Microbiology and the Chain of Infection Practice Questions

25 multiple-choice questions on Microbiology and the chain of infection for paramedic and EMT students, from Chapter 27 (Infectious Diseases). Read each question, pick your answer, then tap Show answer to check it and read the explanation.

25 practice questions

1. Several picnic guests start vomiting 2 hours after eating potato salad left in the sun. The very short onset suggests:

   1. A. A toxin already formed in the food
   2. B. A viral infection spreading person to person
   3. C. A parasite that needs weeks to mature
   4. D. Bacteria growing in the blood
   Show answer

   Answer: A. A toxin already formed in the food

   Symptoms within a few hours point to a preformed toxin, such as Staphylococcus aureus toxin in food left warm. Infections that must multiply in the body, viruses spreading between people, or parasites take a day or more to cause illness. Treatment is supportive, with attention to dehydration.

2. A communicable disease is one that:

   1. A. Is caused by bacteria rather than viruses
   2. B. Can spread person to person
   3. C. Is limited to the immune system
   4. D. Cannot be prevented by vaccines
   Show answer

   Answer: B. Can spread person to person

   Not all infections are communicable. Tetanus, for example, comes from the environment.

3. Bacteria growing on a long-term IV catheter are often hard to clear with antibiotics because they:

   1. A. Turn into viruses on the plastic
   2. B. Cannot survive outside the blood
   3. C. Form a protective biofilm layer
   4. D. Change into harmless normal flora
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   Answer: C. Form a protective biofilm layer

   Bacteria on catheters, ports, and implants build a slimy biofilm that shields them from antibiotics and white cells. That is why an infected line often has to be removed. Bacteria do not become viruses or flora, and they survive well on plastic.

4. A child recovered from norovirus 5 days ago and feels fine. Regarding spread to others, the family should know that:

   1. A. Recovery ends all risk of spread to others
   2. B. Spread is mainly by the airborne route
   3. C. Kissing is the main route
   4. D. Virus can still be shed in stool
   Show answer

   Answer: D. Virus can still be shed in stool

   People can shed norovirus in their stool for 2 weeks or more after they feel better, so careful hand washing with soap and water must continue. It spreads by the fecal-oral route and from vomit, not as an airborne disease.

5. The links in the chain of infection, in order, are:

   1. A. Host, agent, entry, exit, reservoir, transmission
   2. B. Agent, reservoir, exit, transmission, entry, host
   3. C. Reservoir, host, agent, entry, exit, transmission
   4. D. Transmission, entry, agent, host, exit, reservoir
   Show answer

   Answer: B. Agent, reservoir, exit, transmission, entry, host

   Breaking any link stops the spread of infection.

6. A day care center has an outbreak of diarrhea among toddlers. Which practice most likely spread it?

   1. A. Children sharing crayons during art time
   2. B. Open windows in the room during nap time
   3. C. Mosquitoes breeding in the outdoor play yard
   4. D. Poor hand washing after diaper changes
   Show answer

   Answer: D. Poor hand washing after diaper changes

   Diarrheal illnesses in day care spread by the fecal-oral route, mainly from hands contaminated during diaper changes and toileting. Hand washing with soap and water and cleaning changing surfaces break the chain. Shared crayons play a minor role, and open windows and mosquitoes do not spread diarrhea.

7. Studies find MRSA and other bacteria on many EMS stethoscopes. The best practice is to:

   1. A. Disinfect the diaphragm between patients
   2. B. Clean it once at the end of each 24-hour shift
   3. C. Keep it in a pocket between calls
   4. D. Replace it with a brand-new one once each year
   Show answer

   Answer: A. Disinfect the diaphragm between patients

   A stethoscope touches patient after patient and acts as a fomite. Wiping the diaphragm and tubing with an approved disinfectant between patients breaks this route. Cleaning once a shift or storing it in a pocket does nothing for the next patient.

8. Wiping down the stretcher rails between patients breaks which link in the chain of infection?

   1. A. The pathogen's reservoir host
   2. B. The original infectious agent
   3. C. The mode of transmission
   4. D. The next host's susceptibility
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   Answer: C. The mode of transmission

   Contaminated surfaces carry germs from one patient to the next, which is the mode (route) of transmission. Cleaning them interrupts that link. Vaccination targets host susceptibility, and treating an infected patient targets the agent or reservoir.

9. Asking a coughing patient to wear a surgical mask mainly blocks which link in the chain of infection?

   1. A. The portal of entry
   2. B. The reservoir itself
   3. C. The infectious agent
   4. D. The portal of exit
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   Answer: D. The portal of exit

   Respiratory germs leave an infected person through the mouth and nose. A mask on the patient traps droplets at that portal of exit. Your own mask or respirator protects your portal of entry.

10. A hospital places a patient with suspected tuberculosis in a negative-pressure room. This room design:

    1. A. Kills TB bacteria in the patient's lungs
    2. B. Lets staff skip their N95 respirators
    3. C. Keeps room air from flowing into the hall
    4. D. Raises oxygen levels in the patient's room
    Show answer

    Answer: C. Keeps room air from flowing into the hall

    In an airborne infection isolation room, air is drawn into the room and exhausted outside or through filters, so airborne particles cannot drift into the hallway. Staff entering still need an N95. The room does not treat the infection or change oxygen levels.

11. Indirect contact transmission occurs through:

    1. A. Breathing in airborne nuclei
    2. B. Touching contaminated surfaces
    3. C. A needlestick from a patient
    4. D. A mosquito or tick bite
    Show answer

    Answer: B. Touching contaminated surfaces

    Hand hygiene and surface cleaning break this route.

12. A paramedic develops jaundice and is diagnosed with acute hepatitis B. When looking for the exposure, she should search a look-back window of about:

    1. A. Several weeks to months
    2. B. The last 24 to 48 hours
    3. C. The last three to four days
    4. D. The last seven to ten days
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    Answer: A. Several weeks to months

    Hepatitis B has a long incubation period, averaging about 90 days (range 60 to 150), so the exposure may have happened months earlier. Looking back 24 to 48 hours, three to four days, or seven to ten days would miss the exposure entirely.

13. A child with chickenpox attended school the day before her rash appeared. This matters because chickenpox:

    1. A. Spreads 1 to 2 days before the rash
    2. B. Spreads mainly once the scabs fall off
    3. C. Spreads just by touching the dried scabs
    4. D. Cannot spread before the fever begins
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    Answer: A. Spreads 1 to 2 days before the rash

    Varicella is contagious from about 1 to 2 days before the rash until all lesions have crusted. Classmates may already have been exposed. Crusted scabs are not infectious.

14. Candida auris is an emerging yeast that spreads in nursing homes and hospitals. It is a concern for EMS because it:

    1. A. Spreads mainly through mosquito bites
    2. B. Infects healthy young adults in particular
    3. C. Is easily killed by any alcohol-free wipe
    4. D. Resists many drugs and disinfectants
    Show answer

    Answer: D. Resists many drugs and disinfectants

    C. auris is often resistant to several antifungal drugs, lives on skin and surfaces for weeks, and is not killed by some common disinfectants. Use contact precautions and a disinfectant labeled for C. auris when transporting colonized patients. It spreads by contact, mostly among sick, long-term-care patients.

15. The infectious dose is:

    1. A. The dose of antibiotic needed to cure
    2. B. Pathogen amount needed to infect
    3. C. The number of days a patient is ill
    4. D. The amount of vaccine in each dose
    Show answer

    Answer: B. Pathogen amount needed to infect

    Some organisms, such as norovirus, need only a few particles to cause infection.

16. A hepatitis A outbreak is traced to a restaurant cook who never felt sick until after customers did. The best explanation is that:

    1. A. The virus spread through the air vents
    2. B. Customers caught it from the dishes' soap
    3. C. He shed virus before symptoms began
    4. D. He was immune and could not spread it
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    Answer: C. He shed virus before symptoms began

    People with hepatitis A shed the most virus in their stool in the 2 weeks before jaundice or other symptoms start, and some never get sick. Poor hand hygiene by a food handler during that window can cause an outbreak. Hepatitis A is fecal-oral, not airborne.

17. Which patient has a built-in route for germs to bypass the skin and enter the body?

    1. A. One with a healed surgical scar on the belly
    2. B. One wearing a plaster cast over intact skin
    3. C. One with a small tattoo from 5 years ago
    4. D. One with a long-term urinary catheter
    Show answer

    Answer: D. One with a long-term urinary catheter

    Indwelling devices such as urinary catheters, central lines, and feeding tubes give bacteria a direct path past the body's barriers, which is why device-related infections are common. Healed scars, casts on intact skin, and old tattoos do not breach the barrier.

18. Several children develop watery diarrhea after swimming at the same public pool, even though it is properly chlorinated. A likely cause is:

    1. A. Legionella in the pool water
    2. B. Swallowing heavily chlorinated water
    3. C. A chlorine-resistant parasite
    4. D. An airborne virus at the pool
    Show answer

    Answer: C. A chlorine-resistant parasite

    Cryptosporidium, a parasite spread when swimmers swallow water contaminated with stool, can survive in properly chlorinated water for days. It causes watery diarrhea that can last weeks. People with diarrhea should not swim. Legionella causes pneumonia, not watery diarrhea, and swallowing chlorinated water does not cause an outbreak of diarrhea lasting days.

19. Smallpox was eradicated, and measles could be, mainly because these viruses:

    1. A. Have no animal reservoir
    2. B. Are spread mainly by the bites of insects
    3. C. Cause mild illness
    4. D. Cannot survive outside the human body
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    Answer: A. Have no animal reservoir

    A disease that lives only in humans can be wiped out if enough people are vaccinated, because the virus has nowhere else to hide. Diseases with animal reservoirs, such as rabies, cannot be eradicated this way. Smallpox and measles are not insect-borne and are not mild.

20. A healthy hiker who recently visited Arizona has had fever, cough, and fatigue for 2 weeks. A regional infection to consider is:

    1. A. Lyme disease from deer ticks
    2. B. Valley fever (a soil fungus)
    3. C. Legionnaires disease from pools
    4. D. Hepatitis A from tap water
    Show answer

    Answer: B. Valley fever (a soil fungus)

    Coccidioidomycosis (Valley fever) is caused by a fungus in the soil of the southwestern US; spores are inhaled with dust and can cause a pneumonia-like illness in healthy people. It does not spread person to person. Lyme disease is uncommon in Arizona, and the other options do not fit.

21. Malaria is caused by:

    1. A. A DNA virus
    2. B. A protozoan
    3. C. A yeast fungus
    4. D. A prion
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    Answer: B. A protozoan

    Plasmodium protozoa are transmitted by mosquitoes.

22. Which term describes an infection acquired in a health care setting?

    1. A. Community-acquired
    2. B. Zoonotic transmission
    3. C. Health care-associated
    4. D. Vector-borne
    Show answer

    Answer: C. Health care-associated

    Health care-associated infections include catheter infections, ventilator pneumonia, and C. difficile.

23. A toddler has bloody diarrhea and fever. The family keeps backyard chickens, and she often plays with the chicks. A likely source is:

    1. A. Salmonella carried by the birds
    2. B. Avian influenza spread from the flock
    3. C. Histoplasmosis from the bird droppings
    4. D. Hepatitis A from their eggs
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    Answer: A. Salmonella carried by the birds

    Backyard poultry and reptiles often carry Salmonella without looking sick, and young children who handle them and then touch their mouths are commonly infected. Hand washing after contact prevents it. Bird flu and histoplasmosis mainly affect the lungs, and hepatitis A spreads from people, not from chickens or eggs.

24. Which statement about exposure versus infection is correct?

    1. A. Exposure leads to infection in most cases
    2. B. Infection can occur without exposure
    3. C. Exposure leads to symptoms in most cases
    4. D. Exposure does not always infect
    Show answer

    Answer: D. Exposure does not always infect

    Infection depends on the dose, the route, the pathogen's virulence, and the host's defenses.

25. A nursing home resident is colonized with carbapenem-resistant Enterobacterales (CRE). During transport, you should:

    1. A. Use airborne precautions and an N95 respirator
    2. B. Refuse transport until he has been treated
    3. C. Use contact precautions and clean well
    4. D. Give him oral antibiotics on scene first
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    Answer: C. Use contact precautions and clean well

    CRE are gut bacteria resistant to nearly all antibiotics. They spread on hands and surfaces, so gloves, a gown for contact with the patient, hand hygiene, and thorough cleaning of the stretcher are the key steps. They are not airborne, and colonization is not a reason to refuse transport.