Disease control

With the pioneering work in bacteriology of French chemist Louis Pasteur and German scientist Robert Koch, methods for isolating the bacteria responsible for a given disease and vaccines for remedy were developed at the turn of the 20th century. British physician Ronald Ross identified the mosquito as the carrier of malaria and laid the foundations for combating the disease.^[21] Joseph Lister revolutionized surgery by the introduction of antiseptic surgery to eliminate infection. French epidemiologist Paul-Louis Simond proved that plague was carried by fleas on the back of rats,^[22] and the Americans Walter Reed and James Carroll demonstrated that mosquitoes carry the virus responsible for yellow fever.^[23]

With the onset of the epidemiological transition and as the prevalence of infectious diseases decreased through the 20th century, public health began to put more focus on chronic diseases such as cancer and heart disease. Previous efforts in many developed countries had already led to dramatic reductions in the infant mortality rate using preventative methods. In Britain, the infant mortality rate fell from over 15% in 1870 to 7% by 1930.^[24]

In the United States, public health worker Dr. Sara Josephine Baker established many programs to help the poor in New York City keep their infants healthy, leading teams of nurses into the crowded neighborhoods of Hell's Kitchen and teaching mothers how to dress, feed, and bathe their babies.

Dramatic increases in average life span in the late 19th century and 20th century, is widely credited to public health achievements, such as vaccination programs and control of many infectious diseases including polio, diphtheria, yellow fever and smallpox; effective health and safety policies such as road traffic safety and occupational safety; improved family planning; tobacco control measures; and programs designed to decrease non-communicable diseases by acting on known risk factors such as a person's background, lifestyle and environment.

Another major public health improvement was the decline in the "urban penalty" brought about by improvements in sanitation. These improvements included chlorination of drinking water, filtration and sewage treatment which led to the decline in deaths caused by infectious waterborne diseases such as cholera and intestinal diseases.^[25]