Petri dishes are small plastic containers filled with nutrients facilitating the growth of bacteria for culture and identification. In keeping with America’s theme of super-sizing everything, we now have petri dishes large enough to be measured in square miles.

I refer to American cities, specifically those on the West Coast, Los Angeles, San Francisco, and Seattle. Remember how Democrats and the media howled with outrage when President Trump referred to El Salvador, Haiti, and some African countries as “s—holes”?

CNN accused Trump, as they do most days, of being a racist for correctly pointing out that refugees from these countries bring a host of nasty diseases to America. Never mind that residents from the above-mentioned countries are of different races, negating the racist argument.

When you bring there here, here becomes there. Now it’s not just Central American countries that are fetid, but previously beautiful and prosperous American cities.

The number of homeless in Los Angeles County jumped 12 percent over the past year with now about 60,000, assuming they can all be adequately counted. City sidewalks are littered with tents and piles of trash, something one doesn’t expect to see in the City of Angels, but rather in some third world city far away from America.

Up the coast in San Francisco is where Tony Bennett once left his heart. But residents now leave their poop, not in the toilet but on the streets and sidewalks. 132,562 cases of human waste were reported over the past ten years, with far more going unreported since it has become the norm in San Francisco.

It’s gotten so bad that a poop map is available online, guiding residents and tourists where to walk and step to avoid any of the 28,000 poop sightings in 2018.

Further up the Pacific coast in Seattle, there are over 11,000 people sleeping in tents and cars. The usual Democratic solution of throwing money at the problem isn’t working. Despite spending more than $1 billion per year on homelessness, or $100,000 per person, the problem has only worsened, just as most problems do after Democratic solutions.

These cities have much in common. They are all sanctuary cities, welcoming illegal immigrants from who knows where. They are all run by Democrats, at the city, state, and federal levels.

These politicians are quite happy to virtue signal on global warming and transgenders in women’s sports but do nothing for their cities. After all, they are safely ensconced in their mansions, behind fences or walls, occasionally driving past tent cities, but personally living worlds away from what their constituents face every day.

These conditions create the perfect storm for a city-wide petri dish. As a result, medieval diseases have moved from the history books to the streets of L.A. Typhoid fever, typhus, hepatitis A, and tuberculosis are on the rise in Los Angeles.

As many have described, these disease outbreaks are linked to the homeless problem, spread by fleas and feces, both prevalent in homeless encampments. Los Angeles police stations are infested with rats and other vermin.

One L.A. police officer is being treated for typhoid fever, and another five are showing typhus-like symptoms. Not surprisingly, the journalistic sleuths at ABC News say, “It’s unclear what caused the officers’ illnesses.” Then in the next sentence acknowledge, “Los Angeles has been dealing with a growing rat infestation and typhus outbreaks since at least October 2018.”

This is typical for the media, always puzzled by motive, just as when a swarthy young male shouts “allahu akbar” before opening fire in a gay nightclub.

What might be ahead for American petri dish cities? This week, a group of 116 African refugees were apprehended after illegally entering the United States. Many came from Congo, where there is currently an Ebola outbreak. What about those not apprehended by overworked border control agents? How many might make their way to Los Angeles or Seattle, adding their germs to the already fetid petri dishes?

The common denominator is Democratic policy. Artificially high minimum wages increase unemployment, particularly among the more vulnerable. Decriminalizing bad behavior such as drug use, alcoholism, and petty crimes leads to more of such behavior. Open borders and sanctuary cities are magnets for unvetted, potentially sick, illegal immigrants bringing exotic diseases from their home countries to American cities.

No solutions are forthcoming from Democrats. They’re proposing green new deals, full-term abortions, and impeachment or prison for President Trump. These are not solutions, only noise. Meanwhile, once-beautiful American cities are rapidly becoming unlivable and, in many cases, dangerous, worthy of quarantine or large-scale decontamination.

Republicans are missing a great opportunity to educate voters and to clarify the policy differences that determine whether American cities “shine on the hill” or become mass petri dishes.

Brian C. Joondeph (@RetinalDoctor), MD, MPS, is a Denver-based physician.

The views and opinions expressed in this commentary are those of the author and do not reflect the official position of The Daily Caller.