxis this season because of its lack of efficacy.
According to the American Academy of Pediatrics Committee on Infectious Disease (aka, the Red Book), influenza viruses are spread through coughing and sneezing as well as with contact with respiratory droplets on surfaces. The incubation period for the disease is 1 to 4 days, and patients shed virus and are considered contagious for 1 day before symptoms begin and during the course of the illness.
Typically, influenza begins in November and lasts until May, with peak season usually from January to March of each year. Symptoms include chills, fever, sore throat, headache, and cough, with myalgia being a very predominant symptom. It is estimated that 10% to 40% of children are infected in any given year.1 Children aged younger than 2 years and patients with an underlying medical condition are at particular risk of contracting severe disease. High-risk patients include those having:1
· Asthma or other chronic pulmonary diseases, such as cystic fibrosis;
· Hemodynamically significant cardiac disease; â¨
· Immunosuppressive disorders or therapy (see Special Considerations, Red Book, page 488); â¨
· Human immunodeficiency virus (HIV) infection;
· Sickle cell anemia and other hemoglobinopathies;â¨
· Diseases that necessitate long-term aspirin therapy, including juvenile idiopathic arthritis or Kawasaki disease; â¨
· Chronic renal dysfunction;â¨
· Chronic metabolic disease, including diabetes mellitus; and â¨
· Any condition that can compromise respiratory function (eg, neurodevelopmental disorders, seizure disorders).