Most of the country is experiencing high influenza-like illness activity and 800 more deaths were reported during the last week of 2019 alone, according to the most recent report from the Centers for Disease Control and Prevention (CDC).

Influenza has caused at least 6.4 million illnesses, 55,000 hospitalizations, and 2900 deaths so far this season; influenza activity has been elevated for 8 weeks.

The percentage of outpatient healthcare provider visits for influenza-like illness (ILI) rose from 5.1% to 6.9% during the week ending December 28 (week 52). "The increase in the percentage of patient visits for ILI during week 52 compared to week 51 may be influenced in part by a reduction in routine healthcare visits surrounding the holidays occurring during week 52 as has occurred during previous seasons," the CDC says. The national baseline is 2.4%.

Nationally, influenza B/Victoria viruses are predominant, followed by A(H1N1)pdm09 viruses. "A(H3N2) and B/Yamagata viruses are circulating at very low levels," the CDC reports. Influenza B viruses do not usually predominate this early in the season.

Predominant viruses differ by region and age group, the CDC explains. Influenza B/Victoria viruses are most common among children aged 4 years and younger (48% of reported viruses) and those aged 5 to 24 years (59% of reported viruses).

Influenza A(H1N1)pdm09 are the most common viruses among adults aged 25 to 64 years (42% of reported viruses) and those aged 65 years and older (43% of viruses).

Geographically, influenza activity was widespread in Puerto Rico and 45 states, regional in four states (Kansas, Maine, North Dakota, and Vermont), local in the District of Columbia and Hawaii, and sporadic in the US Virgin Islands. Guam did not report influenza activity.

Influenza-like illness activity was high in the District of Columbia, New York City, Puerto Rico, and 34 states (37 jurisdictions), compared with 28 jurisdictions during the previous week.

Activity was moderate in nine states (Florida, Maine, Minnesota, New Hampshire, Ohio, Rhode Island, South Dakota, Vermont, and Wyoming), low in five states (Hawaii, Michigan, Missouri, Montana, and Nevada), and minimal in Delaware and Idaho.

Hospitalization Highest Among Older Adults

Overall, the hospitalization rate was 9.2 per 100,000. "This is similar to what has been seen at this time during recent seasons," the CDC notes in its report.

The hospitalization rate was highest among older adults aged 65 years or older (19.9 per 100,000), followed by young children aged 0 to 4 years (17.8), and adults aged 50 to 64 years (10.0).

Just more than half (1374; 51.5%) of 2667 hospitalizations were linked to influenza A virus and 47.8% (1274) were associated with influenza B virus. Less than 1% were associated with influenza A virus and influenza B virus co-infection and 0.3% had no influenza virus type determination. Most (80.7%) influenza A viruses that underwent subtyping were A(H1N1)pdm09 and 19.3% were A(H3N2) viruses.

Pneumonia and influenza were responsible for 5.5% of deaths during week 51 — below the epidemic threshold of 6.8%.

Five pediatric deaths associated with influenza occurred during weeks 50 and 51 and were reported to CDC during week 52, bringing the total to 27. Three deaths were linked to influenza A viruses and two resulted from influenza B viruses.

Of 27 deaths that have been reported this season, 18 were linked to influenza B viruses (five of these had the lineage determined and all five were B/Victoria viruses). Nine deaths were linked to influenza A viruses; four of these were subtyped and all four were A(H1N1)pdm09 viruses.

The percentage of respiratory specimens that tested positive in clinical laboratories rose to 26.3%, up from 23% the week before.

The CDC urges everyone to get vaccinated against influenza if they have not already, and says antiviral medications are also important: "Almost all (>99%) of the influenza viruses tested this season are susceptible to the four FDA-approved influenza antiviral medications recommended for use in the US this season."

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