The risk of contracting an infectious disease has increased significantly in the past several years, not only 'at home' in the U.S., but also with the 'import' of communicable diseases from other countries.
The Centers for Disease Control and Prevention, under the U.S. Department of Health and Human Services, monitors the incidence of communicable diseases. Current concerns include the Avian flu virus ('bird' flu), SARS (severe acute respiratory syndrome), and swine fever.
Even patients in hospitals and their nurses are more at risk of being exposed to communicable diseases. MRSA (methicillin resistant staphylococcus aureus) is one of several antibiotic / multi-drug resistant bacteria which generally attack people with weakened immune systems.