As the swine flu crisis threatens to become a global pandemic, health experts are asking whether the health system in Mexico, where the virus originated, is up to dealing with the outbreak and whether an earlier response might have prevented its worldwide spread.

Both the World Health Organization and the U.S. Centers for Disease Control and Prevention have sent teams into Mexico after government officials there requested their assistance.

As of Tuesday morning, the virus was suspected to have caused 152 deaths in Mexico. But with thousands more patients yet to be tested, observers warn the worst may be yet to come.

"Mexico does not have the kind of measures in place we have in this country," said Dr. Len Horovitz, a pulmonary specialist at Lenox Hill Hospital in New York. "This virus has been circulating since sometime in March and could involve thousands or hundreds of thousands of people."

Reports indicate that hospitals around Mexico started seeing a rise in patients complaining of respiratory distress as early as the middle of last month.

But the WHO wasn't made aware of the situation until a month later. Within a week people in Mexico were dying of flu-like symptoms and two children in California were diagnosed with a new strain of swine flu, believed to be the same strain circulating through Mexico.

Dr. Keiji Fukuda, an assistant director general with the WHO, defended Mexican health officials in a news conference on Sunday, pointing out that the country — which has been hard hit by the global recession and is devoting many of its resources to its war against drug cartels — was in the middle of flu season when the increase in patient load began.

"This is not the kind of activity that we would typically ask a country to report to WHO as being suspicious," he said. "I think they took some very prudent actions, which was to initiate investigations on their own and try to analyze the situation, figure out what (was) going on (as) they collected samples."

As it stands now, Mexican public health officials have to send samples from suspected patients to the CDC center in Atlanta to confirm whether they are infected with the new swine flu virus, said a WHO spokeswoman.

Dr. Carlos Del Rio, a medical professor at Emory University’s Infectious Disease Division, just returned from a four-day trip with public health officials to Mexico City and said he was impressed with the level of organization there.

"I think they're dealing with a lot of cases, but the response has been pretty good," Del Rio said. "Overall, I was quite impressed."

But other health officials have been far more critical.

Francoise Weber, director general of France's Sanitary Surveillance Institute, said Mexico should have realized it had a flu outbreak sooner.

And the director of the Mexican Epidemiological Organization, Oswaldo Medina, told the newspaper Reforma that Mexico’s health care system was ill-equipped to handle the demands of a flu outbreak of this magnitude.

"Identification of the disease comes late, the response is delayed and the diseases cannot be controlled," Medina said.

Mexico's president, Felipe Calderon, ordered all schools closed indefinitely over the weekend and forbade any public gatherings until the outbreak is brought under control.

When that will be is anyone's guess.

Doctors are still struggling to confirm that the 152 patients in Mexico believed to have died from swine flu did in fact have the virus. And there are questions about why the outbreak in Mexico is so different from what other countries are seeing.

"Why did the Mexican cases have such a high mortality? Are the strains from Mexico and New York the same?" said Dr. Peter Katona, a UCLA medical professor who used to work with the CDC. "We're going to be looking for explanations, and we should have some answers in the next few days."

But as countries around the world clamp down on their borders, some American lawmakers are asking why more isn't being done here at home.

Rep. Eric Massa, D-N.Y., has called for the U.S.-Mexico border to be closed in order to curb the spread of the virus.

"I'm glad that the White House has issued a travel advisory and is conducting passive screening at the border, but I think we should consider stronger measures at the border. I am in favor of using all tools available to reduce the spread of swine flu," he said in a press release.

On Monday afternoon the WHO increased the pandemic alert to level 4, two steps below a full-blown pandemic. But it said it was too late to contain the outbreak by shutting down borders.

"The current focus of efforts should be on mitigation rather than trying to contain the spread of this virus," Fukuda said. "This virus has already spread quite far, and at this time containment is not a feasible operation."