Deck 20: Serologic and Molecular Detection of Bacterial Infections

Question 1

Why is testing for Cryptococcal antigen preferred over testing for antibodies?

A) This is usually not a humoral response to infection.
B) Immunocompromised patients do not produce antibody.
C) Subclinical infection can be detected.
D) all of the above

Answer 1

all of the above

Question 2

Which statement best describes antigenic variation seen in parasites?

A) The host immune system can respond more quickly.
B) Different parasites have different antigens.
C) Parasites can periodically change their surface antigens.
D) Parasites become sequestered in host cells.

Answer 2

Parasites can periodically change their surface antigens.

Question 3

All of the following may be drawbacks of antibody testing for fungal infections EXCEPT:

A) The patient is immunocompromised.
B) Serologic tests may not be positive at a particular stage of the disease.
C) Presence of antibodies may not indicate an active infection.
D) False-positive results occur often in patients with functioning immune systems.

Answer 3

False-positive results occur often in patients with functioning immune systems.

Question 4

What would be an advantage of using the tube precipitation test for diagnosis of infection with Coccidioides immitis?

A) It is good at detecting IgG antibodies.
B) It detects early IgM antibodies.
C) It is subject to cross-reactivity.
D) It is subject to anticomplementary reactions.

Question 5

When is antibody testing for Cryptococcal antibodies most useful?

A) in determining patient prognosis
B) in diagnosing immunocompromised patients
C) in ruling out the disease in young patients
D) as a screening test after exposure to the fungus

Question 6

The most likely reason for the development of an IgE antibody response in humans is:

A) protection against helminth infections
B) protection against bacterial diseases
C) protection against viruses
D) protection against allergens

Question 7

A host's immunological response to parasites includes all of the following EXCEPT:

A) formation of IgG,IgM,and IgA antibodies
B) production of cytokines
C) gamma-interferon production by natural killer cells
D) sequestering the parasite in host cells

Question 8

A 25-year-old pregnant female has serologic testing to determine if she has a toxoplasmosis infection.A low level of both IgM and IgG is found.On repeat testing 2 weeks later,the results are the same.What can be concluded from these results?

A) She has an active infection.
B) The baby will have serious central nervous system damage.
C) She was exposed to toxoplasmosis at some time in the past.
D) She has never been exposed to toxoplasmosis.

Question 9

A 30-year-old male patient with AIDS exhibits pulmonary symptoms that include coughing and some difficulty breathing.The patient reported that he had previously worked in a bakery.His white blood cell count was normal,indicating that the infection is not bacterial in nature.Tests for the presence of fungal antigens were performed with the following results: ouchterlony immunodiffusion negative for antibodies to Aspergillus; negative latex agglutination test for Candida antigen,and positive EIA test for the galactomannan antigen of Aspergillus.What conclusion can be reached from these results?

A) The galactomannan is a false-positive result.
B) The infection is likely caused by Aspergillus.
C) The Candida antigen test is a false-negative
D) An Aspergillus infection is ruled out due to negative antibody testing.

Question 10

In an individual with AIDS,what is the most likely reason for a toxoplasmosis infection that invades the central nervous system?

A) The host produces a lot of antibody.
B) Cysts in the tissue become reactivated.
C) The individual ingests contaminated water.
D) The parasite has acquired new surface proteins.