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."
A new study published in the journal Lancet looking at the toll of H1N1 deaths in Mexico shows that while the virus afflicts the young more often, it also seems to have killed a higher percentage of elderly patients there.
However, doctors questioned whether swine flu would have the same effect in the United States. Horvitz noted that reporting methods for influenza in Mexico are different from those here. Rutherford, meanwhile, noted that the more rural nature of the country means that older people living in more remote areas would not have gained the immunity that older Americans gained from previous strains of the virus that spread.
The number of younger people affected has been one of the driving forces behind concerns about swine flu.
"It's a very different calculation if any illness is killing people 80 years old instead of 8 years old," said Laurie Garrett, a senior fellow for global health at the Council on Foreign Relations.
She explained that even if the death toll is lower than that of other years, the number of years of life lost may be much higher.
But others said H1N1 needs to be compared to other hazards of daily life.
"While 4,000 deaths seem like a lot more than 1,200, and each death is a tragedy, it still appears that the effects of H1N1, although widespread are quite mild," said Dr. Gabe Kelen, director of the department of emergency medicine at Johns Hopkins.
He said that most of the deaths in younger people, while upsetting, were in those who had underlying conditions -- a similar pattern to deaths in the elderly during annual flu seasons.
"We also need to put the deaths in perspective," said Kelen. "Society seems to accept deaths from drunk drivers, and shootings without the type of alarm that H1N1 engenders. Dying from H1N1 is less likely than being hit by a drunk driver or being shot in many parts of the country." However, unfortunately, he concluded, "There's no vaccine to protect against impaired drivers or for acute lead poisoning."
"If I had my vaccine I'd be vaccinating them right now," said Horovitz, saying he does not know why some hospitals were able to get their supplies of swine flu vaccine sooner, calling it "a mystery to me."
"I'd just like everyone who has high risk patients to have their vaccine, and certainly the seasonal flu vaccine is a good idea for everyone now, if there's any left," he said.
Despite protective effects of seasonal flu vaccine, it remains unclear if it has any effect in protecting people from H1N1, because the strains are so different.
Ultimately, however, swine flu may have a lower death toll because of the attention it has brought to the ways flu spreads.
"I suspect that the death rate will be lower than the seasonal influenza rate," said James. "Every effort is being made both socially and medically to limit the spread of the disease and those actions have been effective. We have never fielded such a response to influenza with vaccine, antivirals and social interventions such as covering your cough, washing your hands, staying home if you are sick so effectively."
ABC's Dan Childs contributed reporting.