Sept. 9, 2009 -- If you're wondering whether your sniffling co-worker's bout of flu is indeed the swine flu, then wonder no more.
Doctors across the nation are saying people who came down with the flu this summer probably had the new swine flu (H1N1) strain.
"In the U.S., all the flu that is circulating now is the H1N1 virus," said ABC News Senior Health and Medical Editor Dr. Richard Besser on "Good Morning America" Wednesday. "If you've had the flu; you've had the swine flu."
Since the U.S. Centers for Disease Control and Prevention first started tracking the H1N1 strain in mid-April, the agency has counted 9,079 hospitalizations because of it.
Swine flu also accounted for about 96 percent of all tested flu strains in the past week, according to the CDC.
Those statistics prompted a number of infectious disease experts across the country to echo Besser's assumption.
"Most people recently stricken by flu are highly likely to have had swine flu," said Dr. James Wilde, associate professor of pediatrics at the Medical College of Georgia in Augusta.
Track the H1N1 (Swine Flu) Virus with the CDC's Weekly Updates
Besser, who is former acting director of the CDC, and other doctors say there are plenty of reasons why the public should not worry more about swine flu than the typical seasonal flu.
Reason One: The Swine Flu's Not So Bad
The CDC estimates that 1 million people in the U.S. have had swine flu so far, and of those infected, the government has documented 593 deaths.
"This is a relatively low death rate when compared with seasonal flu," said Wilde. "The public is still edgy about swine flu because of the appropriate precautions taken in May before we fully understood the level of danger."
The swine flu strain has also shown it does not often cause serious symptoms.
"What we're seeing in terms of illness is relatively mild. So unless you're in one of the high-risk groups, you can treat this with rest, fluids, chicken soup and staying away from other people to avoid spreading it to them. That, for the most part, is very effective," said Besser.
When doctors track the spread of a virus, they look at how dangerous it appears at the start. But they also look to see if the virus is mutating into something stronger or weaker.
"Since there are no reports of mutation of the virus to a more lethal strain, the public should take comfort in the fact that in the overwhelming majority of cases (those people that are not high risk) this virus causes a relatively mild, self-limited illness," said Dr. Len Horovitz, a pulmonary specialist at Lenox Hill Hospital in New York City.
Reason Two: Swine Flu Survivors May Be Immune to Reinfection
With a few months of investigation under their belt, immunologists are saying that the swine flu comes with more good news: it appears people who get sick with swine flu may not become sick from the same strain again.
What's more, even people who were sick in the past with a slightly different virus may have some protection against the current strain.
"Having H1N1 now would confer immunity in the future -- this seems to be why people born before 1957 have relative immunity," said Horovitz.
What to do About Swine Flu
Dr. John Treanor, a professor of medicine in the infectious diseases unit of the University of Rochester Medical Center, agreed.
"Most likely, if you had (the new) H1N1 in the spring, you would be relatively protected this fall, since the virus really hasn't changed much," said Treanor.
Doctors Still Cautious
But doctors warn that not everyone who had the sniffles this year should feel immune to swine flu. You may think you had the flu, but it could be a cold virus or a bacterial infection.
"Because other viral infections can mimic the flu, unless you are sure and a test was positive, you should be vaccinated, particularly if you are in one of the priority groups that is at higher risk of severe infection," said Dr. Christopher A. Ohl, associate professor at the Wake Forest University School of Medicine in Winston-Salem, N.C .
And doctors say there is no guarantee that the swine flu virus will not change in the future.
"Over subsequent outbreaks, as the population begins to build up immunity, the virus will likely begin to drift in the same way that seasonal viruses do, and the immunity you gained from your first infection would not be as effective," said Treanor.
So we've had it easy so far, but doctors caution that the flu is the flu -- and hundreds of people die from influenza every year. Doctors say they hope the public doesn't become lax about flu care this winter.
"It is important to take all the precautions that have been talked about since late April: cover your cough/sneeze; good hand hygiene, stay at home if ill and, if having shortness of breath or severe symptoms, go to the doctor," said Carlos de Rio, a professor of medicine and infectious diseases at Emory University in Atlanta, Ga.
"Also, people should get their seasonal influenza vaccination now," he added.