The Chicago River health study: time to clean up the River, not grade it on a curve

The Metropolitan Water Reclamation District’s study of the human health impacts of Chicago River recreation, more than three years in the making, is finally out.  According to the District, the verdict is in:  come on in, the water’s fine.  Or at least, no less fine than Lake Michigan.  Seizing on portions of the report that found the rate of some kinds of illness to be high in both the River and in cleaner waters, the District has generated a glossy pamphlet telling us that we no longer need to worry about disinfecting sewage discharge to the River since people are getting sick everywhere.

Feel better now?  I, for one, will be keeping my canoe paddles in storage for just a bit longer.  So, it seems, will the editors of the Chicago Tribune, who came out forcefully in favor of disinfection within less than a week after the District released its study.  Much as it would be nice to believe that everything is miraculously hunky dory on the River, and that Chicago can stop worrying about being virtually the only major city in the nation that still doesn’t disinfect its sewage, the District’s study unfortunately doesn’t take us there. 

The study, an epidemiological investigation known by the perky acronym CHEERS (“Chicago Health, Environmental Exposure, and Recreation Study”) was performed by researchers at the University of Illinois at Chicago who were commissioned and paid by the District.  And I will start out by saying, not that there’s anything wrong with that.  Science is good, and the UIC researchers are all conscientious and meticulous scientists, notwithstanding who was paying them.  And the study is really very well done:  its methods are thoughtful and its analysis reasonably thorough.  Essentially, what the researchers did was to recruit more than 11,000 people who engage in non-immersion water recreation (boating and fishing, not swimming) on the River and on cleaner “general use” waters, as well as people who recreate away from the water, and look at the relative rates at which they got sick – with gastrointestinal problems, skin rash, eye infections, that sort of thing.  It involved a lot of questions about what people did, how wet they got, and how they felt afterwards.  And testing the water.  And stool samples kept in people’s refrigerators, but we won’t get into that.  

So what did they conclude?  Well, first off, not that everything’s ok.  The study found a definite link between water recreation on the River and one type of illness that people worry about in dirty water:  what the study referred to as “eye symptoms,” meaning nastiness like redness, crusting, itching, and discharge.   People who recreate on the River had a 55 percent greater chance of developing eye symptoms than people who don’t engage in water recreation, and a 37 percent greater chance than people who recreate in cleaner waters. 

What the District focused on, though, is the portion of the study that found almost equally elevated levels of gastrointestinal illness (GI) among River and cleaner water recreators.  Specifically, the CHEERS study found that people recreating on the River were 40 percent more likely to contract GI than non-water recreators, while people recreating in clean water were 44 percent more likely.  Put another way, they found 12.5 cases of GI illness per 1,000 recreators directly attributable to River recreation, and 13.4 cases per 1,000 attributable to cleaner water recreation.

Or put yet another way, that’s a lot of cases.  The benchmark used by the US Environmental Protection Agency to determine when they should close the beaches to swimming is 8 cases per 1,000.  That is, if they determine the water is dirty enough to make more people than that sick, then everybody out of the water. 

So I suppose you could conclude from that that we don’t need to do anything, because everyone’s getting sick at the same rate.  Particularly, I guess, if you’re a large and rather set in your ways public institution that seems beset by a visceral need to object to modernization initiatives.  I, on the other hand, would be more inclined to conclude from it that we may have an even larger problem than we thought.   If the water is really making people sick in both places, maybe we should try fixing the problem in both places rather than just grading them on a curve.  Particularly since the southern end of Lake Michigan is home to some of the dirtiest beaches in the nation.

Yet the truth of the matter is, the only thing we can responsibly conclude from the CHEERS study is that good science usually raises more questions than it answers.   And any epidemiologist worth their salt will tell you that this is particularly true for epidemiology, because unlike most scientific research it is not conducted in a lab where study conditions can be tightly controlled.  Epidemiologists do their research out in the messy real world, where they seek to determine whether one particular thing is making people sick when a thousand other things may be making them sick as well.  In other words, epidemiology is more or less the science of looking for needles in haystacks.  And the failure to find a needle on the first go-round really isn’t conclusive proof that it’s not there.   It may well just raise more questions about where to look for it.

And the CHEERS study, as good as it is, is no exception.  Not only was it subject to the usual needle-in-a-haystack limitations of epidemiology, but by design was simply not equipped to tell us everything we need to know about the safety of River recreation.  For one thing, it was only a survey of the general population.  That’s fine for a first look.  But it doesn’t tell us anything about the risk specifically to people who are inherently more likely to get sick than average:  kids, pregnant women, and others whose immune systems are not as strong; and people whose activities are more likely to result in getting really wet, like kayakers.  For another thing, there’s a lot that may have gone wrong with the process of asking 11,000 people questions and hoping for accurate and helpful answers.  For example, do all 11,000 people mean the same degree of wetness when they say they got “splashed”?   And are we really comparing apples to apples?  The level of germs within both the River and the cleaner waters varies quite a lot.  What if people studied were predominantly recreating in the cleaner parts of the River, but the dirtier parts of the Lake?

And so on.  NRDC’s epidemiology expert in the Pollution Control Board Proceedings, Dr. Marc Gorelick of the Medical College of Wisconsin, has described numerous ways in which the CHEERS study, while fundamentally sound, has the kind of gaps in information that pretty much any real-world study like this is going to have.   

But perhaps most importantly, Dr. Gorelick – who has himself published more than 50 epidemiology research papers – wants the Board to understand that the inherent limits of epidemiology require that it be understood and used only in the context of the science we already know.  And if there’s one thing that medical science definitely already knows, it’s that germs can make you sick. 

So carry on with the study of risks on the Chicago River.    We hope that the skilled and dedicated epidemiologists at UIC and elsewhere will continue to answer the questions raised by the CHEERS study.  But in the meantime, let’s get the germs out of the water .