Signs suggest US flu activity is starting to recede

For the first time in many weeks, influenza activity in the United States is showing signs of receding, according to today's update from the US Centers for Disease Control and Prevention (CDC).

In other flu news, an international team of researchers yesterday estimated that flu accounts for close to 10% of children's hospitalizations for severe respiratory infections worldwide. The team also reported that flu-related hospitalizations of children are more than three times as common in developing countries as in industrialized nations.

Fewer states reporting high activity

The CDC update said just 7 states and Puerto Rico reported high influenza-like illness (ILI) levels last week, as compared with 14 states and Puerto Rico the previous week. The states are Alabama, Kentucky, New Jersey, New Mexico, New York, North Carolina, and Virginia.

In addition, 8 states and New York City reported moderate ILI activity, down from 13 states a week earlier. But 39 states, 1 fewer than a week earlier, were still reporting geographically widespread flu cases, the CDC reported.

Another declining marker was the estimated share of medical visits attributed to ILI, which dropped from 3.7% 2 weeks ago to 3.2% last week, the agency said. That number was still well above the national baseline of 2.1%.

Also dropping was the proportion of respiratory samples that tested positive for flu: 20.1% of 23,946 specimens last week, versus 23.1% of 25,855 the week before.

Two pediatric deaths noted

The CDC reported 2 flu-related deaths in children for the week, which compares with 8 a week earlier and raises the season total to 30. One death was associated with an H3N2 virus and one with a 2009 H1N1 virus.

One flu marker that rose last week was the share of deaths associated with pneumonia and flu, according to the CDC's 122 Cities Mortality Reporting system. Last week's number was 7.3%, up from 6.9% a week earlier, and just above the epidemic threshold of 7.2%.

The CDC's other system for tracking deaths from pneumonia and flu, run by the National Center for Health Statistics (NCHS), lags 2 weeks behind the 122 Cities system. The NCHS put the number for the week ending Mar 5 at 7.4%, down from 7.5% the previous week and below that week's epidemic threshold of 7.7%.

The cumulative incidence of flu-related hospitalizations for the season reached 18.2 per 100,000 people, up from 14.5 per 100,000 the week before, the CDC reported. Seniors continued to bear the heaviest burden, at 46.1 cases per 100,000, followed by 50- to 64-year-olds (26.9) and children under age 5 (25.6).

International study results

The report on global flu-related hospitalizations in children was published in PLoS Medicine and prepared by a team headed by Kathryn E. Lafond, of the US CDC and the University of Tampere in Finland, as first author.

The team gathered data from 108 published studies on flu-related illness in hospitalized children and from 37 hospital flu surveillance data collections from the Global Respiratory Hospitalizations–Influenza Proportion Positive (GRIPP) working group. The data covered the years from 1982 through 2012.

In a meta-analysis of the data, the researchers calculated that flu was linked to 9.5% of hospitalizations for severe respiratory infection among children under 18 years old worldwide, according to an editor's summary of the report. The figures ranged from 4.8% among children younger than 6 months old to 16.4% among those 5 to 17 years.

The team also estimated that, on average, flu resulted in about 374,000 hospitalizations annually among children under 1 year old and 870,000 hospitalizations annually among children under 5 years.

The researchers further estimated that flu-related hospitalization rates in children under age 5 were more than three times higher in developing countries than in industrialized countries: 150 and 48 hospitalizations, respectively, per 100,000 children per year.

The report cautions that differences in hospitalization practices, case definitions, and flu testing protocols among settings may affect the accuracy of the findings.

The editor's summary says the findings "can be used by countries considering influenza vaccination programs for children and/or pregnant women to help them investigate the possible health and cost implications of such programs."

See also:

CDC FluView report

Mar 25 PLoS Medicine report


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