US Influenza Activity Dropping, but Hospitalizations Up, CDC Says

Troy Brown, RN

April 07, 2020

Influenza activity is decreasing in the United States, but hospitalization rates rose slightly, according to an April 3 report from the Centers for Disease Control and Prevention (CDC).

The number of influenza cases confirmed in clinical laboratories fell "sharply" and is low at this time, the CDC said. Influenza-like illness (ILI) activity is lower than in the previous week reported by the agency but remains elevated.

High hospitalization rates are still being seen among children and young adults.

"Recent changes in healthcare seeking behavior, including increasing use of telemedicine and recommendations to limit emergency department (ED) visits to severe illness, as well as increasing levels of social distancing, are affecting the number of persons with ILI and their reasons for seeking care in outpatient and ED settings," the CDC explained.

The percentage of respiratory specimens testing positive for influenza in clinical laboratories fell from 7.3% the previous week to 2.1% for the week ending March 28.

Nationally, the most frequently reported influenza viruses this season are influenza A(H1N1)pdm09 viruses.

Outpatient healthcare visits for ILI fell to 5.4% from 6.3% last week. In all regions in the United States, levels are above baselines.

The number of jurisdictions with high influenza activity fell from 37 last week to 31 this week. The number of jurisdictions with widespread influenza activity fell from 49 to 41 this week.

The overall cumulative hospitalization rate this season rose from 67.3 to 67.9 per 100,000 population. Hospitalization rates were highest among those aged 65 years or older (178.8 per 100,000), followed by children aged 0 to 4 years (93.9), adults aged 50 to 64 years (89.7), adults aged 18 to 49 years (35.5), and children aged 5 to 17 years (24.6).

Hospitalization rates are the highest on record for any season for those aged 0 to 4 years and 18 to 49 years with the exception of the 2009 H1N1 pandemic.

The percentage of deaths related to pneumonia and influenza rose from 7.3% to 8.2% — above the epidemic threshold of 7.2%. "The increase is due to an increase in pneumonia deaths rather than influenza deaths and may be associated with COVID-19," the CDC explained in the report.

Seven pediatric deaths were reported this week, bringing this season's total to 162. With the exception of the 2009 pandemic, pediatric deaths are the highest since reporting began in 2004–2005.

According to the CDC, at least 39 million influenza illnesses, 400,000 hospitalizations, and 24,000 deaths have occurred that were related to influenza.

"The COVID-19 pandemic is affecting healthcare seeking behavior. The number of persons and their reasons for seeking care in the outpatient and ED settings is changing. These changes impact data from ILINet [US Influenza Surveillance System] in ways that are difficult to differentiate from changes in illness levels, therefore ILINet data should be interpreted with caution," the CDC explained.

Antiviral medications are important for the treatment of influenza, and more than 99% of influenza viruses tested during this season have been susceptible to the four influenza antiviral medications approved by the US Food and Drug Administration this season.

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