On Sunday, the Department of Homeland Security held a press conference to announce that the swine flu outbreak that has spread from Mexico to the US and other countries was being declared an official public health emergency. Also over the weekend, the World Health Organization convened a meeting of its Emergency Committee to evaluate the situation. Said Committee has determined that "the current situation constitutes a public health emergency of international concern." If this language sounds like dispensation to panic, it's worth stepping back and looking at what led to these declarations and what they mean in practical terms, as the implications of these decisions are far more mild than the language would suggest.

We'll start where the current version of the swine flu virus apparently did, in Mexico, where dozens have apparently died due to influenza. That may sound disturbing, but it's important to remember that most people with the flu evade any sort of public health surveillance—they feel awful for a few days, and then get on with their lives. As such, it's impossible to tell what the actual mortality rate among those infected with the virus is. Complicating this situation further is the fact that not all cases of flu-like symptoms are caused by the flu, and there may be other flu viruses circulating at the same time. These factors probably explain a number of the suspected cases in other countries that have turned out not to be cases of the swine flu.

By the time a sufficient number of serious cases had occurred in Mexico to alert the public health authorities, the virus was already in the process of spreading beyond its borders. Fortunately, the US Centers for Disease Control has a good relationship with its Mexican counterpart, and an extensive monitoring system is in place for the flu virus. The CDC, with the help of some alert medical professionals like a school nurse in New York City, has helped track this specific strain of swine flu as cases appeared in the US. Others have now been spotted elsewhere in North America and Europe, and there are suspected cases in Australia.

The tracking of the (now global) spread of this form of the flu is moving rapidly, so any numbers are likely to be out of date by the time they appear in the press. So far, most of these cases have occurred in people who have recently traveled to Mexico, but at this point, it's clear that the infected individuals have had enough contact with others that the virus is likely to have moved beyond that population unless it spreads poorly—and events in Mexico suggest that's not the case.

The CDC's monitoring has allowed a number of cases to be identified that might not have otherwise come to light, as very few of the US cases have wound up putting people in the hospital; so far, all have recovered. As the CDC's Acting Director Dr. Richard Besser put it, "In terms of detection, what we're seeing in this country is mild disease—things that would never have been detected if we weren't ramping up our surveillance." It's not clear whether this represents the typical course of the infection or whether some environmental or genetic factor enhanced the severity of some of the cases in Mexico.

Scary language masks practical steps

If none of that quite sounds like a "public health emergency" to you, you're not alone. Even the head of the Department of Homeland Security, Janet Napolitano, felt as much. "That sounds more severe than really it is," she said when announcing the emergency. "This is standard operating procedure and allows us to free up federal, state, and local agencies and their resources for prevention and mitigation." She pointed out that DHS had declared Obama's inauguration an emergency of similar severity, as it was the best way under department rules to provide the necessary security for the event.

Clearly, the number of direct parallels between the swine flu and the inauguration is pretty small, but Napolitano and Besser detailed a number of concrete steps that the emergency declaration would produce. Napolitano pointed out, for example, that the US has a strategic supply of modern antiviral drugs, primarily Tamiflu and Relenza, in a strategic national stockpile. A quarter of the full treatment courses, or over 10 million of them, were now being released for distribution, meaning that local hospitals should be assured of a basic supply even if there was a public run on the drugs.

Meanwhile, the CDC is taking a variety of practical steps. These include creating a seed stock of this specific virus so that work could progress rapidly on an immunization should the decision be made that one is needed. They're also working with Mexican public health authorities to expand the country's in-house testing capacity, allowing it to better track the dynamics of the outbreak.

Finally, it's giving the CDC to chance to highlight its basic information on the swine flu—you're very unlikely to get it from pork products, for example—and provide some basic (if obvious) public health advice: wash your hands often, and stay at home if you're not feeling well. The detailed information prepared by the CDC was posted online on Sunday.

Similarly, the World Health Organization's declaration led the organization to identify a number of areas where further research was needed regarding the behavior and spread of the virus. It has also called on national health organizations to increase monitoring and reporting so that it can be more carefully tracked.

So, the worrisome language is primarily due to standing rules that make these declarations necessary in order to fully mobilize the needed resources. Those resources will go to monitoring the dynamics of the spread of this virus, and putting the pieces in place to combat it if it develops into a serious public health concern. So far, indications are that it won't, as the cases outside of Mexico have been mild, and it's not clear that the Mexican fatalities are representative.

In trying to stay on top of the latest news, however, it's worthwhile noting something mentioned by the CDC's Besser, who said in reference to his group's website, "because of this speed in which things are progressing, you will at times find inconsistent information, and we're going to work really hard to make sure that that doesn't stay up for long." The same can almost certainly said for other media outlets, which are probably getting significant portions of their own information from the CDC in the first place.

Check back later this afternoon when we dive into a bit of the biology behind the flu virus.