TUESDAY, April 28 (HealthDay News) -- As the death toll from swine flu in Mexico rises and new cases appear in the United States and elsewhere, it's easy to get caught up in a sense of mounting dread.
But experts in influenza and infectious disease say the exact level of danger from the virus is still far from certain.
"This is something of concern [but] I think we should hold back on calling it a real threat," said David Topham, co-director of the New York Influenza Center of Excellence, part of the University of Rochester Medical Center. "We always have to take these things seriously, but we have a very good system in place to respond."
Another expert agreed.
"The gravity of the situation will not be clear for a few more days till we find the extent of the cases and the number of countries involved and explain why we haven't had any deaths in the U.S," said Dr. Scott R. Lillibridge, a professor with the Texas A&M Health Science Center School of Rural Public Health in Houston and executive director of the university's National Center for Emergency Medical Preparedness and Response.
The real verdict on just how dangerous this outbreak might be will hinge at least partly on seeing how the disease spreads in the United States, along with expected announcements from the World Health Organization as to how many other countries are affected, the experts said.
So, as can happen in these situations, "the panic is a little bit undue," said Dr. Len Horovitz, a pulmonary specialist at Lenox Hill Hospital in New York City. "There are many facts that we don't know."
Looming large among the unknowns: Why is the virus causing more severe illness in Mexico than in the United States? Why have the only deaths reported been in Mexico? Why is mortality concentrated among young, healthy adults? Will the swine flu acquire more lethality as time goes on? And will the virus have a seasonality to it, like the "regular" flu?
Most of these questions have no solid answers -- at least not yet -- but there are some intriguing possibilities.
The death rate from the swine flu in Mexico (149 by late Monday) hovers at about 7 percent of the more than 1,900 so far thought to be infected -- a percentage that's alarmingly higher than the 1918 Spanish flu pandemic, which is thought to have killed about 2.5 percent of infected persons.
But this early in the outbreak, no one really knows the true extent of the Mexican outbreak, the experts noted, so that 7 percent figure might well be too high.
"We don't know the total number of people exposed," Topham said. "It could be many more people exposed, so we're only hearing about the ones who got really sick and died," he explained.
It's also not clear if all the deaths attributable to swine flu were actually caused by the virus.
"The strain in the U.S. seems to be the same as in Mexico, but in Mexico we've not had confirmation of all those hospitalizations or deaths," Lillibridge said. "We're comparing apples and oranges."
And to put things into perspective, even with the death toll in Mexico, the swine flu does not appear to be as dangerous as SARS (Severe Acute Respiratory Syndrome), which appeared seemingly out of nowhere in 2003.
"SARS had high human-to-human transmission, there was a high death rate and no treatment," Horovitz noted. With the swine flu outbreak, "we're not talking about anything like that," he said.
In fact, all 40 U.S. cases so far have been mild or the patients have recovered, the U.S. Centers for Disease Control and Prevention reported.
And, in absolute numbers, the death toll is still nowhere near the roughly 35,000 lives snatched each year by the regular "garden variety" seasonal flu, Horovitz pointed out.
But could this outbreak morph into something more alarming?
"We just don't know yet," said Dr. Mark Metersky, spokesman for the American College of Chest Physicians and a professor of pulmonary and critical care medicine at the University of Connecticut School of Medicine in Farmington. "It's early in the outbreak."
Metersky pointed to a 1976 outbreak of swine flu that erupted at Fort Dix, N.J., caused a scare, but then quickly petered out with one death.
Perhaps the most disturbing trend in the Mexican outbreak is the fact that it is primarily young adults who are dying. That's not typical, experts said.
"It is usually people who are weakest, at extremes of age, very young and very old who succumb to influenza and this is a little bit scary because this is a pattern we saw in the [flu] pandemic in 1918," Metersky said.
On the upside, there's a good chance that swine flu may not stick around for long in northern climes, at least not this year. "This will probably have seasonality similar to the one of the regular flu," Topham said. He pointed out, however, that the regular winter flu is never quite gone, because as it wanes from the Northern Hemisphere, it re-establishes in the Southern one.
U.S. health officials declared a public health emergency Sunday in response to the swine flu outbreak, and the number of confirmed cases nationwide had doubled by Monday to 40. The 20 new cases all came from the New York City high school that had previously reported eight cases of the infectious disease.
Some of the U.S. cases, all of which so far have been mild, involved people who had recently returned from trips to Mexico.
Meanwhile, in Mexico, believed to be the source of the outbreak, authorities continued to take dramatic steps over the weekend -- including suspending public gatherings -- to try to contain the swine flu outbreak.
U.S. health officials have reported that they have 50 million doses of the antiviral flu medication Tamiflu. A quarter of those doses were being released to states, if needed.
"The benefits of antivirals are twofold," Lillibridge explained. "In treatment, to shorten the illness and promote recovery at an earlier time and to prevent complications. Second, it can be used in prevention. If you have been exposed to someone who has swine flu, [the drugs are] 70 to 90 percent effective if taken early enough."
Steps have also been taken to perhaps devise a vaccine against this strain of swine flu.
Swine flu is a respiratory disease of pigs caused by type A influenza. Swine flu does not normally infect humans. However, human infections do occur, usually after exposure to pigs. Symptoms resemble those of the regular flu, including sore throat, coughing and fever. The strain of swine flu circulating in North America appears to be a combination of pig, bird, and human flu strains, experts say.
What You Can Do
For right now and for the next few days, the only people who need to worry about infection are those who have been in Mexico or those who have been around people who have visited that country, said Dr. Mark Metersky, a spokesman for the American College of Chest Physicians.
Experts say precautions against catching swine flu are similar to those recommended for the regular flu, including the following:
There's more on swine flu at the U.S. Centers for Disease Control and Prevention.
SOURCES: David Topham, Ph.D., co-director, New York Influenza Center of Excellence, and associate professor, microbiology and immunology, University of Rochester Medical Center, New York; Len Horovitz, M.D., pulmonary expert, Lenox Hill Hospital, New York City; Mark Metersky, M.D., spokesman, American College of Chest Physicians, and professor, pulmonary and critical care medicine, University of Connecticut School of Medicine, Farmington; Scott R. Lillibridge, M.D., professor, Texas A&M Health Science Center School of Rural Public Health, Houston, and executive director, National Center for Emergency Medical Preparedness and Response