The tally of swine flu cases worldwide is only a small part of the ongoing global effort to understand the virus, health officials said Tuesday.
The number of confirmed cases in the United States stood at 68 as of midday Tuesday, including 17 new cases in New York state and the first case in Indiana.
Germany confirmed its first cases of swine flu on Wednesday. A small number of cases also have been reported in Israel, New Zealand, Scotland, Canada and Spain.
But the tally is only a small part of the global effort to battle the flu. This is a disease that is common among pigs, but only occasionally spreads to people, where it causes flulike symptoms. A new variation of this virus has been able to spread person-to-person. What happens next depends on biology.
Dr. Keiji Fukuda of the World Health Organization said at a news conference Tuesday that the virus has demonstrated that it can move within a confined group of individuals — in particular, it spread from New York schoolchildren who visited Mexico during spring break to classmates back home. Fukuda said there are plenty of examples of diseases that can spread easily within tightknit groups, such as schools, day-care centers and retirement homes.
The real question, though, is whether the new swine flu virus can spread readily beyond these confined groups. If the virus doesn't spread easily, the current outbreak will quickly burn itself out. If it can get a foothold in a community, it has the potential to become a pandemic.
Health officials are therefore trying to identify and investigate any and all cases of swine flu, to understand how this disease is behaving right now.
If it turns out that the virus can spread readily throughout a community, the next question is how serious it will be. British health officials have suggested that the flu could be a "mild pandemic" — a widespread disease that isn't especially dangerous.
One sign this could be the case is that most cases of swine flu outside of Mexico have been mild, usually not even requiring hospitalization. It helps that anti-flu medicines are effective at reducing the severity of this strain of swine flu.
On the other hand, dozens of cases in Mexico have resulted in severe pneumonia. The World Health Organization recognizes seven confirmed deaths in Mexico, though Mexican health officials suggest that the actual number of deaths there exceeds 150.
Health officials don't understand why the disease has been so serious in Mexico and so mild elsewhere — particularly because as far as they can determine, people are infected with exactly the same virus. That's another key question they are trying to answer quickly.
"One of the lessons that history has shown us is pandemics can range from being relatively mild to being extremely severe," Fukuda said at the news conference. He added that it's too early to say where this one is heading.
"The worst pandemic of the 20th century occurred in 1918, and it also started out as relatively mild. The spread of illness that wasn't much noticed, and then in the fall time it became a very severe pandemic," Fukuda said, adding that it was "one of the most severe infectious disease episodes ever recorded. So I think we have to be mindful and very respectful that influenza tends to move in ways that we cannot predict very easily."
One lesson from the flu epidemic of 1918 is that even if the current outbreak fizzles out, this strain of swine flu virus could still lurk quietly in the background and re-emerge next fall, when flu season returns. That's one reason the WHO is ramping up a six-month project to develop a vaccine against this current strain.
The other lesson is that vigilance helps a lot. Health scientists are on high alert for swine flu not because it's a current health emergency — it is not — but because if it becomes one, they will know the virus well enough to mount a vigorous defense.