MONDAY, May 11 (HealthDay News) -- The swine flu epidemic does have pandemic potential and is likely to be comparable to other 20th century pandemics, at least in terms of its spread, a new analysis concludes.

The report also suggests that the true number of -- largely unreported --swine flu infections in Mexico, the outbreak's epicenter, possibly had already reached 32,000 by the end of April. The World Health Organization's official tally for Mexico currently stands at 1,626 confirmed cases.

The situation could be similar in the United States. During a Monday afternoon news conference, Dr. Anne Schuchat, interim deputy director for science and public health programs at the U.S. Centers for Disease Control and Prevention, said that the 2,618 confirmed cases in the United States are likely just the tip of the iceberg. Many people who become ill don't seek medical attention and are never tested for this strain of flu, so "the numbers we are reporting are a minority of the actual infections that are occurring in the country," she said.

The authors of the study, released online Monday in the journal Science, estimated that the current H1N1 swine flu outbreak is likely to wreak less havoc than the 1918 Spanish flu pandemic that killed more than 500,000 Americans.

Instead, it may prove similar to the much less lethal 1957 pandemic of Asian flu, which killed about 70,000 people, according to U.S. government statistics.

For reference, about 36,000 people die in a typical flu season.

However, the authors are basing their conclusions mainly on infection rates, not on severity of the disease or number of deaths, added Dr. Ghinwa Dumyati, an associate professor of medicine, division of infectious diseases at the University of Rochester Medical Center.

"Not every pandemic is severe, and that's the issue," she said. "Severity does not depend on the number of people infected but on the fatality ratio."

Another expert agreed. "The most important unknown is the clinical severity of the illness, although the accumulating evidence is that the severity is no worse than that of the seasonal flu," said Dr. Christopher Crnich, an assistant professor of medicine in the division of infectious disease at the University of Wisconsin School of Medicine and Public Health. However, "no mathematical model is going to be able to predict [severity]," Crnich added.