US flu data show season ramping up

In what many experts predict may be a severe influenza season, the US Centers for Disease Control and Prevention (CDC) today reported signs that flu activity is stepping up, about 3 weeks earlier than it did last season.

In its weekly FluView report, which includes data through the week that ended Nov 25, the CDC said outpatient levels of influenza-like illness (ILI) are elevated in 4 of the country's 10 regions, and the proportion of visits to doctors' offices for ILI topped the national baseline for the first time this season.

In related news, CDC researchers reported that about 8% of Americans contract the flu each year, and European officials are still reporting low influenza levels.

Three states with high ILI

The CDC today said the proportion of outpatient visits for ILI has now reached 2.3%, above the national baseline of 2.2% and up from 2.0% the week before. Last year the CDC did not report that level of ILI till Dec 23.

Three southern states—Louisiana, Mississippi, and South Carolina—are experiencing high ILI activity, which is up from two the previous week. In addition, Georgia is reporting moderate ILI activity.

The number of states confirming widespread geographic spread doubled, from two to four, with Georgia and Massachusetts joining Louisiana and Oklahoma in that category. Guam and 10 states reported regional flu activity in today's report, and Puerto Rico and 24 states noted local activity.

The CDC said the country had a cumulative rate of 2.0 lab-confirmed flu-related hospitalizations per 100,000 population last week, which was up from 1.4 the week before. Among seniors, the rate was 7.3 per 100,000 population.

The percentage of deaths attributed to pneumonia and flu was 5.7%, up slightly from 5.6% the week before but still well below the national epidemic threshold of 6.5%. The CDC reported no new flu-related deaths in children after reporting five in the previous report.

Of respiratory specimens that tested positive for flu last week, 75.6% were influenza A and 24.4% were influenza B. About 90% of the "A" viruses were the H3N2 strain, a harbinger of a more severe flu season, due to its impact on seniors, young children, and likely protection gaps related to egg-based flu vaccine production.

Low levels in Europe

In Europe, meanwhile, influenza activity across the continent remains at low levels but is rising, officials from the European Centre for Disease Prevention and Control (ECDC) and the World Health Organization's (WHO's) European office reported today.

Of respiratory samples tested, 6.3% tested positive for influenza, which is up from 3.7% the week before. Data on all-cause mortality from 21 nations indicate it is within normal ranges.

Although it's based on only 35 isolates, about 59% were H3N2 strains that genetically match the H3N2 strain in the vaccine, the ECDC/WHO report said.

Annual flu incidence

In research news, CDC scientists, noting that the seasonal incidence of flu in the United States is often cited as ranging from 5% to 20%, analyzed nationwide data from 2010 to 2016 and found it was about 8%, with a range of 3% to 11%, according to their study today in Clinical Infectious Diseases.

The investigators reported results derived from two methods to estimate flu rates based on data collected as part of national surveillance. They estimated that the annual influenza incidence ranged from 3.0% to 11.3% among the six seasons, with a median incidence of 8.3% for all ages, 9.3% for children, and 8.9% for adults 18 to 64 years old using a statistical method. The other method, a meta-analysis, yielded rates of 7.1%, 8.7%, and 5.1%, respectively.

See also:

Dec 1 FluView report

Dec 1 CDC FluView summary

Dec 1 ECDC update

Dec 1 Clin Infect Dis study

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