Thread by @BFCoutreach

🧵 Hey friends. This is your friendly public health nurse/medical geographer. We need to talk about the word endemic. A thread.

In epidemiology, an endemic disease is one that’s reached a steady state of transmission. This means that cases don’t increase exponentially, but the infection doesn’t die out, either. If you made a graph showing the total number of cases over time, you’d get a diagonal line.

You might have lots of new cases every day (a steep rise) or just a few cases each day (a gentle rise). The important thing is that the slope remains consistent - the line isn't getting steeper and steeper like in an epidemic, where we have exponential growth.

That’s what endemic means. In a population where everyone is susceptible, an infected person infects an average of one other person (in other words, the R number equals 1, since everyone knows what R numbers are now).

This definition of endemic is based on how an infection spreads through a population, not on disease severity, social disruption, distribution of cases, or incidence. An endemic infection can be common or uncommon, severe or mild, more disruptive to society or less.

For example, tuberculosis is often considered endemic to most of the world. According to the WHO, 2 billion people are infected with TB and 1.5 million people die from the disease every year. who.int/news-room/fact…

Malaria is often considered endemic. In 2021, the WHO estimates there were 241 million cases and 647,000 deaths. who.int/news-room/fact…

Notably, both of these infections are rare in the United States and most Americans have the privilege to ignore them. They’re endemic diseases that are deadly and disruptive, but not to us, so we might not be thinking about how endemic doesn’t inherently mean mild.

Endemic can also mean a disease is only found in one specific location (this definition is used in other ways, too - e.g. California has many endemic plant species). Ebola, Guinea worm, and river blindness fit this definition of endemic. They all suck, mostly for poor people.

The new meaning of endemic that’s arisen during the COVID pandemic isn’t based in disease dynamics. Public health professionals, medical providers, journalists, and government officials are increasingly using the word endemic to mean some version of “getting back to normal”.

When people ask, “When will we get to endemic?”, what they really mean is, “When can we reopen?”, “When can the masks come off?”, “When will COVID be less disruptive?”, and maybe, “What amount of disease and death is acceptable to us?”

If we get to a point where COVID continues to devastate elders, immunocompromised people, and chronically ill and disabled people, will that mean it’s “endemic”?

If we get to a point where COVID is like HIV, where your privilege determines whether you get to ignore it, will that mean the pandemic is over?

What if we find a way to keep our healthcare system teetering just on the edge of collapse without quite falling over so that everyone who isn’t a healthcare worker can pretend the system is working fine, will that mean we entered the "endemic phase"?

What we need to be asking is, what is the “normal” that we’re trying to get back to? Whose deaths are acceptable to us? What level of disease are we willing to accept as normal or inevitable?

If we get to a point where we don't have an exponential increase in cases, that's great, but that doesn't mean exponential growth can't return - R-numbers are not fixed properties of infections. It doesn't mean people won't stop dying or that COVID is mild.

If individual cities like San Francisco think they're "getting to endemic", they should also remember that cities are connected to the rest of the world - this crisis won't be over until it's over everywhere.

And endemic does not mean we get to go back to normal. Normal is how we got here, and normal will continue to bring us new crises until we collectively decide to stop accepting it.