"It could just represent the results of improved surveillance by the CDC -- they have stepped up flu surveillance -- or it could be a low level transmission of a newly emerging strain," he said. "Or [it] could possibly be the start of a new epidemic."
Despite the prevailing concern over the swine flu cases, other infectious disease experts believe that it is not quite time to consider this virus a major public health threat.
First of all, it would not be the first time the country has encountered a pandemic. In the 20th century alone there were three pandemics of influenza.
The worst was the 1918 influenza pandemic, which caused at least 675,000 U.S. deaths and up to 50 million deaths worldwide. The 1957 influenza pandemic caused at least 70,000 U.S. deaths and 1 million to 2 million deaths worldwide, while the 1968 influenza pandemic caused about 34,000 U.S. deaths and 700,000 deaths worldwide -- only about as many deaths as a normal flu season.
Flu experts also point out that several conditions must all be satisfied at once for a full-blown pandemic to occur.
"[There] is a very low probability [that this is will be a] high-consequence scenario," said Dr. Peter Katona, associate professor of clinical medicine at The David Geffen School of Medicine at UCLA. "The potential is there to do great harm, but many factors -- season of the year, level of hygiene, robustness of the virus -- have to come together for the 'perfect storm' to happen."
Moreover, some experts pointed out that the increased diagnosis of these cases of swine influenza in humans was an accidental result of increased CDC flu surveillance. Therefore, there was no cause for concern about the new influenza strain before the CDC accidentally identified it.
"It is of note that the two cases in California were 'accidental' findings, as both infected children were treated in facilities that carried out clinical studies," said Nicole Baumgarth, chair of the graduate group in Immunology at the University of California at Davis. "Identification of the virus was done therefore by 'looking harder' rather than because of clear suspicion of influenza. ... Increased surveillance will result in increased diagnosis."
Another advantage that health officials enjoy is the fact that while the virus appears to be resistant to at least two weapons in the antiviral arsenal -- amantadine and rimantadine -- it is still susceptible to the popular flu drugs oseltamivir (Tamiflu) and zanamivir (Relenza). Besser said that scientists are also already starting work on a preliminary vaccine for the illness.
And he said the country is prepared to deal with the threat of a pandemic-level virus should the situation escalate.
"The level of planning that has taken place in this country is unprecedented," he said, adding that preparations in recent years would allow U.S. health officials to respond to a pandemic threat far more effectively than in the past.
Mexico, meanwhile, is taking no chances. A government order Friday closed Mexico City private and public schools, from pre-school through university level. The Associated Press also reported that Friday afternoon, the country's government closed museums, libraries and state-run theaters in Mexico City in an effort to curb the outbreak.