Sewage screening, It's a Public Health Good Thing

Could the lowly sewage treatment plan be a key to protecting the public from Ebola and other infectious diseases? Absolutely. Are these facilities being used that way. Not in this country.

The recent Ebola cases in the United States (after, let's be quick to realize, the thousands of deaths in Africa) have reignited concerns about our ability to identify, treat, and isolate infectious diseases.

Despite the hysterical tone in many news stories, the number of confirmed cases in the US is well under a dozen. Only one patient, a man who was infected outside the country, is known to have died, and the others have either recovered or are getting better. We'll likely still see an individual cross contamination here and there from infected people to immediate family or a health care worker, but despite the fears of some well known authors who should know better, it's highly unlikely Ebola will “break out” to the general public.

There are numerous other diseases in this country which are equally scary, but after a bit of initial extra concern we've learned how to handle them and keep the counts under control. For example, tularemia has a reported incidence of 100 to 200 cases per year. Q Fever has similar numbers, and we typically have only a dozen or so cases of plague annually.

Even a disease like anthrax, which came to national attention during the "Amerithrax" scare shortly after 9/11 when (as we finally determined) a sociopath was mailing anthrax laden letters around the country, has a basic background level of under a dozen cases per year. And despite the best or worst efforts of Bruce Ivins, PhD, the letter sender, he only murdered five people and there wasn't a single case of secondary (ie, person-to-person infection).

One reason these diseases cause such fear is that, just like in the first years of what later became known as HIV/AIDS, the apparent mortality rate is extremely high. And that's a function of selected reporting.

When the US Centers for Disease Control and Prevention's “Morbidity and Mortality Weekly Report” ran its first story on this then unnamed syndrome back in July, 1981, the initial diagnosis of what turned out to be AIDS was frequently a near-term death sentence. The reasons were two-fold: First, we were just beginning to learn how to treat the related diseases and the tools we had were few and far between. But secondly, by the time there was an actual recognition of the case, the patient was (to be blunt) just about dead.

People with lesser or no symptoms (ie, carriers) weren't even counted in the numbers.

As we learned more about it, and both started detecting HIV/AIDs in “healthier” patients, and as treatments improved, the disease went from being an immediate death sentence to a long-term, chronic, and manageable state similar to diabetes or hypertension.

Of course, a key difference between HIV/AIDS and chronic conditions like diabetes is that that HIV/AIDS patients can infect other people.

Perhaps a better historical analogy is to polio. Prior to the widespread vaccination which just about eliminated it in the US and most of the world, exposure to the polio virus led to a wide variety in symptom intensity. Many people never got infected; many of those who were infected never got sick. The actual illness profile ranged from what appeared to be a cold and some weakness up to the horrendous paralyses we're all too familiar with.

And initially, at least, only the people suffering the worst were diagnosed with polio. The mild cases went undiagnosed.

Hence making decisions about the true risks from diseases requires solid information about the true background incidence, most especially including the rate among people who are either asymptomatic or have mild enough cases that they're just considered to have routine colds.

One key research tool for surveillance is sewage sampling. As people use toilet facilities, they excrete markers for polio and other diseases, as well as a wide variety of other interesting products such as legal and illicit drugs and their breakdown products.

Yet few, if any, US public health authorities require their sewer treatment facilities to routinely engage in such sampling. Most only look for some bare minimal EPA-mandated contaminants and markers such as E. coli and ammonia levels in the discharge.

Other countries, though, do these simple, noninvasive, and cheap tests for a variety of pathogens. And they have found fascinating results.

In the past year Israel discovered polio in sewage plants in its southern towns, yet did not have a single report of any patient diagnosed with the disease. This was apparently due to the huge refugee migration into the country fleeing warfare in the neighboring areas. There were similar finds in the sewage systems of Egypt, the West Bank, Gaza, and possibly Jordan. The public health authorities, both local and with international assistance, immediately began programs of polio re-vaccination to block any further spread.

The key point, again, is that there weren't any identified human cases, but that sewage screening picked up the disease before it led to serious human consequences.

These stories got me wondering about just how well the US handles this issue. I asked acquaintances in New York City's Department of Environmental Protection whether they screened for any of these markers. They told me they only looked for the basic E. coli and a handful of other contaminants as required under EPA mandates.

NYC's official response to a Freedom of Information Law request I filed was: “The Department's laboratories do not perform analyses as you described in your request as: analysis that might include level of radioactivity, the residues of pharmaceutical as well as illegal drugs, along with such disease markers as polio and its byproducts.”

A sewage manager interviewed at a small town in central Michigan (who wasn't authorized to speak on the record so must remain anonymous) described a similar process at his plant.

Given the low price and the high value of this data, one might ask just why this type of analysis isn't standard in this country.