Public health definition of "end of epidemic"?
March 11, 2016 11:22 AM   Subscribe

How does one come to define the end of an epidemic? Whether HIV or Ebola, smallpox or Zika, what are the accepted public health guidelines for defining the end of an epidemic/pandemic? I can't find the answer anywhere and hopefully you fine folks in public health can help.
posted by Sophie1 to Science & Nature (10 answers total) 1 user marked this as a favorite
 
For Ebola, the CDC says:
Criteria for declaring the end of the Ebola outbreak in Guinea, Liberia or Sierra Leone

Information note - Updated May 2015 (*)
Definition of "zero" Ebola cases

The outbreak of Ebola Virus Disease (EVD) will be considered ended in any one of the above countries after 42 days have passed since the last confirmed case has tested negative twice for the virus on blood samples (see Note 1 below). After the 42-day period has elapsed, each country should maintain a system of heightened surveillance for a further 90 days, and ensure ongoing EVD surveillance and notification thereafter. The end of the Ebola outbreak in the West African sub-region will be declared when the 42-day period has elapsed in the last affected country.
I suspect that "end" for any given epidemic is going to be disease-specific.
posted by rtha at 11:27 AM on March 11, 2016 [1 favorite]


Response by poster: There must be guidelines though, no?
posted by Sophie1 at 11:31 AM on March 11, 2016


In Ebola's case, they did it country by country. If I remember right, it was 2x the maximum incubation period - after 42 days of seeing no new confirmed cases, the outbreak is over.

It's different for things where there's a vaccine; the disease can be "eradicated" with a few people still coming down with it.

The whole point of an epidemic is that it's still getting transmitted between people, especially in the wild (like, you and a guy in the theatre, not you and the nurse who's treating you.) That's what public health people are worried about.
posted by SMPA at 11:33 AM on March 11, 2016 [1 favorite]


> There must be guidelines though, no?

I assume so, but I guess I'm not sure what level of specificity you're expecting (I am also not a public health expert, I just married into it). There are so many variables in e.g. transmissibility of a disease that I'm not sure how general guidelines could be and still be useful. For Ebola, they want 0 cases in [X] time period; for a disease that is less communicable and deadly, the guideline might be that [some cases above 0 but fewer than some threshold in [Y] time period].
posted by rtha at 11:46 AM on March 11, 2016 [1 favorite]


Response by poster: Basically, I'm looking for a scientific guideline as to how the World Health Organization determines what would be considered the end of an epidemic.
posted by Sophie1 at 11:50 AM on March 11, 2016


From WHO Guidelines for Preparedness and Response to Measles Outbreaks (.pdf): "Measles eradication is defined as the world-wide interruption of transmission of the virus, and represents the sum of successful elimination efforts in all countries and regions."

A possibly useful definition, related: "Zero reporting: Reporting of the absence of cases of a disease under surveillance; this ensures that participants have not merely forgotten to report."

Not a public health expert, but I hope you find what you need.
posted by MonkeyToes at 12:10 PM on March 11, 2016


You might find better answers if you can identify examples in which public health officials have declared that an epidemic was over. Ebola is relatively easy because there's an incubation period so if no one has gotten sick over a specific period of time, it's over, at least for the time being. For something like smallpox, I'd say that it was effectively over when the number of cases stopped spiking - if there are typically 100 cases a month, then there were 500 a month, then it was back to 100/month for several consecutive months.

Zika and HIV are more complicated because most people with those diseases don't know it, and if they don't know it, public health officials certainly don't know it.
posted by kat518 at 12:11 PM on March 11, 2016


WHO uses the term "outbreak" (not epidemic), which may help with your searching. For ebola they define it as having disrupted all the chains of transmission for the virus in a particular geographic area. (As someone notes above, 42 days after last known patient is negative, but they expect further resurgences as it's not known how long the virus can survive in the testes, for example.) It does vary by disease, depending upon the lifecycle and transmission pattern of the disease in question.

WHO also does its tracking of disease outbreaks primarily through national health organization statistics (such as the CDC), so CDC definitions/guidelines are likely to be helpful. You can sign up for outbreak alerts from the WHO if you happen to have an unhealthy obsession with disease outbreaks like, um, me. There's an RSS feed. For specifics, you probably want the International Health Regulations which has the general rules and guidelines, and its emergency committees, which help develop specific disease response guidelines as they arise. (polio, zika)

No expertise, just a morbid fascination with zoonotic diseases that leads me to read a lot of books about them. In my morbid-fascination experience, the WHO is very, very bureaucratic and very focused on serving their primary customers, which are national health organizations and NGOs, so their public communications can be not-great. The CDC will often have more complete and clear information on outbreaks for the average citizen who's just curious.
posted by Eyebrows McGee at 12:27 PM on March 11, 2016 [2 favorites]


Best answer: To give you a quick and dirty definition from an epidemiologist (hi!), you're looking for the moment when the number of cases of a given illness return to the "background" or baseline range. If an average year sees 2 cases of illness X within range Y, then the outbreak begins and ends when the rate of new cases in that range exceed and return to that range.
posted by late afternoon dreaming hotel at 2:21 PM on March 11, 2016 [2 favorites]


I'd add that WHO isn't like some central tabulating agency in charge of population-level health events. Definitions are flexible and reflect on local needs and population characteristics (like climate, socioeconomic status, prevalence of related illnesses, etc.). Your local health department might have standard operating definitions that differ from the definitions used a county over.
posted by late afternoon dreaming hotel at 2:23 PM on March 11, 2016 [7 favorites]


« Older Walk me through the process of dealing with my...   |   YANMD, YANMT: Where do I start as an anxious... Newer »
This thread is closed to new comments.