Flu activity stays low in most Northern Hemisphere regions

Flu activity remains low in Northern Hemisphere countries, though some indicators showed slight upticks that could signify that the influenza’s summer slumber in the region is ending, according to national, regional, and international activity reports.

In the United States, flu markers remained below seasonal thresholds in all parts of the country, with the percentage of clinic visits for influenza-like illness (ILI) at 1.2%, well below the baseline of 2.0%, the US Centers for Disease Control and Prevention (CDC) said in its first full-length FluView report of the season.

A government shutdown earlier this month delayed and shortened the CDC’s weekly flu reports. The agency published some of the unreported data in an overview of US and international flu activity over the summer months in Morbidity and Mortality Weekly Report (MMWR) today.

In that report, the CDC said US flu activity during the summer months was similar to previous years, with the exception of the 2009 H1N1 pandemic. Antigenic testing of strains circulating in the United States over the summer suggests that they are similar to the strains included in the vaccine for 2013-14 flu season, the agency added, though it's impossible to predict which strains will predominate or how severe the season will be.

In the CDC's FluView report for the week ending Oct 19, the percentage of respiratory samples that tested positive for flu was 3.8%, a decrease from the previous week, when 4.7% of samples were positive.

Two pediatric flu deaths were reported, both of which occurred during the 2012-13 season, raising the total for that season to 167. Both of the newly reported deaths were from influenza B. Overall percentage deaths from pneumonia and flu weighed in last week at 5.8%, putting the figure below the 6.2% epidemic threshold for the week.

The number of states or territories reporting regional and local geographic spread of flu last week remained the same as the previous week, one and four, respectively, but the number of states reporting sporadic activity rose from 24 to 27.

Meanwhile, the Public Health Agency of Canada (PHAC) said today that the country’s flu activity remained at interseasonal levels last week. Though clinic visits for ILI have gradually increased over the past 5 weeks, few lab detections of flu have been reported. The agency added that rhinovirus and parainfluenza were the predominant circulating viruses last week.

Internationally, flu detections in the Northern Hemisphere’s temperate regions remain low, though ILI activity is starting to pick up in many European countries, the World Health Organization (WHO) said yesterday.

Flu activity varies across tropical Asian countries, with levels of predominantly H3N2 declining in Hong Kong but flu detections increasing in southern China, where health officials are watching to see if the number of novel H7N9 flu infections will start rising again after a summer lull. Two cases have already been reported this month.

In the Southern Hemisphere, where the flu season is wrapping up, flu detections and activity declined in Australia and New Zealand, both of which saw a late-season rise.

The European Centre for Disease Prevention and Control (ECDC) in its weekly update today characterized the region’s flu activity as low, with only three countries reporting sporadic activity: Denmark, France, and Norway. It noted that Sweden and Northern Ireland reported increasing trends, with stable trends reported in other countries.

See also:

Oct 25 CDC weekly flu update

Oct 25 MMWR report

Oct 25 PHAC Flu Watch

Oct 24 WHO influenza update

Oct 25 ECDC influenza update

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