Romans didn't view bathroom functions to be, as our name for them applies, something to be done in a place dedicated for that purpose. If you were a Roman citizen out on the town with your buddies, you wouldn't peel off one at a time to use a washroom. You'd all sit down together on a public urinal and keep the conversation going as you dropped your deuces. Many Roman houses did have toilets, but they were usually in the kitchen, of all places! This flies in the face of modern notions about sanitary food preparation, but also in the face of privacy. If you were Roman, taking a dump was, more often than not, done in full view of others.
One thing that really is mind-bending about the ancient Romans is their total lack of privacy. You went to toilet in public, with friends. You went to the toilet in your home as your slaves prepared food around you. You had sex with a slave standing over you in case you got thirsty and needed to send for water. Being alone for any reason was a totally foreign concept. Slaves talk. Anything you did was public knowledge in fairly short order. For this reason, Romans also really didn't have the concept of the self-defined man. For example, donating anonymously to feel good about yourself was simply not done. Who you were was what people thought of you.
The paper doesn't mention population density, but I'd think that would an important part of the story. Keeping infection rates at the same level in urbanized, densely populated areas as is present in places where people live in more widespread, small agricultural communities seems like a pretty important deal.
It's hard to imagine the larger Roman cities, and Rome itself, could exist without some manner of legal and technological organization to manage sanitation.
To put some numbers on this, about 600 million Indians rely on open defecation. Some researchers think that this is a key to the "Asian enigma"--the problem of why Indian children are shorter on average than African children even though African children are on average poorer (which normally correlates well with height).
Researchers have found that open defecation leads to stunted growth, and also higher child mortality rates. The later could explain another puzzle of India--why Hindu children have higher mortality rates than Muslim children, even though Hindus are on average richer and more educated.
It turns out that Indian Muslims are about 20 percent more likely to use toilets than Indian Hindus, regardless of income level.
India was the birthplace of plumbing, though the Romans perfected it.
Standardized earthen plumbing pipes with broad flanges making use of asphalt for preventing leakages appeared in the urban settlements of the Indus Valley Civilization by 2700 B.C.[5]
I am not in the position to judge the situation in India but invention does not necessarily imply widespread adoption. Or adoption may change over time, for example by not keep up with population growth.
Which is really ironic because flush toilets were normal in Indus valley civilization. That would be 2500 BC or another 500 years earlier. Centuries ahead of its time
One thing that really is mind-bending about the ancient Romans is their total lack of privacy. You went to toilet in public, with friends. You went to the toilet in your home as your slaves prepared food around you. You had sex with a slave standing over you in case you got thirsty and needed to send for water. Being alone for any reason was a totally foreign concept. Slaves talk. Anything you did was public knowledge in fairly short order. For this reason, Romans also really didn't have the concept of the self-defined man. For example, donating anonymously to feel good about yourself was simply not done. Who you were was what people thought of you.