For centuries now, mankind has had indoor plumbing.

It is one of the hallmarks of civilization, for it contributes to stable public health and suppresses the spread of infectious disease.

But in areas governed by a certain ideology, the public health situation has become so bad — virtually medieval — that diseases long thought to be eradicated are making a potential comeback to plague-city populations.

Welcome to San Francisco, California.

Under Democratic Party rule for more than several decades, the City by the Bay increasingly has become a haven for the very poor and the very rich — the exact opposite of the stated aspirations of Democratic Party platforms.

Young tech millionaires share the city spaces with the homeless and indigent in a scene more reminiscent of pre-revolutionary late 18th century Paris or Dickensian London than a modern American city.

Related: San Francisco Finds Itself in More Trouble

And the health crisis?

Fox News medical correspondent Dr. Marc Siegel spoke to that earlier this week on “Tucker Carlson Tonight.”

“Isn’t it ironic that a city of germaphobes, of exercise-conscious, environmentally conscious [people] … [is] now a city that’s awash in human waste, which is spreading hepatitis A outbreaks every year?” he said to Carlson, in part. “Big outbreaks of hepatitis A, rats in the streets feeding off the garbage in sewage, typhus, typhoid fever, rotten bacterial infections and even the plague may be coming.”

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Siegel added, “And here’s the other thing that’s even worse. It’s not just the homeless population, right? People trek through those neighborhoods. They get [human waste] on their shoes and then they bring it to other neighborhoods — and then the diseases spread to other neighborhoods.”

Rampant filth and disease as a public health crisis is becoming typical to one-party politics.

Today, in Venezuela, in Portland, in Los Angeles, in Seattle, and in other socialist bastions, homeless people and more are suffering from the same lack of basic health standards.

And because of one-party state socialist economic policies practiced in the city and at the state level, San Francisco is no different.

This is not San Francisco’s first time at bat with such problems, of course.

During the heyday of the “flower power” movement in Haight-Ashbury in the mid-to-late 1960s and early 1970s, basic health levels were so low in the counterculture community that rickets and scurvy — medical conditions believed gone from modern life — made a reappearance, only to dissipate once the movement itself moved on.

With socialism comes not just economic deprivation, in many cases — but often the loss of the most basic of services and health routines needed to maintain the modern civilized state of a city.

It is a lesson not lost on some.

But apparently, it’s been lost to the Democrats who run San Francisco and California.