Citizens around the world are concerned about the swine flu (H1N1) virus, which has been most insidious in Mexico but is also affecting travelers in the U.S., Canada, Europe, New Zealand, and a growing number of nations. As of May 11, 3 U.S. deaths and upwards of 4,700 cases had been confirmed, with hundreds more suspected; as shown on Google
and Rhiza Lab’s Swine Flu incidence map.
Amid all the hype, assessing the real risks posed by the global spread of the disease can be daunting. Terms like “outbreak,” “epidemic,” and “pandemic” are often used liberally and interchangeably, infecting listeners with fear and confusion. Luckily, My Wonderful World is here to the rescue! The distinctions among these terms, and their implications, are–you guessed it–geographic.
Here’s a quick primer: An outbreak occurs when the reported cases of a disease are greater than the levels predicted for a given area or period of time. That means that if one person is predicted to get the flu in your town, and two become ill, it’s an outbreak! Outbreaks are usually, but not always, limited in geographic scale. The current swine influenza was considered to have reached outbreak status in April as a result of growing numbers of cases in Mexico.
Technically, the term epidemic can be used synonymously with outbreak, but it typically refers to a larger-scale incident affecting greater numbers of people in a more expansive geographic area. Confirmed reports of swine flu in the United States and Canada signaled an epidemic.
A pandemic is an epidemic that has reached global proportions. The World Health Organization recognizes six stages or “phases” in the development of pandemic flu (these stages largely replace use of the terms outbreak and epidemic). The phases are categorized according to several factors including (1) virus presence in animals and/or humans, (2) rate of transmission, (3) geographic extent of the disease and (4) response recommendations.
Here’s a phase-by-phase breakdown of the growth of a global pandemic:
In phases 1 and 2, a new strain of flu emerges in animals (usually
domesticated pigs, birds, or horses [in phase 1]) and is transmitted to
small numbers of humans (phase 2).
Phases 3, 4 and 5 follow
initial transmission from animals to humans, up through levels of
outbreak, epidemic, and imminent pandemic. The escalation of flu
status from levels 3 to 6 is primarily defined in terms of geography.
Some more specifics:
3 is characterized by small, localized clusters of disease which grow
to outbreak status by Phase 4. In Phase 5, larger epidemic clusters
develop in at least two countries within a single world region,
signaling an imminent pandemic. When the disease spreads to a second
world region, it is classified as a Phase 6 global pandemic. After the
pandemic has reached this peak phase, it is likely to taper off,
although the threat of additional waves exists over subsequent months
during the post-peak and post-pandemic phases.
Clear as mud,
right? Even after meticulously reading the descriptions, I admit I’m
still a little perplexed by the phase delineations. As far as I know,
swine flu has not yet been elevated
to Phase 6 status, despite reported cases in well more than three
countries and two regions. Is this because the incidents have been
linked primarily to isolated instances of travel, and not more
“organic” forms of trans-boundary transmission? Or perhaps factors of
severity and mortality are trumping markers of geographic diffusion?
Hopefully, there is a public health official, epidemiologist, or
medical geographer who can lend some insight!
In the meantime, here are some resources to continue exploring:
Google Flu Tracking
1. FluTracker Incidence Map
Global trends for “swine flu” searches
2. Worldwide searches
Do any of the countries on the “top 10” search list surprise you?
3. U.S. vs. U.K. vs. Mexico vs. Japan searches
Why do you think there are so few searches for swine flu in Mexico compared with the United States? Look at the state-by-state comparisons for the United States. Does it
surprise you that there were more searches for swine flu in
Maine than in Texas?
Swine flu is not caused by eating pork!
Sarah for My Wonderful World