Are there roughly 200 swine flu cases in Canada? Or about 1,800 cases in the United States? Or nearly 2,400 cases globally?
Do the numbers really matter?
With the new swine flu virus spreading quickly through many parts of North America and beyond, firm numbers of cases have less and less relevancy to public health efforts to respond to the outbreak, experts say.
While good estimates of the scope of disease activity are important in the early days of an outbreak, once a bug like this new H1N1 virus is spreading in a community, putting a figure on how many people are actually sick is, well, a guessing game.
"This counting of cases is some kind of 'folie a deux' or maybe 'folie a trois' that happens between politicians, public health people and the media," influenza expert Dr. Allison McGeer says, using a French phrase that means "madness shared by two" (or three).
"In an outbreak, you need to know whether it's going up or down. You need to know where you're going. But somehow - and I don't fully understand the source or the psychology of this - somehow we've evolved into: You have to have numbers."
"The result is people spend an unbelievable amount of time worrying about what the numbers are."
Trying to keep firm counts is especially futile with influenza, which is one of those tip-of-the-iceberg diseases. The vast majority of infected people never seek a doctor's help; and most doctors, in Canada at any rate, do not test for influenza.
That said, given the high level of public awareness about swine flu, more of the iceberg may be poking above the surface these days.
"People are getting tested that in a regular flu season ... wouldn't bother going to their doctor because they didn't have a travel history and ... if they did go to the doctor, would not necessarily have had a (diagnostic) swab," says Dr. David Butler-Jones, Canada's chief public health officer.
"We don't have any evidence to say that for sure, but that's likely."
While we're still counting, Canada has reported 214 cases in nine provinces.
In the United States, where authorities reported Thursday they have 1,823 confirmed and probable cases in 44 states, a move toward qualitative rather than quantitative descriptions of the scope of the outbreak is on the horizon.
"At some point, reporting on individual cases no longer has value from a public health perspective," says Dr. Richard Besser, acting head of the U.S. Centers for Disease Control. "But knowing where in the country we're seeing large amounts of flu activity does remain important."
Besser says the CDC will soon move to the type of reporting language it uses for seasonal flu, describing H1N1 swine flu activity in terms like "widespread," "localized" or "isolated."
Once transmission is happening in communities a case count "doesn't become as useful as being able to talk about widespread activity in a given place, limited activity, isolated activity. The kinds of terms that we've used in seasonal flu," Besser says.
Part of the issue is how much testing is being done and how quickly tests are being processed. As more laboratories take possession of the kits needed to test for this virus, case counts spike.
The virus is still spreading, so some of that rise in cases represents new infections. But some represent infections that have already occurred but for which testing is only now being done.
Besser uses an anecdote to explain the testing phenomenon. "Yesterday we had a visit from the mayor of New York who said: 'You want 200 more cases? Let me know and we'll test 200 more people."
Knowing where the virus is present and spreading is important, and that's where counting helps at the start of an outbreak. It also helps to show if cases are growing or if transmission is petering out.
But after a point, it makes no sense to jam up laboratories doing multiple tests that confirm the obvious - the virus is here.
Butler-Jones says at some point soon, Canada may pull back on testing in some places. "I think we're close."
"We'd like to be able to have some confidence that things are really diminishing," he says. "And so if you're still picking up new cases, then it may or may not be. But if you're doing testing and you're not finding it, then you're more confident that it is diminishing."
McGeer, who is head of infection control at Toronto's Mount Sinai Hospital, says when she teaches she tells medical students the blunt facts of the numbers game.
"Every day you have to have a number for public consumption. No matter what you do, that number will not be right, for just an innumerable number of reasons," she explains.
"It's got to be close, but it's never going to be perfect. And it really doesn't matter. It's just to tell people whether we're going up or down and give them a rough idea of (by) how much. ..."
"Is it getting worse? Is it getting better? Is it getting a lot worse? Or a lot better? Those are the questions. And if you answer those questions, that's what you need from the number."
