Final answer:
The decline of infectious diseases in developed countries can be attributed to improved sanitation, public health initiatives, behavioral changes, and medical advances such as vaccines and antibiotics.
Step-by-step explanation:
The key factors contributing to the decline of infectious diseases in developed countries are multifaceted and have significantly improved public health outcomes. The development and use of antibiotics and vaccines have been instrumental in controlling diseases that were once widespread and often deadly. Public health initiatives, including improved sanitation with clean water and sewage systems, have prevented the transmission of many infectious agents.
Changes in public behavior also contributed greatly, such as increased hand washing, food safety practices, and reductions in smoking. Behavioral changes aimed at reducing sexually transmitted diseases have likewise played a part. Finally, medical advances have had a tremendous impact on reducing infectious diseases, highlighted by the development of immunizations and antibiotic drugs, which, along with treatments for conditions like high blood pressure, have extended life expectancy significantly.