CDC Reports Increased Flu Rates to End 2018

As of the end of December, the rate of outpatient visits for influenza-like illnesses (ILIs) had nearly doubled from the national baseline, as the 2018-19 influenza (flu) season continues to see a variation of influenza A strains predominately affect the country.

According to the US Centers for Disease Control and Prevention’s (CDC’s) Weekly US Influenza Surveillance Report for the week ending December 29, the reported rate of outpatient visits for ILI had increased to 4.1%—well above the national baseline of 2.2%. That rate had increased 1.5% in just 2 weeks, after the CDC had reported a 2.7% rate during the week ending December 15.

All 10 regions of focus under the CDC’s flu surveillance reported ILIs at or above their respective baseline levels—an increase they believe could be due to the reduction in healthcare visits during the holiday season.

Regionally, New York City and 19 states reported high ILI activity, a significantly greater rate than states and US territories to report moderate (9), low (11), or minimal (12) ILI activity. Among the 10 regions, the Atlanta-based region (including Alabama, Florida, Georgia, Kentucky, Mississippi, North Carolina, South Carolina, and Tennessee) reported the greatest rate of respiratory specimens positive for flu observed in clinical laboratories (19.5%), well above the national rate of 13.7%.

The Atlanta region, which is the only region among the 10 to be predominately affected by the influenza A(H3) strain in the past 3 weeks, also leads all regions in total jurisdictions reporting either regional or widespread activity (7 of 8). Including the other regions—in which the influenza A(H1N1)pdm09 strain is the most predominant in each—43 of the US’ 54 jurisdictions are now reporting flu activity at regional or widespread levels.

The high prevalence of A(H1N1)pdm09 strain—currently 81.4% of all positive specimen tests—is a deviation from last year’s flu season, when the H3N2 mutation strain was prevalent in about 90% of all flu cases reported through mid-January 2018. This year, the mutated strain accounts for just 18.6% of all cases.

While the past flu season was noted it for its higher rate of severe infections—due to the mutated strain being less affected by vaccination strains—clinicians compared it to similarly difficult seasons, including the 2014-15 and 2012-13 seasons.

At this time last year, an estimated 16 children younger than 5 years old, per 100,000 population, were hospitalized due to the flu. As of last week, this flu season had hospitalized 14.5 children younger than 5 years old, per 100,000 population. In both seasons, that rate is the greatest among all observed age groups.

The 185 influenza-associated pediatric deaths reported last season were the greatest total in the last 4 years. Through 2018, the CDC reported just 13 influenza-associated pediatric deaths—89.9% less than the average US pediatric death total reported in the previous 3 seasons (116.6).

The Weekly US Influenza Surveillance Report was published online on the CDC's website.