Outpatient flu visits spike as more states note high activity

The proportion of people visiting outpatient clinics with influenza-like illness (ILI) symptoms is now 3.5%, well above the national baseline of 2.2% and up from 2.7% the week before, the Centers for Disease Control and Prevention (CDC) said today in its weekly flu update.

Those visits are occurring across the country, as 10 states (Alabama, Arizona, Arkansas, Kentucky, Louisiana, Mississippi, Nevada, Oklahoma, South Carolina, and Texas) now report high ILI activity in the week that ended Dec 16, up from 4 the week before. Puerto Rico and eight states (California, Georgia, Illinois, Kansas, Missouri, Nebraska, Oregon, and West Virginia) experienced moderate ILI activity, and 11 states experienced low ILI activity (Alaska, Colorado, Connecticut, Massachusetts, Michigan, Minnesota, New Jersey, New Mexico, South Dakota, Virginia, and Wyoming). The remaining 21 states reported minimal flu activity.

Flu activity is at or above region-specific baselines in 9 of 10 US regions. Last week, only 7 regions reported activity above baselines.

Flu is now widespread in 23 states, up dramatically from 12 the week before.

The CDC also reported one pediatric influenza death. The death was associated with an influenza A H1N1 virus and occurred last week. There have been nine confirmed pediatric influenza deaths this season.

No cases of variant influenza were reported this week.

Hospital cases rise

The overall hospitalization rate was 6.2 lab-confirmed cases per 100,000 population, up from 4.3 per 100,000 the week before. A total of 1,772 lab-confirmed influenza-associated hospitalizations were reported between Oct 1 and Dec 16, 540 of those between Dec 10 and Dec 16.

Hospitalization rates were highest for adults older than 65 years (25.3 per 100,000 population), followed by adults aged 50 to 64 (6.5 per 100,000 population), and children aged 0 to 4 years (4.7 per 100,000 population).

The vast majority of  hospitalized cases (1,567 cases, or 88.4%) were associated with influenza A virus, 192 (10.8%) with influenza B virus, 5 (0.3%) with influenza A virus and influenza B virus co-infection, and 8 (0.5%) with influenza virus for which the type was not determined. According to the CDC, among those with influenza A subtype information, 396 (87.0%) were A(H3N2) and 59 (13.0%) were A(H1N1)pdm09 virus.

Overall, influenza A was still the dominant strain among all samples tested at clinical laboratories last week. A total of 85% of viruses were influenza A, with influenza B representing the remaining 15% of samples. Among subtypes of influenza A samples, 88.7% were  H3N2, 8.4% were H1N1, and subtyping was not performed on 2.9%.

Uptick in flu activity in Europe

In other flu news, the European Centre for Disease Prevention and Control (ECDC) reported high flu activity in western Europe, Scandinavia, and Turkey this week. Both influenza A H3N2 and influenza B/Yamagata viruses are circulating throughout the region.

See also:

Dec 22 CDC FluView

Dec 22 ECDC flu update

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