Flu season is upon us early this year, hitting older adults and children under 4 the hardest, according to the Centers for Disease Control and Prevention (CDC).

"Nationally, [influenza-like illness] activity has been at or above baseline for 2 weeks; however, the amount of influenza activity across the country varies, with the south and parts of the west seeing elevated activity while other parts of the country are still seeing low activity," the CDC explains in a report for the week ending November 16 (week 46).

"There is significant cocirculation of influenza A(H3N2), A(H1N1)pdm09 and B/Victoria viruses with the predominant virus varying by region and age group," the agency reports.

The percentage of outpatient visits (2.5%) for influenza-like illness exceeded the baseline (2.4%) for the first time during the week ending November 16 (week 46); last season, that happened during the week ending November 24 (week 47), when the percentage was 2.3% with a baseline of 2.2%.

The number of jurisdictions reporting regional or widespread activity rose to 15, up from 10 during week 45.

Influenza-like illness activity was high in Puerto Rico and seven states (Alabama, Arkansas, Georgia, Mississippi, Nevada, South Carolina, and Texas) and low in 12 states (Alaska, Arizona, California, Colorado, Connecticut, Hawaii, Maryland, New Jersey, New Mexico, Oklahoma, Tennessee, and Virginia).

Influenza activity was minimal in the District of Columbia and 30 states; there were insufficient data to calculate activity levels in the US Virgin Islands and Louisiana.

Influenza-like illness activity was widespread in six states (Alabama, California, Louisiana, Massachusetts, Nevada, and South Carolina) and regional in nine states (Arizona, Connecticut, Florida, Georgia, Hawaii, New Mexico, Oregon, Tennessee, and Texas).

Influenza activity was local in Puerto Rico and 23 states and sporadic in the District of Columbia, the US Virgin Islands, and 11 states. There was no activity in Rhode Island and Guam did not report.

According to the Influenza Hospitalization Surveillance Network (FluSurv-NET), there were 393 laboratory-confirmed influenza-associated hospitalizations between October 1 and November 16, for an overall hospitalization rate of 1.4 per 100,000 population.

The highest rates were seen among adults aged 65 years or older (3.6 per 100,000), children aged 0 to 4 years (2.2 per 100,000), and adults aged 50 to 64 years (1.4 per 100,000). Rates are similar to those seen at this point during other recent influenza seasons.

Of those 393 hospitalizations, 246 (62.6%) were related to influenza A virus, 142 (36.1%) to influenza B virus, and 3 (0.8%) to co-infection with influenza A and influenza B viruses. Two hospitalizations were associated with influenza virus that had not undergone typing.

Among influenza A viruses for which subtype information was available, 28 (50%) were A(H1N1)pdm09 virus and 28 (50%) were A(H3N2).

Influenza season is just beginning and there is still time to get vaccinated, CDC advises: "Flu vaccination is always the best way to prevent flu and its potentially serious complications."

CDC FluView. Published online November 22, 2019. Full text

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