A foodborne illness (FBI) is any sickness that results from consuming food or drink contaminated with harmful bacteria, viruses, parasites, or chemical substances. While the initial infection is acquired through a food source, the agents that cause these illnesses are often capable of spreading beyond the original meal. Many common pathogens responsible for FBI can be easily transmitted from one person to another after the first individual becomes sick. This means that an outbreak originating from contaminated lettuce or undercooked meat can quickly turn into a person-to-person spread within a household or community setting.
Understanding Contagion Versus Contamination
The public often confuses the terms contamination and contagiousness when discussing foodborne illness, but they refer to two distinct transmission pathways. Contamination describes the initial event where food or water becomes tainted with an infectious agent or a toxic substance. For example, Salmonella bacteria on raw chicken cross-contaminating a cutting board used for vegetables is a pathway of primary food contamination.
Contagiousness, however, refers to secondary transmission, which is the ability of an infectious agent to spread from an already sick person to a healthy person. A key distinction is that only illnesses caused by living, infectious microorganisms, such as bacteria, viruses, or parasites, can be contagious. Illnesses caused by non-infectious agents, like toxins or heavy metals, cannot spread because the poison itself is not a living organism capable of multiplying in a new host.
Food poisoning from a bacterial toxin like Botulism or Scombroid poisoning is not contagious. Conversely, illnesses caused by microbes like Norovirus or certain strains of E. coli begin with food contamination but can continue to circulate through person-to-person contact. The term “foodborne” simply identifies the source of the initial outbreak, not the sole method of transmission.
How Secondary Spread Occurs
The primary mechanism for the person-to-person spread of foodborne pathogens is the fecal-oral route. This occurs when microscopic particles of feces containing the pathogen are transferred from an infected person to the mouth of a healthy person. Poor hand hygiene after using the restroom is the most common driver of this transmission.
Infectious agents are transferred to surfaces, known as fomites. High-touch objects like doorknobs, faucets, light switches, and shared electronics can harbor pathogens deposited by an infected person’s hands. A healthy person touches the contaminated surface and then touches their mouth, eyes, or nose, completing the infectious cycle.
Some pathogens, such as Norovirus, also spread through respiratory droplets or aerosols during bouts of explosive vomiting. The force of vomiting can aerosolize viral particles into the air, which then settle on nearby surfaces or are inhaled directly by others in the immediate vicinity. This airborne mechanism allows the pathogen to contaminate an area up to several feet away from the sick individual.
High-Risk Pathogens for Person-to-Person Spread
The risk of secondary transmission varies significantly depending on the specific microbe involved. Norovirus is the most highly contagious foodborne pathogen, often requiring an infectious dose as low as 18 viral particles to cause illness. This low threshold, combined with the copious shedding of the virus, estimated to be up to five billion infectious doses per gram of feces, makes it difficult to contain.
Infected individuals can continue to shed Norovirus in their stool for two weeks or more after their symptoms have completely resolved. Bacterial pathogens like Salmonella and Shiga toxin-producing E. coli (STEC) are also moderately contagious through the fecal-oral route.
People infected with Salmonella can shed the bacteria in their feces for weeks to months following their recovery from symptoms, prolonging the period of potential contagiousness. For STEC, the median duration of fecal shedding in children can be around 21 days.
In contrast, illnesses caused by toxins, rather than a living organism, are not contagious because the agent is a chemical poison that cannot replicate or multiply. Botulism, for instance, is caused by a neurotoxin produced by the bacterium Clostridium botulinum outside the body. The illness cannot be passed from the sick person to others.
Stopping the Spread at Home
Preventing secondary spread in a household requires infection control measures once symptoms appear. The most effective defense remains proper hand hygiene using soap and running water for at least twenty seconds, especially after using the toilet or assisting the sick person. Alcohol-based hand sanitizers are less effective against viruses like Norovirus, so they should not be used as a substitute for thorough hand washing.
Cleaning and disinfection of surfaces is important, focusing on high-touch areas such as door handles, remote controls, faucets, and toilet flush levers. A standard household bleach solution is often required for effective disinfection. A concentration of one-third cup of household bleach mixed into one gallon of water is effective on non-porous surfaces.
Any clothing, linens, or towels soiled by vomit or diarrhea must be handled carefully to prevent aerosolizing the virus by shaking the material. These items should be washed immediately with detergent on the longest cycle available using the hottest water setting. Machine drying on the highest heat setting is also necessary.