Influenza Season Winds Down, but Not Done Yet, CDC Says

Troy Brown, RN

May 24, 2019

This influenza season is in its final stages, but influenza is not completely gone just yet, according to the Centers for Disease Control and Prevention's (CDC's) final FluView , which presents data for the week ending May 18 (week 20).

Influenza activity was low for the second consecutive week and outpatient visits for influenza-like illness were below the national baseline for the fifth week in a row, at 1.5%.

Geographically, influenza activity was widespread in Massachusetts; regional in Puerto Rico and Arizona; local in eight states; and sporadic in the District of Columbia, the US Virgin Islands, and 36 states. There was no influenza activity in Alaska, Kansas, Mississippi, and North Carolina. Guam did not report.

Three influenza-related pediatric deaths were reported during week 20, bringing the total this season to 111; two of those occurred during the 2018 - 2019 influenza season and one occurred during the 2017 - 2018 season.

The proportion of deaths attributed to pneumonia and influenza was below the National Center for Health Statistics Mortality Surveillance System's epidemic threshold.

The cumulative rate of laboratory-confirmed influenza-associated hospitalizations per 100,000 population was 65.7; it was highest among adults aged 65 years or older, at 221.7 per 100,000 population. In children aged 0 to 4 years, the hospitalization rate was 73.4 per 100,000 population.

The percentage of respiratory specimens testing positive for influenza in clinical laboratories was low again this week, at 3.8%, after peaking at 26.7% during the week ending February 16 (week 7). Nationally, influenza A(H3) viruses were reported more often than influenza A(H1N1)pdm09 viruses.

Influenza A(H1N1)pdm09 viruses were predominant from October to mid-February, although influenza A(H3N2) viruses have been more commonly seen since late February. Small numbers of influenza B viruses were also reported.

Most influenza A(H1N1)pdm09 and influenza B viruses characterized antigenically were similar to the cell-grown reference viruses representing those used in the 2018 - 2019 Northern Hemisphere influenza vaccines.

"However, the majority of influenza A(H3N2) viruses are antigenically distinguishable from A/Singapore/INFIMH-16-0019/2016 (3C.2a1), a cell-propagated reference virus representing the A(H3N2) component of 2018-19 Northern Hemisphere influenza vaccines," the CDC writes in the report.

The "vast majority" of influenza viruses tested (> 99%) were susceptible to oseltamivir and peramivir. All were susceptible to zanamivir and baloxavir.

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