140 Times More Early Swine Flu Than Reported
CDC: By August, Up to 5.7 Milllion Americans Had H1N1 Swine Flu
Oct. 29, 2009 - By the end of July, up to 5.7 million Americans -- 140 times
the reported number -- had H1N1 swine flu.
As many as 21,000 were hospitalized by July 23, the CDC now estimates. This
suggests that the current number of H1N1 swine flu-related hospitalizations --
just under 22,000 from the end of August to the middle of October -- is a vast
When reporting numbers of hospitalizations and deaths, CDC officials have
always noted that the data are a guide to the severity of the pandemic and not
a precise tally.
There actually were 79 H1N1 swine flu cases for every lab-confirmed case and
about three pandemic flu-related hospitalizations for every reported
hospitalization through July 23, according to the new estimates from CDC
epidemiologists Carrie Reed, PhD; Lyn Finelli, DrPH; and colleagues.
After July 23, the burgeoning number of flu cases made it necessary to stop
counting lab-confirmed cases -- which the CDC always warned was "
just the tip of the iceberg" -- and to start using mathematical models to
track the pandemic.
"We don't have an update since July 23 with this modelling approach, but as
[CDC Director Thomas] Frieden said last week, we do believe many millions of
people have already contracted this virus here in the U.S.," CDC respiratory
disease chief Anne Schuchat, MD, said today at a news conference.
The key question -- how many millions of Americans have come down with H1N1
swine flu -- remains unanswered. But there's been more than a fivefold increase
in cumulative flu-related hospitalizations and deaths since Aug. 30.
Schuchat warned against applying the multipliers used in the Reed/Finelli
model to current data.
"We don't actually even get reports any more of the individual cases, we
only get summary reports of hospitalizations, so the case multiplier would be a
challenging thing to track," Schuchat said. "The hospitalization multiplier
might also have to be taken with a grain of salt at this time, because of the
possibility that some people were being hospitalized early in this outbreak for
different reasons than they would be now."
Reed, Finelli, and colleagues report their findings in an early
ahead-of-print release from the CDC online journal Emerging Infectious