Does the personal health ever intersect with public health?
Absolutely, personal health issues and problems often influence the public health. Communicable diseases are good examples of the two intersecting. Take influenza for example, if someone has the flu not only is their health compromised, but the health of the people they have contact with is also potentially affected because of the contagious and virulent nature of the illness. Any communicable disease can easily and often does become a public health matter.
Many, many diseases fall into the category of public health threats. As humans, we pass disease and pathogenic organisms from person to person. Some illnesses are more contagious than others and are a cause for greater alarm. Public health officials like the professionals at the Centers for Disease Control monitor trends in disease transmission in an effort to protect the public health.
Personal health can intersect with public health in a variety of different ways. Say for example a person is sick with strep throat which is contagious. Perhaps they have to work that day. Knowing that they are sick they decide to go anyway and then throughout the day they end up spreading it to other people around them. Now, what started as one ill person, it now many. This happens with many different illnesses.
Another way that personal health can intersect with public health is by the overprescribing effects of antibiotics. Most doctors now days try very hard not to prescribe antibiotics when they are not needed. Years ago, many doctors did overprescribe antibiotics which made some bacteria very resistant to certain antibiotics.