(CNN) -- Cholera is an intestinal infection that's rare in the United States currently.
But in the developing world it's a serious problem, with 3 to 5 million cases every year worldwide, according to the World Health Organization.
The disease brings on diarrhea, which can kill a person if he or she is not properly hydrated. A tremendous advance in hydration was invented by David Nalin, along with his colleague Richard Cash.
Nalin was working in Bangladesh during a cholera epidemic in 1968, when intravenous solutions were the only treatment. He knew that an oral method of rehydration would be much more accessible and cost-effective for the people who needed it most.
This idea had been around before. Other doctors had tried oral methods but failed because they had the wrong proportions, and because they were focused on trying to give every person the same "magic bullet" dosage of therapy.
Nalin recognized that the volume of oral rehydration therapy required isn't the same for every patient. Individual losses need to be replaced with equal volumes of the absorbable solution.
What exactly did he deliver to patients? Essentially, a mixture of salt, water and sugar in the right proportions. This simple idea has saved millions of lives -- not just from cholera, but from any diarrhea.
The Lancet, a prestigious British medical journal, called this "potentially the most important medical advance of this century."
"The devastating conditions suffered by the Bangladeshi refugees as they fled the war with Pakistan offered ORT (oral rehydration therapy) its definitive test," according to an August 2003 paper published in the journal Clinical Infectious Diseases.
"When the medical team ran out of intravenous fluids at the camp, oral glucose-salt packets were used to treat (more than) 3,000 patients, resulting in a reduction in the mortality rate from 30% to only 3.6%," the journal said.
CNN's Edythe McNamee contributed to this report.