In a recent Scientific American article (Februa ry 2010), The Art of Bacterial Warfare, the authors state that 33% of humans are carrying the Mycobacterium tuberculosis bacteria-many without actually getting sick. In addition, 50% of the human population is carrying the bacteria Helicobacter pylori (which causes stomach ulcers), and 50% is carrying Staphylococcus aureus (which causes skin infections). Knowing that carriers are individuals who often do not show any visible signs of disease, what challenges can you think of for health officials trying to control these types of communicable diseases?