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Fact check: Claim about growing number of diseases exaggerates, omits context

Valerie Pavilonis   | Paste BN

The claim: There were only 7 diseases in 1891, but now it's 10,000 and rising

A Facebook post claims the number of human diseases is soaring exponentially.

Misinformation about medicine and public health commonly spreads online, with recent assertions ranging from posts about pneumonia to hydroxychloroquine. 

“Did you know that in 1891 there were only 7 diseases?” says a Feb. 1 Facebook post. "Here we are 120 years later when we have 10,000+ officially registered diseases, and new ones are constantly on the rise.”

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The post amassed over 400 shares and 600 likes in less than 10 days.

But experts say this claim exaggerates the reality from the 1890s and ignores the fact that many diseases were identified since then due to improved ability to detect them – not because they were new diseases. The count of diseases today is in the ballpark but depends on the metric used.

Paste BN has reached out to the poster for comment.

Experts say there were more than 7 diseases in 1891

According to Mark Harrison, professor of the history of medicine at the University of Oxford, the post is “very misleading.” 

In the 1890s, Harrison said, there were only about seven diseases for which microscopic causes had been identified – for example, cholera and tuberculosis. But other diseases such as smallpox, influenza and typhus were well-known even though their root causes had not yet been discovered.

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Dr. Scott Harris Podolsky, professor of global health and social medicine at Harvard Medical School, said while disease categories are always changing, the medical establishment in 1891 definitely knew about more than seven diseases. 

William Osler, founding professor of Johns Hopkins University, published a book in 1892 titled “Principles and Practice of Medicine.” The book’s table of contents references many more than seven diseases.  

Naomi Rogers, professor of the history of medicine at Yale University, also described how books can help trace back knowledge of disease, saying that several — and probably hundreds — of medical dictionaries were in print at the time. 

Upon hearing about the post, Rogers said she immediately knew that seven diseases couldn't be right. 

“I began to, in my head, list diseases I knew that were around in the late 19th century,” Rogers said. “I got to maybe 45, 50.”

Since 1891, many previously unknown diseases have been discovered

The claim that there are many more diseases than in the past, Harris said, is also misleading. 

“We are elucidating the causes of diseases – e.g. genetic – which have probably existed for centuries,” Harris said in an email. “We also are discovering new infectious diseases because it is natural for new viruses, etc, to evolve. But many diseases have declined massively – e.g. polio, typhus, plague – and smallpox no longer exists as a wild disease.”

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Rogers explained how the germ theory of disease – discovered and popularized between 1850 and 1920 – helped scientists categorize and understand different diseases. For example, Rogers said, you could no longer have a disease simply called “fever” since those fevers were now attached to a myriad of underlying causes. 

Diseases also evolve, Rogers added, and she gave the salient example of COVID-19. Coronaviruses were well-known before the pandemic, and COVID-19 is “just a new version.”

Disagreement on current disease tally

The number of diseases present today depends on the metric used.

The World Health Organization estimates there are more than 10,000 monogenic diseases, meaning they involve only one gene. The National Institutes of Health has more generally referred to there being thousands of diseases, The Washington Post reported in 2016 in a fact-check on a similar claim.

The Post noted several sources use a figure around 10,000, but there are outliers as well. The German government at the time listed 30,000 diseases, while countries like Japan have much more restrictive criteria.

Our rating: Partly false

Based on our research, we rate PARTLY FALSE the claim that there were only seven diseases in 1891, but now it's 10,000 and rising. Experts say doctors at the time knew about many more than seven diseases. The official number of confirmed diseases today differs depending on the criteria used, though many use the 10,000 figure. But the rise in disease counts since 1891 can be attributed to scientific advances that made discovering diseases possible. 

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