Thread by @jasoncrawford

Infectious disease is a multi-front war: Sanitation removes germs from the environment. Vaccines provide immunity. Antibiotics fight active infections.

But historically, what mattered most? I was surprised when I started digging into the data:

rootsofprogress.org/draining-the-s…

Vaccines and antibiotics get the spotlight in most histories. But they weren't in widespread use before about the late 1930s.

And it turns out that infectious disease mortality rates were dropping since long before this. (First chart: US, second: England & Wales)

In fact, probably *much* longer.

Here's data showing overall mortality rates dropping in various European countries since the mid-1700s, and I've read that there is evidence of a decline starting in the 1670s.

So what was going on?

In short, there were many improvements in sanitation and hygiene, over the course of at least two centuries.

In the 1700s, a number of European physicians “embarked on a vast campaign to assemble qualitative and quantitative data about epidemics” and correlate them with environmental factors.

They didn't discover a scientific theory of disease…

… but they were able to come up with a list of practical interventions. Draining swamps, ventilating rooms, burning sulfur sticks (an early insecticide), burying bodies *outside* the city, and generally removing waste from the human environment.

In particular, these all had the effect of reducing insect populations. Insects were the vectors for some of the worst disease of that era, such as malaria and typhus, and they helped spread others such as dysentery. Mosquitoes, lice, flies and cockroaches were all culprits.

As the countryside was getting cleaned up, however, people were migrating in droves to cities, which became crowded and polluted. Human waste collected in cesspools or flowed through cobblestone streets. Malaria was on the wane, but cholera was on the rise.

The cities were thus more disease-ridden than the country in this era, and mortality rates were higher among city-dwellers. Overall mortality rates actually plateaued in the mid-1800s as sanitation improvements were cancelled out by the migration to cities.

Soon, reformers across Europe were calling for sanitation improvements, starting with water and sewage. From London to Paris to Munich, and in the US as well, cities found cleaner water sources, often further upstream, and implemented basic filtration using sand.

They built or extended sewer systems, getting rid of local cesspools were waste would just sit until it was cleaned out (too rarely) by sanitation workers. And most importantly, they dumped the sewage far downstream, to keep it separate from drinking water.

All this began to improve mortality especially from waterborne diseases such as cholera and typhoid fever. But these early efforts were crude, guided only by smell, taste and color. They were for aesthetics and much as for health.

Until the germ theory was finally established.

After Pasteur showed how bacteria could cause disease, and Koch identified the tuberculosis bacillus, the world had a new scientific theory to guid them, and new methods, such as microscopy.

Vaccines and antibiotics were still decades away. But public health was revolutionized.

Around the turn of the 20th century, water filtration was upgraded to be more effective against bacteria, and chlorine was added to kill germs that weren't filtered out.

Here's how that affected typhoid fever in Pittsburgh:

The paper that chart comes from estimates that filtration and chlorination explain “nearly half of the overall reduction in mortality between 1900 and 1936”, “three-quarters of the decline in infant mortality” and “nearly two-thirds of the decline in child mortality.” (!)

Food handling was improved, too. In the 1800s, milk was transported warm in open containers, making it a literal breeding ground for bacteria. Pasteurization (introduced around 1900) and sealed tins and bottles improved health, contributing to this decline in infant mortality:

Finally, public health officials educated the populace about general hygiene. They printed pamphlets, produced films (such as “The Fly Pest”), and answered letters from parents on child care.

So what about antibiotics? By the time they were invented, mortality rates from infection had already been reduced by a large factor. In the US from 1900–37 they were dropping 2.8%/year.

But during the golden age of antibiotics in 1937–52, they fell *8.2%/year*:

And vaccines? They eliminated smallpox and polio (both viral infections that antibiotics can't touch). But for other diseases, they mostly came along late in the game to mop up what was left after the impact of sanitation improvements.

They're fantastically effective, though, having reduced morbidity for several important diseases by over 99% (cdc.gov/mmwr/preview/m…):

Bottom line: sanitation—pest control, improved water and sewage, pasteurization and other food safety, and public hygiene education—probably did more than anything else to reduce mortality rates, if only because these techniques were available a long time before anything else.

But just because medical treatments didn't rack up the most points on this scoreboard, doesn't mean we can't credit medical technology for these improvements, if we construe “medicine” broadly enough to include public health efforts.

Or since this is Twitter, in meme form:

See the full post for more detail and full references: rootsofprogress.org/draining-the-s…

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