The Romans may have been one of the first civilizations to have indoor plumbing, but it seems that claims to their effectiveness have been greatly exaggerated. A recent paper published in Parasitology indicates that, rather than helping prevent disease, members of the Roman Empire instead saw a gradual increase in communicable parasites.
The sanitation system in Rome, including plumbing and aqueducts to carry away dirty water, feces, and urine, was built to prevent common parasites. While it came before the germ theory of disease, the ancient Romans of approximately 2,000 years ago still seemed to have some indication that pathogens were spread through poor hygiene.
And yet a recent stool analysis conducted by researchers at Cambridge found that despite these efforts tapeworm, ringworm, whipworm, and dysentery-causing bacteria persisted in the bodies of ancient Romans.
Indoor plumbing clearly gives us a sanitation advantage today, so where did they go wrong? It may have been in inconsistent application of sanitation measures. For instance, while public baths were intended to keep Romans squeaky clean, the water was not frequently changed, effectively creating a soup of fleas and worms for the next person to bathe in. The researchers also addressed ectoparasites like fleas and lice, stating that delousing combs were common. They, too, could have been transmitted via shared bathing.
In addition, while the Romans may have taken a sanitary approach to doing their business, their food could have used some safety measures. For example, the condiment garum, a Roman fish sauce that was commonly added to meals, was prepared by leaving it to ferment in the sun. Parasitic worm eggs didn't have a chance to breakdown and, instead, spread through more consumption of garum.
Food may have played a role in a different way, as well. While human excrement was carried away from cities, it still found its way to farms as a fertilizer, providing another opportunity for common maladies to find their way back to the city.
All these factors may have led to a sort of cancelling-out effect of Roman sanitation systems. Rather than helping drive down disease, the other measures brought it right back, and made the Romans no more or less healthy than other European groups without indoor plumbing or regular bathing, like the Vikings.