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U.S. Department of Health and Human Services


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List of Terms: E

Return to Comprehensive List of Terms



Did You Know?


About 50 years ago, there were only 5 known organisms that caused foodborne illness. Today, there are at least 25 known foodborne pathogens -- including 20 newly-discovered ones. There has been a phenomenal increase in these pathogens: Campylobacter jejuni, Yersinia enterocolitica, E. coli O157:H7, Vibrio cholerae, Listeria monocytogenes, and the noroviruses.




>  E. coli O157:H7 (see Escherichia coli O157:H7)   


> Emerging Pathogen
An illness-causing microorganism that is either:

  • previously unknown to be a human pathogen;
  • not expected to occur in a particular food;
  • has caused a dramatic increase in new cases of illness.

Food Safety Implication: Microorganisms continue to adapt and evolve, sometimes increasing in their ability to make an individual sick. Microorganisms previously not recognized as human pathogens or pathogens unexpectedly found in particular foods have caused outbreaks of foodborne illness. Some examples are Listeria monocytogenes, Escherichia coli O157:H7, and the parasite Cyclospora.

How Pathogens Emerge: Since the late 1970s, newly recognized foodborne pathogens have emerged worldwide. Some contributing factors for these emerging pathogens include:

  • The transfer of genetic material from pathogenic bacteria through transformation, transduction, and conjugation (see individual terms for definitions). These 3 processes can produce cells that are stronger and more resistant than the original bacterial cells. As a result, new bacterial strains are often resistant to antibiotics. For example, some strains of Salmonella species are now resistant to multiple important antimicrobial drugs. 
  • Our food system has changed. The United States now imports foods from all over the world. Some bacteria are commonly found in one part of the world, but not in others. When we import foods, we can also import the foodborne pathogens associated with the foods.


> Epidemiology
The study of the occurrence and causes of diseases or other health-related conditions, states, or events in specified populations. One of the chief functions of this study is to identify populations at high risk for a given disease, so that the cause may be known and preventive measures implemented.

Did You Know? 
E. coli O157:H7 was first recognized as a pathogen in 1982. This bacterium can also be transmitted from person to person. People who swim in pools contaminated with feces -- from a baby's diaper, for example -- can be infected with this organism.

> Escherichia coli O157:H7 (also known as Pathogenic E. coli) 
A bacterium that can produce a deadly toxin. Infections from E. coli O157:H7 are estimated at 73,000 cases per year.

E. coli O157:H7
E. coli O157:H7

While most E. coli are normal residents of our small intestine and aids in digestion and enable our bodies to create vitamin K, there are some strains, such as E. coli O157:H7, that can cause severe illness in people and animals.

Sources: Meat, especially undercooked or raw hamburger, uncooked produce, raw milk, unpasteurized juice, and contaminated water.


Incubation: Usually 3 to 4 days after ingestion, but may occur anywhere from 1 to 10 days after ingestion.

Symptoms: Often severe abdominal cramps, bloody diarrhea, and nausea. E. coli O157:H7 can also manifest as non-bloody diarrhea or be symptomless. In young children, the elderly, and people with weakened immune systems, this pathogen can cause kidney damage that can lead to death.

Duration: 5 to 8 days.


> Expiration Date
The calendar date on the packaging of a food that indicates the last date a food should be eaten or used. (Also see "Best If Used By," "Sell By," and "Use By" Dates.)

Food Safety Implication: Foods that are purchased or used after the expiration date could contain spoilage bacteria or pathogens and may not be safe to eat.

Food Safety Precautions:

  • Don't buy foods after the expiration date has passed. 
  • At home, throw out foods after the expiration date has passed.