“You can take the microbiologist out of the lab, but you can’t take the lab out of the microbiologist”

I was fortunate enough to attend the Olympics in Paris last month, the first time I have ever been to the Olympics. It was a fantastic experience, and we managed to see several events, including football, tennis, athletics, cycling, Rugby 7s and triathlon. Moreover, Paris is my favourite city, so I take every opportunity to visit!

I was hoping to forget all about all things microbiological for a month, and to a large extent this happened, until I was watching the triathletes swimming in the Seine!

You are probably aware of the story, but it was a big thing, and something of a propaganda stunt, allowing the Olympic athletes to swim in the River Seine, and the French Government invested heavily in cleaning up the Seine in order to facilitate this. 

In the end it was touch and go. Heavy rain before the Olympics put the E.coli counts up in the river, and at least one of the training sessions and the men’s individual event had to be postponed due to levels exceeding the acceptable limits.

A few athletes got sick after swimming in the Seine but of course it was virtually impossible to prove that the river swimming caused the illnesses.

Which got me thinking. “What are the acceptable faecal contamination limits for swimming in rivers, and is the risk any different for elite athletes in the Olympics?

There are safety standards set by World Triathlon, which indicate that colony-forming units (CFU) of E. coli per 100 milliliters of water should not exceed 1,000 and enterococci levels should be below 400 CFU/100ml. As one can see from this report, levels were acceptable on the day of the race, but not on several other days.

Of course, the cut-offs for E. coli and enterococci are completely arbitrary… The higher the counts, the higher the level of faecal contamination, and thus the higher the risk. E. coli and enterococci are of course only indicators, as most E. coli and enterococci do not cause gastrointestinal illness. There are a whole range of infections that one can acquire by swimming in faecally contaminated river water, including bacteria, viruses, & spirochaetes. Gastroenteritis is likely the highest risk but ear infections and skin infections can also occur.

There are several other factors that may affect the overall risk. The risk will depend on the range of gastrointestinal pathogens present in the water. I.e. swimming in a river in India might carry a different risk to swimming in a river in Paris even if the E. coli levels are equivalent. The amount of water ingested will also be a factor. I imagine an elite athlete going hell for leather in the Olympic triathlon will be intaking a lot more water whilst swimming than if President Macron goes for a leisurely dip in the Seine, if he ever does. The exposure time will also be a factor. The athletes competing in the 10km distance swimming event will have a lot more cumulative exposure than the triathletes swimming 1500m. Finally, the “host” needs to be taken into account. The cohort swimming in the Olympics will be overwhelmingly young, fit and immunocompetent thus potentially at less risk than the general population.

So clearly it is not as simple as just saying >1000 E. coli per 100ml of water is unsafe and less than that is safe. It is far more nuanced than that.

For elite athletes, whose livelihoods depend on competing in such events, they really have little choice in the matter. For myself however, who is definitely not an elite athlete, I like looking at the Seine, and it certainly appears cleaner than in years gone by, but I will pass on the swimming just for now.

Michael