Influenza Season Still Moderate, But Numbers Continue to Rise

Troy Brown, RN

February 25, 2019

Influenza indicators are still rising and seven more children have died, but the number of people who died from influenza was three times higher last season at this point, according to a report from the Centers for Disease Control and Prevention (CDC).

Influenza-like illness activity was high in 30 states and New York City during the week ending February 16, 2019 (week 7), up from 26 states and New York City the week before. Last season at this point, activity was high in 39 states, New York City, the District of Columbia, and Puerto Rico.

Geographically, influenza-like illness was widespread in 48 states and Puerto Rico for the second week in a row. West Virginia reported regional activity, the District of Columbia reported local activity, and the US Virgin Islands and Hawaii reported sporadic activity. Guam did not report. Last season at this point, influenza activity was widespread in 48 states and Puerto Rico.

Between 17.7 million and 20.4 million individuals have become ill with influenza and 8.2 million to 9.6 million have seen a healthcare provider for influenza-like illness so far this season, according to preliminary in-season estimates from the CDC. This "is the first season CDC has reported in-season burden estimates of flu in the US," the CDC reports.

Deaths From Pneumonia, Flu

The proportion of deaths attributed to pneumonia and influenza (P&I) held steady at 7.0% for the second week in a row during the week ending February 9 (week 6).

"This percentage is below the epidemic threshold of 7.3% for week 3 in the National Center for Health Statistics Mortality Surveillance System. P&I has been at or above threshold for 3 weeks this season. For comparison purposes, over the last five seasons, P&I has been at or above epidemic threshold for a range of 4 weeks (2015-2016) to 16 weeks (2017-2018)," according to an accompanying report summary.

There have been 13,600 to 22,300 influenza deaths from October 1, 2018, through February 16, 2019, the CDC reports in its preliminary estimates.

Seven pediatric deaths were reported during week 7, bringing the total this season to 41; six pediatric deaths were reported during week 6. During week 7 of last influenza season, 13 pediatric deaths were reported for a cumulative total of 97 — more than twice as many as this year.

Six of the children died from influenza A viruses: four influenza A(H1N1)pdm09 viruses and two influenza A viruses for which no subtyping was performed. One child's death was linked to an influenza B virus.

The CDC will report more detailed information on pediatric deaths later in the season.

The cumulative rate of influenza-related hospitalizations was 27.4 per 100,000 population during week 7, compared with 74.5 per 100,000 population at this time last season.

There have been 7922 lab-confirmed influenza-related hospitalizations between October 1, 2018 and February 16, 2019. By this time last year that number was almost three times higher, at 21,279.

Mix of Circulating Influenza A Viruses Shifting

Influenza A(H1N1)pdm09 viruses predominated in six of 10 regions. Influenza A(H3N2) viruses predominated in Region 4 (Alabama, Florida, Georgia, Kentucky, Mississippi, North Carolina, South Carolina, and Tennessee).

During the most current 3 weeks, influenza A(H3) viruses were reported more often compared with influenza A(H1N1)pdm09 viruses in Regions 6 (Arkansas, Louisiana, New Mexico, Oklahoma, and Texas) and 7 (Iowa, Kansas, Missouri, and Nebraska). The two influenza A viruses were seen in approximately equal numbers in Region 2 (New Jersey, New York, Puerto Rico, and the Virgin Islands).

During week 7, 1058 (98.4%) of the 1075 influenza-positive tests reported by public health laboratories to the CDC were influenza A viruses and 17 (1.6%) were influenza B viruses. Of the 996 influenza A viruses for which subtyping was done, 467 (46.9%) were H3N2 viruses and 529 (53.1%) were (H1N1)pdm09 viruses.

Of the 10,210 (26.7%) influenza-positive tests reported by clinical laboratories, 9936 (97.3%) were influenza A viruses and 274 (2.7%) were influenza B viruses.

Almost all (> 99%) viruses tested were susceptible to oseltamivir, zanamivir, and peramivir. No new viruses with decreased susceptibility to antiviral medications were reported during week 7. "So far this season, two (0.2%) influenza A(H1N1)pdm09 viruses displayed highly reduced inhibition by oseltamivir and peramivir," the CDC reports. Another two (0.2%) influenza A(H1N1)pdm09 viruses showed resistance to oseltamivir. All influenza viruses tested were susceptible to zanamivir.

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