By Davis W. Cheng, Ph. D.

The terms “Contagious Disease,” “Infectious Disease,” and “Communicable Disease” are related concepts and often used interchangeably, but there are distinctions in their meanings and subtle differences in emphasis. 

“Contagious Disease” specifically highlights diseases easily transmitted from person to person. Contagious diseases have a high potential for spreading through direct or close contact with an infected individual or contact with contaminated surfaces or objects. For example, norovirus is highly contagious, particularly in settings where people are in close contact, such as crowded or close-contact settings, such as cruise ships or communal living environments. It is transmitted through consuming contaminated food or water and can spread easily from person to person. 

“Infectious Disease” broadly refers to diseases caused by infectious agents like bacteria, viruses, fungi, or parasites. It encompasses conditions resulting from invading and multiplying these microorganisms within the body. Infectious diseases can be transmitted through various means, including direct or indirect contact, vectors, or contaminated food and water. For example, Salmonellosis is caused by the bacterium Salmonella. It involves the invasion and multiplication of Salmonella bacteria within the digestive system. It is an infectious disease because the bacteria invade and multiply within the digestive system after consuming contaminated food, leading to symptoms like diarrhea and abdominal cramps. 

Meanwhile, “Communicable Disease” is a broader term that includes contagious and infectious diseases. A communicable disease can be transmitted from an infected person, animal, or object to another individual, leading to the spread within a community. It encompasses a wide range of contagious and infectious agents and modes of transmission. For example, Hepatitis A is a communicable disease. It is communicable, indicating that it can be transmitted from one person to another, often through consuming contaminated food or water, as it can be transmitted from person to person through the ingestion of contaminated food or water. The virus affects the liver, and infected individuals can spread the virus to others. 

Therefore, all contagious diseases are infectious, but not all infectious diseases are necessarily highly contagious. The level of contagion depends on the mode of transmission and how easily the infectious agent can be passed from one individual to another. The terms are often used interchangeably, but understanding their nuances helps convey specific aspects of disease transmission. In practice, the identification and classification of foodborne diseases would depend on what you want to emphasize in your mind.

About the author: Dr. Davis W. Cheng is a distinguished Supervisory Consumer Safety Inspector who contributes his expertise to the FSIS-OFO-Philadelphia District. Cheng majored in Agriculture and Biological Sciences. He earned a Ph.D. in Animal Genetics and Genetic Engineering. Cheng embarked on his professional journey in 2007 as a GS11 Biologist with the USDA. He engaged in genetic and pathological research. Over the years, he has transitioned through roles such as scientist, assistant/associate research professor, and senior scientist. Notable accolades include recognition from Agriculture and Agri-Food Canada for exceptional plant genome research in 2020, acknowledgment by former President George W. Bush for service to U.S. Veterans Affairs, and commendations from USDA Headquarters for outstanding job performance from 2018 to 2024. Cheng’s influence reaches beyond academia into practical applications, as evidenced by his involvement in developing or correcting business HACCP plans, SSOPs, and standards. He has played a pivotal role in solving public health and food safety challenges on the frontlines. In recent years, Cheng has assumed leadership in ensuring food and health safety in the USDA Food Safety and Inspection Service, particularly in poultry, meat, egg products, and other Ready-to-Eat (RTE) production plants.

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