By Elizabeth Cohen
Senior Medical Correspondent

So is the swine flu outbreak showing any signs of waning in the United States? Not according to the US Centers for Disease Control. “I believe we are just on the upswing here,” the CDC’s Dr. Anne Schuchat said in a press conference Sunday. “I do expect more cases, more severe cases, and I do expect more deaths.”

This is in contrast to what’s happening in Mexico, where the World Health Organization declared Sunday that the outbreak “is in its declining phase.”

What accounts for the difference? Time, according to Schuchat. The outbreak started in Mexico, and so it’s further along there than in the rest of the world. It’s not entirely clear when H1N1 infections started showing up in Mexico, but health officials there early Monday reported 568 cases and 22 fatalities linked to the flu, with the most active period of infections between April 23 and April 28. In fact, as a result, Mexico lowered its health alert from red or ‘high’ to orange or ‘elevated’. The United States has reported 226 confirmed cases in 30 states, including one death – a Mexican toddler visiting relatives in Texas.

No matter what happens this spring with H1N1, it’s important to remember this: flu outbreaks come in waves. So when it goes away this spring, it could come back in the fall. “In 1918, that pandemic started out as a very mild case of disease in the spring,” says Grogry Hartl, a spokesman for the WHO. “[The virus] almost completely disappeared over the summer, only to reappear in the autumn of 1918 with the vengeance which we all know. So even though we might be only seeing mild cases now, we cannot say what will happen in the future.”

Whether swine flu will come back in the fall “with a vengeance” is open to debate. “I would assume that it would be much worse in the fall,” says Dr. W. Paul Glezen, chief epidemiologist at Baylor College of Medicine’s Influenza Research Center, who based his assessment on how the flu virus behaved in the 1918 and 1957 outbreaks.

But Dr. Peter Palese, chair of the department of microbiology at the Mount Sinai School of Medicine in New York City, disagrees. “The swine virus may pter out completely and not return next winter,” he says. “I would be very skeptical making any prdictions as the to recurrence in the next winter. There is no good scientific evidence to suggest that this will happen.”

By the way, last week on Tony’s show, he asked what people think of Dr. Richard Besser, the acting director of the CDC; you’ve seen him on television multiple times talking about swine flu. I told Tony I’d ask his question on my Twitter page. The answer: people seem to love him. Here are a few examples:

– “His calm in the swell of this flu storm is impressive. Professional, personable, and clear in his reports. 2 thumbs up!” – farragounveiled

– “He looks and sounds very confident , educated and informed. That's what we need right now.” – medisort

– “He is completely capable and informative without causing panic. I'm confident he would do very well as Director of CDC.” – davidsbays

– “Besser is doing an excellent job. Perhaps he should be running TARP & TALF too?” – wonkguy

– “He did a great job. He was upfront & to the point. And he formed full sentences, so it's another step up.” – AshleyBartolome