A general term for diseases caused by pathogenic microorganisms that can spread between individuals. Often used in medical or public health contexts.
Hand washing is important for preventing infectious diseases.
An infectious disease is spreading in this region.
伝染病 emphasizes contagious diseases that spread directly from person to person, whereas 感染病 includes all infections regardless of transmission route.
Compound of 感染 (kansen, 'infection') and 病 (byō, 'disease'). The exact historical derivation is uncertain, but the term follows standard Sino-Japanese word formation patterns.