(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 los