What killed Americans in 1776? The answer is dramatically different from today

The leading causes of death have changed dramatically since America's founding 250 years ago, highlighting how far medicine has come.

Diseases that once devastated communities have largely given way to chronic conditions, data shows, reflecting centuries of breakthroughs in public health, prevention and treatment.

"The amount of changes that have happened over the past 250 years are immeasurable when it comes to life expectancy and disease," Kenneth J. Perry, M.D., an emergency physician in Charleston, South Carolina, told Fox News Digital.

5 OF AMERICA'S GREATEST MEDICAL BREAKTHROUGHS REVEALED AS THE NATION MARKS 250 YEARS

"Our life expectancy as a country increased from roughly 30 years at the time of the country’s founding to close to 80 years today."

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Although there were no official national mortality records in 1776, historians agree that the following illnesses were responsible for the largest number of deaths.

These conditions had much higher fatality rates in 1776 because Americans had no antibiotics, few vaccines, no understanding of germ theory, no sterile surgical techniques and limited access to hospitals, experts note.

There was also a lack of safe drinking water, modern sewage systems and refrigeration — making it more likely for foodborne and waterborne illnesses to spread.

Patients also did not yet have access to blood transfusions, anesthesia and other lifesaving medical advances, according to the CDC, NLM and NIH.

The first official national mortality statistics were published by the U.S. Census Bureau in 1900.

The data points to the following leading causes of death in the 1900s.

Nearly one-third of all deaths were caused by pneumonia, tuberculosis and diarrheal diseases, and about 30% of all deaths occurred in children younger than age 5, records show.

The introduction of vaccines dramatically reduced certain diseases, including smallpox, polio, diphtheria, measles and whooping cough. 

In 1980, smallpox became the first human disease ever eradicated worldwide.

Improvements in clean water and sanitation also contributed to greater longevity, as cities built sewage systems, water treatment plants and indoor plumbing, according to the CDC. As a result, deaths from cholera, dysentery and typhoid fever fell dramatically.

Germ theory also emerged in the late 1800s, in which scientists discovered that germs caused disease. This led to vast transformations in surgery, childbirth, handwashing, sterilization and infection control, per NIH and the Science History Institute.

Routine screening has enabled earlier detection of breast, cervical and colorectal cancers, while improvements in surgery, radiation therapy, chemotherapy, targeted therapies and immunotherapy have helped many patients live longer.

A recent analysis by the National Cancer Institute found that prevention and screening accounted for about 80% of the cancer deaths averted over the past 45 years for five major cancer types.

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In the 1940s, the widespread use of penicillin allowed for the treatment of diseases that were once fatal, including pneumonia, strep infections, wound infections and sepsis.

Advances in childbirth — including prenatal care, Cesarean sections, blood transfusions, antibiotics and neonatal intensive care — also dramatically improved maternal and infant survival compared with colonial America.

The mid-20th century also ushered in improvements in heart disease treatments. The use of CPR, defibrillators, coronary care units, bypass surgery, stents, statins and blood pressure medications helped to reduce cardiovascular deaths, according to the American Heart Association.

In a vast contrast to 1776, chronic diseases now account for most American deaths, because people generally live long enough to develop them.

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Current U.S. health data indicates that the following conditions are now the leading causes of death.

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"The transformation of deaths in the last 250 years, largely from infectious diseases to currently chronic debilitating diseases, represents both success and new challenges Americans will have to face," Dr. Omer Awan, a physician and professor at the University of Maryland School of Medicine, told Fox News Digital.

The uptick in chronic diseases is driven not only by an increasingly aging population, but by people’s lifestyle behaviors, according to the doctor.

"The chronic disease epidemic has been fueled by lack of exercise, as well as diets rich in fats, salts and ultraprocessed foods," he told Fox News Digital. "This has also led to the rise of obesity, which contributes to many of the chronic medical conditions that are among the top killers for Americans in the modern era."

Public health advances can change the course of health for millions of Americans, Awan said.

"Just as vaccines and antibiotics prolonged life centuries ago, so can lifestyle changes, exercise and new therapies that target obesity — like GLP-1 drugs and medications that promote better metabolic health."