What You Need to Know About the CDC's Recent Flu Update for Clinicians

As the flu continues to beat down on the United States, and hospitalization rates exceed milestones set during the 2014-2015 season, another high severity, H3N2-predominant season, experts from the Centers for Disease Control and Prevention (CDC) provided a flu update for clinicians via a Clinician Outreach and Communication Activity (COCA) Webinar.

An overview of the many resources available for flu surveillance, most notably, the weekly Flu View report, was provided. Alicia P. Budd, MPH, an epidemiologist in the Influenza Division of the CDC’s National Center for Immunization and Respiratory Diseases shared some of the information from the most recent report on week 4, ending in January 27, 2018.

Dr. Budd shared that although influenza A H3N2 has been the predominant strain of the virus this season, influenza A (H1N1)pdm09 and influenza B viruses are also circulating.

Discussing influenza-like illness (ILI), she mentioned that the season is following the expected range of elevated activity. At the end of December 2017, the percentage of ILI “was tracking like what we saw before in H3N2 predominant seasons,” shared Dr. Budd. However, outpatient ILI levels this season have continued to increase, and are the highest we’ve seen since the pandemic in 2009.

As for hospitalization rates, this season’s rates for all age groups combined are higher in week 4 than any of the prior 6 flu seasons. Seasons in which the A (H3N2) strain predominates are often linked with higher mortality and hospitalization rates among older adults and young children.

Dr. Budd also discussed the widespread activity of the virus in most of the United States; activity began to increase in November 2017 and has remained elevated through January 2018.

Although it is not possible to know how severe the season will be, “several indicators are as high or higher than what was seen in the 2014-2015 season, a high severity A(H3N2) predominant season,” according to Dr. Budd.

She added that we can expect high levels of activity in the coming weeks and that activity on the east coast appears to be increasing.

Tim Uyeki, MD, MPH, MPP, chief medical officer of the Influenza Division of the CDC’s National Center for Immunization and Respiratory Diseases provided information on the pathogenesis of the virus, associated symptoms and complications, testing, and treatment.

Most patients who become infected with influenza tend to experience relatively mild, uncomplicated illness, although disease severity and clinical manifestations can vary by age, host factors, immunity, and the strain of the virus.

Adults 65 or older, young children 2 or younger, those with chronic medical conditions, pregnant women, nursing home residents, and American Indian or Alaskan Native individuals were identified as those who are at high-risk for developing influenza complications, and thus, can experience severe influenza. However, Dr. Uyeki noted that some otherwise healthy persons can experience severe influenza complications as well.

With regards to testing, Dr. Uyeki highlighted a number of different influenza test, including:

• Molecular assays, which have high sensitivity and high specificity. Rapid molecular assays are capable of yielding results between 15 and 30 minutes; some of these are CLIA-waived. For reverse transcription polymerase chain reaction (RT-PRC), nucleic acid detection assays, it can take anywhere from 45 to 80 minutes to 4 to 8 hours for results.
• Antigen detection, which has low to moderate sensitivity. Rapid influenza diagnostic tests take 10 to 15 minutes for results, while direct florescent antibody staining takes anywhere from 2 to 4 hours.
• Viral culture, which include shell-vial (takes 1 to 3 days) and tissue culture, embryonated egg culture (which take 3 to 10 days).

“Proper interpretation of results is important,” Dr. Uyeki stressed, especially when it comes to negative results. Influenza testing is not needed for all outpatients but testing with a molecular assay is recommended for hospitalized patients.

“For antiviral treatment, 1 class is recommended: the neuraminidase inhibitors (NAIs),” he continued. This treatment is recommended as soon as possible for hospitalized patients, high-risk outpatients, and those with progressive disease.”

For more information on the year’s flu season, be sure to check back on our website tomorrow for this week’s Contagion® Flu Update.