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 Six children died from the flu during the last full week in
December, bringing the total flu deaths to 21 this season, the
report showed.
Last week the CDC reported for the first time that deaths from flu
and pneumonia reached an epidemic level, comprising 6.8 percent of
all deaths. That figure slipped slightly below the epidemic level in
this week's report, the CDC said.
"Last week was the first week that this particular number exceeded
the epidemic threshold, but we've been in a flu epidemic for weeks
now," said Dr. Michael Jhung, medical officer in the Centers for
Disease Control and Prevention's Influenza Division.
The statistic is just one of many clues the CDC uses to gauge the
severity of flu in the United States, which has a widespread
outbreak - or an epidemic - every year.
Jhung reviews several factors when determining whether the flu
season has started, suggesting the nation is in a period of
epidemic. Initially, he considers the percentage of positive flu
tests. When that exceeds 10 percent for 2 weeks, the season is
starting. That happened around mid-November this season.
He also looks at the proportion of patients seeking care for
influenza-related illnesses. When that exceeds 2 percent of visits,
it is another sign of a flu epidemic.
This season, flu watchers are keenly focusing on hospital admissions
because the current vaccine may not be a good match for the most
common seasonal flu strain circulating in the United States known as
influenza A (H3N2) virus.
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Flu seasons dominated by H3N2 tend to have higher overall
hospitalization rates and more flu-related deaths, especially among
older people and very young children compared with flu seasons
dominated by the H1N1 virus or influenza B viruses.
In the latest CDC report, flu hospitalizations, a key measure of
severity, have reached 12.6 per 100,000 for all ages. Last season,
the rate was 5.8 per 100,000 and in 2012, the most recent season
dominated by H2N3, the rate was 8.1 percent.
"We are above that now," Jhung said, suggesting this flu season "is
at least as severe as 2012 was."
(Reporting by Julie Steenhuysen; Editing by Richard Chang)
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