“Outbreak” or “Epidemic”- What Defines it and Who Decides it?

Aug 18, 2017

At PathSensors, we committed to rapid, reliable pathogen detection and diagnostics for diseases, pathogens and toxins and often, we are a response to these terms “epidemic” or “outbreak”.  In fact, our CANARY® technology was created in response to an outbreak of anthrax attacks. But what do these words mean?

Many of us hear this word in the media frequently when referring to an outbreak of the flu or a Zika epidemic. Or maybe you’re just thinking of the Morgan Freeman in the 1998 Drama Thriller “Outbreak”. For the most part, these terms are vague. We are going to break them down to better understand these concepts and how we should react accordingly.

So, let’s start with the basics. According to the CDC, the amount of disease that is normally present in a community is referred to as the baseline or “endemic” level of disease, while this might not be the ideal level of “0”, it is the observed level of disease in the community. And this level will NOT deplete the pool of susceptible people if there is no intervention, so for example: this might mean that while there are a few cases in the community it will not significantly impact population or the community.

However, when this expected level of disease rises above the expected level very suddenly this is considered an epidemic. Outbreak also means a sudden rise about the expected level of cases but this is used in a limited geographic region.

  Outbreaks or epidemics are usually a result of several factors. One factor could be an increase in the amount of the pathogen present or its harmfulness has increased. It may be the recent introduction of this pathogen into a new setting. A change in the susceptibility of the hosts or increased exposure or the hosts through new portals of entry (ways that the pathogen or sickness can enter the host).

For every disease, defining these terms is a bit different, as there are epidemic thresholds for only some diseases. That means that while there might be 50% attack rate from flu, but with a low mortality rate (7%) that’s not nearly as concerning or considered an epidemic as a Smallpox with a 30% mortality rate.

Now the question becomes, how can media use these two terms? The answer is typically in whatever manner they’d like. While the appropriate usage of epidemic, outbreak and pandemic are based on thresholds over geographical areas and populations, headlines like “Baseline number of cases of flu in Utah” don’t garner nearly as much attention as “Utah Flu Outbreak” (for example).

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