In infectious disease, we tend to talk about the triad of factors which lead to disease.  These factors are host, agent, and environment.  In human disease, the host is a human, of course, but each human comes with a set of genes, co-existing diseases, nutritional status, and so on.  An agent is something which causes disease-a bacteria, a virus, or a toxin.  And environment is, well, environment.  The milieu in which one lives.  The world around you-clean or dirty, safe or dangerous, pleasant or ugly.

Medical students are taught this paradigm early on, usually during microbiology in their first year.  And after that, most of us go on to forget environment entirely, concentrating on host and agent.  In some ways, this is predictable-we see the hosts as patients, and the agents as the enemy.  And it has resulted in a lot of success for us as physicians; while I continue to decline the “best health care system in the world” appellation, we physicians are, individually, often excellent at what we do, and occasionally, we rise as a team to something near excellence, in individual cases or groups of cases.

We’re at the point, though, where working at the host/agent interface, while effective, is more and more costly.  If we want maximum bang for our buck, or even to make the bucks we’re spending elsewhere more effective, we must act on the environment.  In part, we should do this because, like any three legged construct, if we make two legs strong, the third leg will inevitably break and we fall.  In part, of course, we should do it because it’s right.  But mostly, in my opinion, we ought to do it because if we do we can get better health for free.

(Well, relatively free.  Cheap, anyway).

What’s the environment, in this situation?  It’s everything that isn’t host, essentially.  How easy is it for you to get food?  How stressful is it to walk around in your neighborhood?  What toxic substances are in your soil, your water, your air?  All of this matters, because it all informs what sort of host you present to the agents.  If you are constantly exposed to a low level of a toxin, your reaction will be different when exposed to a high level of that same toxin, or a related one.  (Might be better, might be worse; it depends.  Point is, it’ll be different, and the differences are part of why you either stay well or get sicker than someone from a different environment).  If you are chronically stressed, your reaction to a minor additional stress will be different than someone who generally has it pretty good (this is one of the theories of why African-Americans have higher rates of things like high blood pressure and cardiovascular (heart disease and stroke) issues.  Racism, goes the theory, makes your general stress level higher, and this translates into higher disease rates.  It has the advantage of being plausible; it has the disadvantage of being hard to craft a policy solution around.

And here we come to the point of this little diatribe.  Environment matters in health.  It makes you who and what you are, and in turn it dictates, in some ways, how you will respond as a biological organism to a health threat.  In the US, though, we seem entirely content to ignore the role environment plays in disease, especially if it means improving the environment of someone other than ourselves.  We (a significant fraction of “we”, in any event) dislike government regulation of the environment.  We don’t like the idea of transferring our wealth to improve the health of others.  But we balk much less (so far) at the idea of transferring our wealth to cure these folks once their environment has made them sick (which is essentially what laws like EMTALA, the Emergency Medical Treatment and Active Labor Act, require; if you get sick, you must be treated-as long as you can drag yourself to an emergency department, or in some jurisdictions, can get an ambulance to pick you up).

Are we, anytime soon, going to realize that we are being penny-wise and pound foolish?  Money spent to improve the health of a whole population really does “lift all boats”; healthier people are consumers for longer, can provide you services better, or be better employees, or better employers, or any number of things which will make your world better because there are healthier people in it.  And “environment” often has very porous walls; a problem in someone else’s environment, be it a toxin or a level of social unrest, has a way of leaking into your environment, whereon it is the very devil to get back out without getting it out of every other place where it can be found.  This was a lot of the point behind the advances in public health made in the 19th century – laws to improve everyone’s health by improving the environment (“No Spitting” laws made an enormous dent in decreasing TB transmission well before we could treat TB), really did improve everyone’s health, rich and poor alike (if your servants don’t have TB, you are less likely to get it, for instance).

In high school, I chanced to read a poem by John Donne, about how no man is an island.  The last line has always struck me, especially if read the right way, as by an advisor to a king: “Send not to know for whom the bell tolls.  It tolls for thee”  (John Donne, Devotions Upon Emergent Occasions (1624), Meditation XVII).