Soap helps spread it through all the laundry. In one study researchers gave sterile clothes to people and asked them to include the clothing in their regular laundry. E.coli infested almost half the sterile clothes after the full cleaning cycle. E. coli won't survive the dryer but salmonella bacteria and many viruses do survive. The very young, the very old, and immunocompromised people are most at risk.
Pathogens thrive when people live in crowded places and in unsanitary conditions.
International air travel makes it easy for germs to spread to new breeding grounds. Ironically, hospitals are fertile ground for passing infections. Intravenous drug use, unsafe sex, and improper food handling spreads disease. Perhaps most frightening of all is the fact that microbes are adapting to new climates and growing resistant to the very antibiotics designed to kill them. We change our lifestyles, they find an advantage.