U.S. Declares Public Health Emergency, Confirms 20 Cases Around the Country

Dr. Lewis Goldfrank, professor and chairman of the Department of Emergency Medicine at Bellevue Hospital in New York City said that though no cases have been detected in his emergency department yet, any patient who comes in with a cough and a fever or a rash and a fever is isolated for a nasal swab to detect influenza -- a test that takes about an hour.

The possible outbreak in the New York area suggests the measures may be warranted.

A Delay in Action?

Another question that remains is whether health agencies reacted quickly enough to the initial reports of swine infections in Mexico, first reported in mid-March.

"I think that the laboratory testing capabilities for this type of virus were not fully in place and this accounts for some of the delay," said Dr. Pascal James Imperato, dean of the Graduate Program in Public Health at SUNY Downstate Medical Center in Brooklyn, N.Y. "They were not routinely testing for this type of influenza virus."

Still, other infectious disease experts said that there should have been quicker action.

"I concur that the 'one-month lag' between case identification and reporting was too long," said Ed Hsu, associate professor of Public Health Informatics at the University of Texas School of Health Information Sciences and School of Public Health. "[It is a] good thing that the CDC now decides to have a daily briefing on the swine flu, but it will still need to bring the transparency of reporting in other high-risk countries up to speed on this."

And despite the actions by the World Health Organization with regard to the swine flu outbreaks, no decision has yet been made to increase the pandemic threat level from its current status of phase 3 to phase 4 on the six-point scale. A virus isn't considered to be pandemic until it reaches phase 6.

WHO did announce, however, that it has sent a team of experts to Mexico to further study the outbreaks.

Still Too Early to Worry?

Despite the action being taken by national and international health organizations, some infectious disease experts say it is far too early to fear the worst -- a global flu pandemic.

"The current swine flu only marginally meets only one of three of pandemic tests: effective person-to-person transmission," Hsu said, adding that the other tests -- susceptibility and no natural immunity or vaccine -- remain to be satisfied.

Hsu further noted that compared to the H5N1 strain of the avian flu virus -- commonly known as bird flu -- the current H1N1 swine flu strain is still a relative lightweight. Since 2003, he said, bird flu has garnered a 60 percent case fatality rate, and it never attained pandemic status. Meanwhile, the current swine flu strain still has fewer than 1,000 reported cases and only about 60 fatalities to its name.

"If not [a pandemic] then, why now?" he asked.

"I think its still early to say," said Nathan Wolfe of Global Virus Forecasting Initiative. "We're still early on in an outbreak like this. One of our main objectives is to try to figure out case mortality rate, what percentage of individuals that it affects does it kill. But what's really a concern is that this virus is clearly spreading from human to human, which is at the point where we become really interested and focus on understanding that."

Swine Flu Vaccine Would Be Months in Making

But if more cases did arise, Schaffner said that a vaccine for the illness would not be available for months.

"It would be an Olympic sprint for vaccine manufacturers, starting today" to have a usable vaccine ready even by October, he said.

"If this is a virus that is sufficiently new -- and that has not been entirely determined yet -- we may need two doses of the vaccine to get protection," Schaffner said. "That, of course, would put additional strain on the vaccine production and delivery services."

ABC News' Dan Childs and Matt Hosford contributed to this report.