Using new methodology, the Centers for Disease Control and Prevention has revised its estimate of the total number of deaths caused by swine flu. The new figures will result in a tripling of the number deaths from H1N1overnight.
While the official estimates have not yet been released, it appears that the tally of deaths from the novel form of influenza will rise to around 4,000, up from 1,200, as first reported Wednesday by The New York Times.
The changes reflect new surveillance methods thought to be more accurate but also show that figuring out the death toll from influenza is not a precise science.
"We don't really know how many cases of H1N1 there have been, truly," said Dr. Len Horovitz, a pulmonary specialist at Lenox Hill Hospital in New York.
The problem is the difficulty of testing every patient to confirm a diagnosis, which is outweighed by the benefits of immediately treating patients for flulike symptoms.
"Seasonal flu numbers are very soft, based on excess deaths more than diagnoses," explained John Barry, author of "The Great Influenza." "Many, if not most, of the deaths attributed to influenza in seasonal flu are quite indirect."
"Each case of influenza is not reported either with seasonal flu or in a pandemic [like H1N1] and therefore the subsequent deaths are not always immediately traceable to a specific cause of death," said Dr. Frank James, a health officer in San Juan County, Wash., and a clinical associate professor at the University of Washington.
Ultimately, James explained, the estimates are redone when officials have a better sense of the disease's infection and mortality rates.
"The public will struggle with this change and some will take it to mean that the government does not know what it is talking about while those that think more clearly will understand the process and outcome and reasons for the difference," he said.
Glen Nowak, a spokesman for the CDC, explained that some of the agency's previous estimates had limitations -- for example, people with pneumonia unrelated to H1N1 may have been included -- and the agency plans to release its estimate of the death toll today, if all goes as planned.
But doctors stressed that the death toll revision was not a cause for worry.
"I don't really think the public should be more worried, as the revised estimate does not reflect a change in the virulence of, or severity of, infection due to the virus," said Dr. Christopher Ohl, an associate professor of medicine in the infectious disease division at Wake Forest University School of Medicine.
The death toll from H1N1 may alarm many, but it is the population affected rather than sheer numbers of deaths that has had more impact.
"I'm not sure how closely the public has been following the numbers -- 4,000 seems a small fraction of the 36,000 estimated to die of seasonal influenza each year, but these deaths are in younger people, so it may raise consciousness further," said Dr. George Rutherford, director of the University of California, San Francisco, Institute for Global Health. "Just because you haven't gotten to 36,000 doesn't mean it's not bad."