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What makes a guest sick: foodborne illness basics

Foodborne illness is sickness from food that carries a germ, or a poison a germ already left in it. NEHA lists it first among the PFH course topics, and with reason: almost every other rule in a kitchen, from the hand sink to the probe thermometer, exists to stop it.

  • ExamPFH
  • Topic weight13%
  • Questions here15
  • UpdatedOct 14, 2026
On this page 7 sections
  1. Four kinds of culprit
  2. Infection or intoxication
  3. The Big 6, and the guests who get hit hardest
  4. Germs and guests, your turn
  5. Foodborne illness, asked plainly
  6. Sources
  7. Go deeper on this topic

Four kinds of culprit

Bacteria
Single cells that multiply in food left warm. A few hours in the danger zone (41–135°F, 5–57°C) can turn a harmless count into a harmful one. Some of them leave toxins behind as they grow.
Viruses
They don't grow in food at all. They ride in on a sick worker's hands or on contaminated water, and it takes very little to make a guest sick. Norovirus and hepatitis A are the two the Food Code singles out.
Parasites
Small organisms that live inside an animal or in water and reach people through food. In the kitchen, cooking to the required internal temperature is the main defense.
Toxins
Poisons, not living things. Some come from bacteria, some occur naturally in certain fish, mushrooms or plants. Heat often leaves them intact, so keeping them out of the food is the only reliable fix.

Infection or intoxication

There are two ways food makes someone sick. With an infection, the guest swallows living germs that keep multiplying in the gut. Shigella carried on an unwashed hand works that way.

With an intoxication, the harm was done before the plate left the pass. Picture a pot of rice cooked at noon and left on the back counter until dinner. Bacillus cereus can grow in it and leave a toxin, and a quick flash in the wok later doesn't take that toxin back out. That's why time and temperature control matters even for food that gets reheated.

Germs also move from one surface to another long after cooking: a cutting board, a towel, a glove. That route has its own page, cross-contamination. Hazards that aren't germs at all, like chemicals and allergens, sit in the next topic, contamination and allergens.

The Big 6, and the guests who get hit hardest

The FDA Food Code names six pathogens a food employee has to report if diagnosed, because they spread easily through food and cause serious illness: norovirus, hepatitis A, Shigella, Shiga toxin-producing E. coli (STEC), Salmonella Typhi and nontyphoidal Salmonella (FDA Food Code 2022, 2-201.11). Each one, and what it means for a sick worker: the Big 6 pathogens.

Some guests have less room for error. The Food Code's term is a highly susceptible population: people who are immunocompromised, preschool-age children, or older adults, eating food served in a place that provides care, like a nursing home, a hospital or a child care center (1-201.10). Kitchens that feed them run stricter rules on sick workers and on some raw foods.

Germs and guests, your turn

A miss here usually means two germs got swapped in your head, so read the notes on both. For a mixed set across all eight topics, use the food handler practice test.

Each question is a chit, an order ticket. Answer it and it flips to show why every option is right or wrong.

0 right · 0 missed · 15 to go

  1. No. 01

    Which group is most susceptible to foodborne illness?

    Pick one. The chit flips to a note on every option.

    Notes on No. 01

    1. A

      Young children Correct: Young children's immune systems are still developing, so they sit in the high-risk group with older adults, pregnant women, and people with weakened immunity.

    2. B

      Middle-aged adults Middle-aged adults in normal health usually handle a small dose of germs better than toddlers or older adults.

    3. C

      Healthy adults Healthy adults are the baseline; a strong immune system often fights off a dose that would sicken a young child.

    4. D

      Teenagers Teenagers generally have mature immune systems and are not counted among the high-risk groups.

  2. No. 02

    What group is most at risk for severe complications from Listeria monocytogenes?

    Pick one. The chit flips to a note on every option.

    Notes on No. 02

    1. A

      College athletes Being young and fit lowers risk; athletes are not a Listeria risk group, though adults over 65 are.

    2. B

      Teenagers Teens are not a Listeria risk group; the ones to watch are pregnant women, newborns, older adults, and people with weak immunity.

    3. C

      Adult men Healthy adult men rarely get serious listeriosis unless they are older or have a weakened immune system.

    4. D

      Pregnant women Correct: Listeria can cross the placenta and cause miscarriage, stillbirth, or a very sick newborn, which is why pregnant women are told to avoid cold deli meat and raw-milk cheese.

  3. No. 03

    What is the primary difference between infection and intoxication in foodborne illness?

    Pick one. The chit flips to a note on every option.

    Notes on No. 03

    1. A

      Infection only comes from meat products; intoxication comes from produce Both kinds can come from any food; produce causes infections too, as Salmonella and E. coli outbreaks on greens show.

    2. B

      Infection occurs faster than intoxication because germs act right away It is usually the reverse: a pre-formed toxin can strike within hours, while an infection needs time for germs to multiply.

    3. C

      Infection: germs grow in the body; intoxication: a toxin already in the food Correct: In an infection the germs multiply inside you; in an intoxication a toxin from germs like S. aureus or B. cereus is already in the food.

    4. D

      Infection is more serious than intoxication and always needs a doctor Severity depends on the germ and the person, not the category; some intoxications, like botulism, can kill.

  4. No. 04

    What is the first sign that food may be contaminated with bacteria?

    Pick one. The chit flips to a note on every option.

    Notes on No. 04

    1. A

      A change in color on the surface Color changes usually point to spoilage, and food can look perfect while still carrying Salmonella.

    2. B

      A slimy or different texture Sliminess comes from spoilage organisms; the germs that make people sick rarely change texture.

    3. C

      A sour or bad smell when opened Odor comes from spoilage, while most pathogens add no smell at all, so the sniff test proves nothing.

    4. D

      There may be no visible signs Correct: Pathogens usually don't change how food looks, smells, or tastes, which is why time, temperature, and clean handling are the real controls.

  5. No. 05

    Which of these makes a foodborne illness more likely to be severe?

    Pick one. The chit flips to a note on every option.

    Notes on No. 05

    1. A

      The food's temperature at serving Serving temperature matters for growth before the meal, but once food is eaten, what counts is how many germs got in.

    2. B

      A larger dose of germs eaten Correct: A bigger dose of germs usually means worse illness, and people in high-risk groups, like young children and older adults, get sicker from smaller doses.

    3. C

      How fast the meal was eaten Eating fast or slow doesn't change how many germs get swallowed.

    4. D

      The time of day it was eaten The clock has nothing to do with it; a dose eaten at breakfast is as dangerous as one eaten at dinner.

  6. No. 06

    What should you do if you suspect a foodborne illness outbreak?

    Pick one. The chit flips to a note on every option.

    Notes on No. 06

    1. A

      Wait to see if more people get sick Waiting lets the same food keep reaching guests, and every hour of delay can add more cases.

    2. B

      Notify your supervisor immediately Correct: Your supervisor can pull the suspect food, keep samples, and call the health department, steps one worker can't take alone.

    3. C

      Continue working normally Working as usual means the source may still be on the line and more people may get sick.

    4. D

      Clean the kitchen yourself Cleaning on your own can destroy evidence investigators need; report first and let the manager decide.

  7. No. 07

    Which pathogen is commonly associated with raw eggs?

    Pick one. The chit flips to a note on every option.

    Notes on No. 07

    1. A

      Listeria Listeria is tied more to deli meats, soft cheeses, and smoked seafood than to raw eggs.

    2. B

      Salmonella Correct: Salmonella can be inside an intact shell egg, so eggs are cooked to 145°F for immediate service and 155°F if they will be hot-held.

    3. C

      E. coli E. coli O157:H7 is linked mainly to undercooked ground beef and contaminated produce, not eggs.

    4. D

      Norovirus Norovirus spreads mostly from sick workers' hands and from shellfish, not from eggs themselves.

  8. No. 08

    Which bacterial toxin cannot be destroyed by cooking?

    Pick one. The chit flips to a note on every option.

    Notes on No. 08

    1. A

      E. coli toxin E. coli illness comes mainly from live bacteria, and proper cooking kills them before they can cause harm.

    2. B

      S. aureus toxin Correct: Staph toxin is heat-stable, so once it forms, reheating won't make the food safe; keeping food out of 41–135°F is the real control.

    3. C

      Salmonella toxin Salmonella causes illness as a live infection, and cooking to the right temperature kills it.

    4. D

      Campylobacter toxin Campylobacter dies with proper cooking; the risk is undercooked poultry and cross-contamination, not a heat-proof toxin.

  9. No. 09

    Which parasitic infection is associated with undercooked pork?

    Pick one. The chit flips to a note on every option.

    Notes on No. 09

    1. A

      Trichinella spiralis Correct: Trichinella larvae live in the muscle of pork and wild game, and cooking pork to 145°F for 15 seconds kills them.

    2. B

      Cryptosporidium Cryptosporidium travels in contaminated water and on produce, not in pork.

    3. C

      Giardia Giardia also spreads through water and poor handwashing rather than undercooked meat.

    4. D

      Anisakis Anisakis is a worm found in raw or undercooked fish, which is why fish served raw is frozen first.

  10. No. 10

    What is the primary risk factor for Cyclospora contamination?

    Pick one. The chit flips to a note on every option.

    Notes on No. 10

    1. A

      Raw shellfish from warm waters Warm-water shellfish bring Vibrio, not Cyclospora.

    2. B

      Undercooked ground meat Ground meat is linked to E. coli and Salmonella; Cyclospora is a parasite carried on fresh produce.

    3. C

      Unpasteurized raw dairy Raw milk carries Listeria, Campylobacter, and E. coli, but Cyclospora outbreaks trace back to produce.

    4. D

      Contaminated water on produce Correct: Cyclospora reaches berries, herbs, and leafy greens through contaminated irrigation or wash water, so buying from approved sources is the main defense.

  11. No. 11

    Which pathogen produces spores that can survive cooking temperatures?

    Pick one. The chit flips to a note on every option.

    Notes on No. 11

    1. A

      Norovirus Norovirus is a virus, so it forms no spores; it spreads from sick workers' hands.

    2. B

      E. coli O157:H7 E. coli O157:H7 doesn't form spores and dies when ground beef reaches 155°F for 17 seconds.

    3. C

      Salmonella Enteritidis Salmonella Enteritidis doesn't form spores; cooking eggs and poultry to the right temperature kills it.

    4. D

      Clostridium perfringens Correct: C. perfringens spores survive cooking and wake up when big pots cool slowly, which is why food must drop from 135°F to 70°F within 2 hours.

  12. No. 12

    Which group of customers should be warned about consuming raw sprouts?

    Pick one. The chit flips to a note on every option.

    Notes on No. 12

    1. A

      Immunocompromised individuals Correct: Sprouts grow in warm, wet conditions where Salmonella and E. coli multiply, and people with weakened immune systems are the most likely to get severely ill.

    2. B

      Healthy teenagers and young adults Healthy young people can get sick from sprouts too, but they are not the high-risk group that needs a warning.

    3. C

      Athletes on high-protein diets Diet doesn't change the risk here; what matters is the strength of a person's immune system.

    4. D

      Adult men under age 50 Healthy adult men are not a high-risk group; age and immune status drive the warning.

  13. No. 13

    How should you respond if a customer reports finding a metal staple in their food?

    Pick one. The chit flips to a note on every option.

    Notes on No. 13

    1. A

      Collect the item and document the incident Correct: Keeping the staple and writing down what happened lets the manager trace the source and stop it from reaching another plate.

    2. B

      Tell the guest it came from the supplier Pointing at the supplier before anyone checks is a guess, and it doesn't find where the staple really came from.

    3. C

      Throw out the plate and the staple right away Tossing the plate destroys the evidence that would show how the staple got into the food.

    4. D

      Comp the meal and skip any report A free meal may calm the guest, but without a report the same hazard can turn up again.

  14. No. 14

    What should be the first action when suspecting intentional food contamination?

    Pick one. The chit flips to a note on every option.

    Notes on No. 14

    1. A

      Secure the suspected food Correct: Setting the food aside so no one can use it stops more people from eating it and keeps it for investigators; then tell the manager right away.

    2. B

      Throw the food in the dumpster Discarding the food destroys evidence the health department or police may need.

    3. C

      Call the local news station Reporters are not part of the response; the manager contacts the health department and law enforcement.

    4. D

      Keep serving and watch guests Serving more of a food that may have been tampered with puts more guests at risk.

  15. No. 15

    Which pathogen is most commonly associated with raw seafood?

    Pick one. The chit flips to a note on every option.

    Notes on No. 15

    1. A

      Listeria monocytogenes Listeria is a concern in ready-to-eat smoked fish, but raw shellfish are best known for Vibrio.

    2. B

      E. coli O157:H7 E. coli O157:H7 is mainly tied to undercooked ground beef and produce.

    3. C

      Vibrio vulnificus Correct: Vibrio vulnificus lives in warm coastal water and concentrates in raw oysters, where it can cause severe illness in people with liver disease or weak immunity.

    4. D

      Salmonella Enteritidis Salmonella Enteritidis is linked to eggs and poultry rather than raw seafood.

Foodborne illness, asked plainly

Does cooking make food safe from every germ?

Cooking to the right internal temperature kills most of them. It can't undo a toxin that formed while food sat warm, and it doesn't protect food that gets touched by a dirty hand or board after it's cooked.

Is an allergic reaction a foodborne illness?

No. A reaction to peanuts or sesame is the guest's immune system responding to a food protein, with no germ involved. Allergens have their own rules, on contamination and allergens.

Sources

Go deeper on this topic