3.3 Infectious Diseases

Question 1

Which serum antibody response usually characterizes the primary (early) stage of syphilis?
A. Antibodies against syphilis are undetectable
B. Detected 1 to 3 weeks after appearance of the primary chancre
C. Detected in 50% of cases before the primary chancre disappears
D. Detected within 2 weeks after infection

Answer 1

B. Detected 1 to 3 weeks after appearance of the primary chancre

During the primary stage of syphilis, about 90% of patients develop antibodies between 1 and 3 weeks after the appearance of the primary chancre.

Question 2

What substance is detected in the sample by the rapid plasma reagin (RPR) and Venereal Disease Research Laboratory (VDRL) tests for syphilis?
A. Cardiolipin
B. Anticardiolipin antibody (ACA)
C. Anti-Treponema pallidum antibody
D. T. pallidum

Answer 2

B. Anticardiolipin antibody (ACA)

Question 3

What type of antigen is used in the RPR card test?
A. Live treponemal organisms
B. Killed suspension of treponemal organisms
C. Cardiolipin
D. Tanned sheep cells

Answer 3

C. Cardiolipin

Cardiolipin is extracted from animal tissues, such as beef hearts, and attached to carbon particles. In the presence of reagin, the particles will agglutinate.

Question 4

Which of the following is the most sensitive test to detect congenital syphilis?
A. VDRL
B. RPR
C. T.pallidum particle agglutination (TP-PA)
D. Polymerase chain reaction (PCR)

Answer 4

D. Polymerase chain reaction (PCR)

PCR will amplify a very small amount of DNA from T.pallidum and allow for the detection of the organism in the infant. Antibody tests, such as VDRL and RPR, may detect maternal antibody only and do not indicate if the infant has been infected.

Question 5

A biological false-positive reaction is least likely with which test for syphilis?
A. VDRL
B. TP-PA
C. RPR
D. All are equally likely to yield a false-positive result

Answer 5

B. TP-PA

The TP-PA test is more specific for T.pallidum compared with nontreponemal tests, such as the VDRL and RPR tests, and would be the least likely to yield a biological false-positive result. Nontreponemal tests have a biological false-positive rate of 1% to 10% depending on the patient population tested. False-positive findings are caused commonly by infectious mononucleosis (IM), SLE, viral hepatitis, and human immunodeficiency virus (HIV) infection.

Question 6

A 12 year old girl has symptoms of fatigue and localized lymphadenopathy. Laboratory tests reveal peripheral blood lymphocytosis, positive RPR, and positive spot test for IM. What test should be performed next?
A. HIV screen
B. VDRL
C. Epstein-Barr virus (EBV)-specific antigen test
D. TP-PA test

Answer 6

D. TP-PA test

The patient’s symptoms are nonspecific and could be attributed to many potential causes. However, the patient’s age, lymphocytosis, and serological results point to IM. The rapid spot test for antibodies seen in IM is highly specific. The EBV-specific antigen test is more sensitive but is unnecessary when the spot test is positive. HIV infection is uncommon at this age and is often associated with generalized lymphadenopathy and a normal or reduced total lymphocyte count. IM antibodies are commonly implicated as a cause of biological false-positive nontreponemal test results for syphilis. Therefore, a treponemal test for syphilis should be performed to document this phenomenon in this case.

Question 7

Which test is most likely to be positive in the tertiary stage of syphilis?
A. Treponemal-specific antibody
B. RPR
C. VDRL
D. Reagin screen test (RST)

Answer 7

A. Treponemal-specific antibody

A treponemal-specific antibody test is more likely to be positive compared with a nontreponemal test in the tertiary stage of syphilis. In some cases, systemic lesions have subsided by the tertiary stage, and the nontreponemal tests become seronegative. Although the treponemal-specific antibody test is the most sensitive test for tertiary syphilis, it will be positive in both treated and untreated cases.

Question 8

What is the most likely interpretation of the following syphilis serological results?

RPR: reactive; TP-PA: nonreactive

A. Neurosyphilis
B. Secondary syphilis
C. Syphilis that has been successfully treated
D. Biological false positive

Answer 8

D. Biological false positive

A positive reaction with nontreponemal antigen and a negative reaction with a treponemal antigen is most likely caused by a biological false-positive nontreponemal test result.

Question 9

Which specimen is the sample of choice to evaluate latent or tertiary syphilis?
A. Serum sample
B. Chancre fluid
C. Cerebrospinal fluid (CSF)
D. Joint fluid

Answer 9

C. Cerebrospinal fluid (CSF)

Latent syphilis usually begins after the second year of untreated infection. In some cases, the serological tests become negative. However, if neurosyphilis is present, CSF serology will be positive and the CSF will display increase protein and pleocytosis characteristic of central nervous system infection.

Question 10

Interpret the following quantitative RPR test results

RPR titer: weakly reactive—1:4; reactive—1:8 to 1:64

A. Excess antibody, prozone effect
B. Excess antigen, postzone effect
C. Equivalence of antigen and antibody
D. Impossible to interpret; testing error

Answer 10

A. Excess antibody, prozone effect

This patient may be in the secondary stage of syphilis and is producing large amounts of antibody to T.pallidum sufficient to cause a prozone reaction as a result of antibody excess in the test. The test became strongly reactive only after the antibody was diluted.

Question 11

Tests to identify infection with HIV fall into which three general classification types of tests?
A. Tissue culture, antigen, and antibody tests
B. Tests for antigens, antibodies, and nucleic acid
C. DNA probe, DNA amplification, and Western blot tests
D. ELISA, Western blot, and Southern blot tests

Answer 11

B. Tests for antigens, antibodies, and nucleic acid

Question 12

Which tests are considered screening tests for HIV?
A. ELISA, chemiluminescent, and rapid antibody tests
B. IFA, Western blot, radioimmunoprecipitation assay
C. Culture, antigen capture assay, DNA amplification
D. Reverse transcriptase and messenger RNA (mRNA) assay

Answer 12

A. ELISA, chemiluminescent, and rapid antibody tests

Question 13

Which test are the recommended confirmatory tests for HIV?
A. ELISA and rapid antibody tests
B. HIV-1,2 antibody differentiation assays, and qualitative PCR test
C. Culture, antigen capture assay, quantitative PCR
D. Reverse transcriptase and mRNA assay

Answer 13

B. HIV-1,2 antibody differentiation assays, and qualitative PCR test

Question 14

How do fourth- and fifth-generation HIV tests reduce the time from infection to the test becoming positive?
A. They are PCR tests detecting viral RNA
B. They detect p24 antigen in addition to HIV antibody
C. They detect proviral DNA
D. They detect antibodies to more antigens than earlier generations of HIV tests

Answer 14

B. They detect p24 antigen in addition to HIV antibody

Question 15

A woman who has had five pregnancies subsequently tests positive for HIV on a fourth-generation assay and is negative on an HIV-1,2 differentiation assays and a follow up molecular assay. The initial reactivity may be caused by:
A. Possible cross-reaction with herpes or EBV antibodies
B. Interference from medication
C. Cross-reacting antibodies elicited during pregnancy
D. Possible technical error; a repeat specimen should be requested

Answer 15

C. Cross-reacting antibodies elicited during pregnancy

Question 16

Interpret the following results for HIV testing:

Fourth-generation ELISA: positive; repeat ELISA: positive; HIV 1,2 antibody differentiation assays: negative; qualitative HIV RNA rtPCR assay: positive

A. False-positive fourth-generation assay
B. False-negative antibody differentiation assay
C. Indeterminate; further testing indicated
D. HIV p24 antigen detected on fourth-generation ELISA

Answer 16

D. HIV p24 antigen detected on fourth-generation ELISA

Question 17

** What is the most likely explanation when antibody tests for HIV are negative but the PCR test is positive?**
A. Probably not HIV infection
B. Patient is in the “window phase” before antibody production
C. Tests were performed incorrectly
D. Clinical signs may be misinterpreted

Answer 17

B. Patient is in the “window phase” before antibody production

Question 18

What criteria constitute the classification system for HIV infection?
A. CD4-positive T-cell count and clinical symptoms
B. Clinical symptoms, condition, duration, and strength of reactivity on a fourth-generation HIV test
C. Presence or absence of lymphadenopathy
D. Strong fourth-generation HIV test reactivity and CD8-positive T-cell count

Answer 18

A. CD4-positive T-cell count and clinical symptoms

Question 19

What is the main difficulty associated with the development of an HIV vaccine?
A. The virus has been difficult to culture; antigen extraction and concentration are extremely laborious
B. Human trials cannot be performed
C. Different strains of the virus are genetically diverse
D. Anti-idiotype antibodies cannot be developed

Answer 19

C. Different strains of the virus are genetically diverse

Question 20

Which CD4: CD8 ratio is most likely in a patient with AIDS?
A. 2:1
B. 3:1
C. 2:3
D. 1:3

Answer 20

D. 1:3

Question 21

What is the advantage of fourth-generation rapid HIV tests over earlier rapid HIV tests?
A. They use recombinant antigens
B. They detect multiple strains of HIV
C. They detect p24 antigen
D. They are quantitative

Answer 21

C. They detect p24 antigen

Question 22

Which method is used to test for HIV infection in infants who are born to HIV-positive mothers?
A. ELISA
B. Western blot test
C. PCR test
D. Viral culture

Answer 22

C. PCR test

Question 23

What is the most likely cause when a fourth-generation HIV assay is positive for all controls and samples?
A. Improper pipetting
B. Improper washing
C. Improper addition of sample
D. Improper reading

Answer 23

B. Improper washing

Question 24

What constitutes a diagnosis of viral hepatitis?
A. Abnormal test results for liver enzymes
B. Clinical signs and symptoms
C. Positive results for hepatitis markers
D. All of these options

Answer 24

D. All of these options

Question 25

Which of the following statements regarding infection with hepatitis D virus (HDV) is true?
A. Occurs in patients with HIV infection
B. Does not progress to chronic hepatitis
C. Occurs in patients with hepatitis B virus (HBV) infection
D. Is not spread through blood or sexual contact

Answer 25

C. Occurs in patients with hepatitis B virus (HBV) infection

Question 26

All of the following hepatitis viruses are spread through blood or blood products except:
A. Hepatitis A virus (HAV)
B. HBV
C. HCV
D. HDV

Answer 26

A. Hepatitis A virus (HAV)

Question 27

Which hepatitis B marker is the best indicator of early acute infection?
A. Hepatitis B surface antigen (HBsAg)
B. Hepatitis B e-antigen (HBeAg)
C. Hepatitis B core antibody (anti-HBc)
D. Hepatitis B surface antibody (anti-HBs)

Answer 27

A. Hepatitis B surface antigen (HBsAg)

Question 28

Which is the first antibody detected in serum after infection with HBV?
A. Anti-HBs
B. Anti-HBc IgM
C. Anti-HBe
D. All are detectable at the same time

Answer 28

B. Anti-HBc IgM

Question 29

Which antibody persists in low-level carriers of HBV?
A. IgM anti-HBc
B. IgG anti-HBc
C. IgM anti-HBe
D. IgG anti-HBs

Answer 29

B. IgG anti-HBc

Question 30

What is the most likely explanation when a patient has clinical signs of viral hepatitis but tests negative for HAV IgM, HBsAg, and HCV antibody?
A. Tests were performed improperly
B. The patient does not have hepatitis
C. The patient may be in the “core window”
D. Clinical evaluation was performed improperly

Answer 30

C. The patient may be in the “core window”

Question 31

Which hepatitis B markers should be performed on blood products?
A. HBsAg and anti-HBc
B. Anti-HBs and anti-HBc
C. HBeAg and HBcAg
D. Anti-HBs and HBeAg

Answer 31

A. HBsAg and anti-HBc

Question 32

Which hepatitis antibody confers immunity against reinfection with HBV?
A. Anti-HBc IgM
B. Anti-HBc IgG
C. Anti-HBe
D. Anti-HBs

Answer 32

D. Anti-HBs

Question 33

Which test, other than serological markers, is most consistently elevated in viral hepatitis?
A. Antinuclear antibodies
B. Alanine aminotransferase (ALT)
C. Absolute lymphocyte count
D. Lactate dehydrogenase

Answer 33

B. Alanine aminotransferase (ALT)

Question 34

If only anti-HBs is positive, which of the following can be ruled out?
A. HBV vaccination
B. Distant past infection with HBV
C. Hepatitis B immune globulin (HBIG) injection
D. Chronic HBV infection

Answer 34

D. Chronic HBV infection

Persons with chronic HBV infection show a positive test result for anti-HBc (IgG or total) and HBsAg but not anti-HBs. Patients with active chronic hepatitis have not become immune to the virus.

Question 35

Interpret the following results for EBV infection: IgG and IgM antibodies to viral capsid antigen (VCA) are positive.

A. Infection in the past
B. Infection with a mutual enhancer virus, such as HIV
C. Current infection
D. Impossible to interpret; need more information

Answer 35

C. Current infection

Question 36

Rapid mono tests use latex particles coated with which of the following?
A. Guinea pig antigen
B. Beef proteins
C. Horse proteins
D. Sheep proteins

Answer 36

B. Beef proteins

Question 37

Blood products are tested for which virus before being transfused to newborns?
A. EBV
B. Human T-lymphotropic virus II (HTLV-II)
C. CMV
D. HDV

Answer 37

C. CMV

CMV can be life threatening if transmitted to a newborn through a blood product. HTLV-II is a rare virus, which like HIV, is a T-cell tropic RNA retrovirus. The virus has been associated with hairy cell leukemia, but this is not a consistent finding.

Question 38

What is the endpoint for the antistreptolysin O (ASO) latex agglutination assay?
A. Highest serum dilution that shows no agglutination
B. Highest serum dilution that shows agglutination
C. Lowest serum dilution that shows agglutination
D. Lowest serum dilution that shows no agglutination

Answer 38

B. Highest serum dilution that shows agglutination

Question 39

A streptozyme test was performed, but the result was negative, even though the patient showed clinical signs of a streptococcal throat infection. What should be done next?

A. Either ASO or anti-deoxyribonuclease B (anti-DNase B) test
B. Another streptozyme test using diluted serum
C. Antihyaluronidase test
D. Wait for 3 to 5 days and repeat the streptozyme test

Answer 39

A. Either ASO or anti-deoxyribonuclease B (anti-DNase B) test

The streptozyme test is used for screening and contains several of the antigen associated with streptococcal products. Because some patients produce an antibody response to a limited number of streptococcal products, bo single test is sufficiently sensitive to rule out infection. Clinical sensitivity is increased by performing additional tests when initial results are negative. The streptozyme test generally yields more false-positive and false-negative results compared with the ASO and anti-DNAse B tests. A positive result occurs in a smaller number of patients with recent streptococcal infections in the antihyaluronidase test compared with the ASO and anti-DNase B tests.

Question 40

Rapid assays for influenza that utilize specimens obtained from nasopharyngeal swabs detect:

A. IgM anti-influenza
B. IgA anti-influenza
C. IgA–influenza antigen immune complexes
D. Influenza nucleoprotein antigens

Answer 40

D. Influenza nucleoprotein antigens

Question 41

How can interfering cold agglutinins be removed from a test sample?

A. Centrifuge the serum and remove the top layer
B. Incubate the clot at 1°C to 4°C for several hours and then remove the serum
C. Incubate the serum at 56°C in a water bath for 30 minutes
D. Use an anticoagulated sample

Answer 41

B. Incubate the clot at 1°C to 4°C for several hours and then remove the serum

Cold agglutinins will attach to autologous RBCs if incubated at 1 C to 4 C. The absorbed serum will be free of cold agglutinins.

Question 42

All tubes (dilutions) except the negative control are positive for cold agglutinins. This indicates:
A. Contaminated RBCs
B. A rare antibody against RBC antigens
C. The sample was stored at 4°C prior to separating serum and cells
D. Further serial dilution is necessary

Answer 42

D. Further serial dilution is necessary

Question 43

All positive cold agglutinin tubes remain positive after 37°C incubation except the positive control. What is the most likely explanation for this situation?

A. High-titer cold agglutinins
B. Contamination of the test system
C. Antibody other than cold agglutinins
D. Faulty water bath

Answer 43

C. Antibody other than cold agglutinins

Question 44

Which increase in antibody titer (dilution) best indicates an acute infection?
A. From 1:2 to 1:8
B. From 1:4 to 1:16
C. From 1:16 to 1:256
D. From 1:64 to 1:128

Answer 44

C. From 1:16 to 1:256

A fourfold (two-tube) or greater increase in antibody titer is usually indicative of an acute infection.

Question 45

Which of the following positive antibody tests may be an indication of recent vaccination or early primary infection for rubella in a patient with no clinical symptoms?
A. Only IgG antibodies positive
B. Only IgM antibodies positive
C. Both IgG and IgM antibodies positive
D. Fourfold rise in titer for IgG antibodies

Answer 45

B. Only IgM antibodies positive

Question 46

Why is laboratory diagnosis difficult in cases of Lyme disease?

A. Clinical response may not be apparent upon initial infection; IgM antibody may not be detected until 3 to 6 weeks after the infection
B. Laboratory tests may be designed to detect whole Borrelia burgdorferi, not flagellar antigen found early in infection
C. Most laboratory tests are technically demanding and lack specificity
D. Antibodies formed initially to B. burgdorferi may cross react in antigen tests for autoimmune diseases

Answer 46

A. Clinical response may not be apparent upon initial infection; IgM antibody may not be detected until 3 to 6 weeks after the infection

Question 47

Serological tests for which disease may give a false-positive result if the patient has Lyme disease?

A. HIV
B. Syphilis
C. EBV
D. Hepatitis C

Answer 47

B. Syphilis

Question 48

In monitoring a patient with HIV infection, which parameter may be expected to be the most sensitive indicator of the effectiveness of antiretroviral treatment?

A. HIV antibody titer
B. CD4:CD8 ratio
C. HIV viral load
D. Absolute total T-cell count

Answer 48

C. HIV viral load

Question 49

A renal transplant recipient is found to have a rising creatinine level and reduced urine output. The physician orders a “urine PCR” assay. When you call to find out what organism the physician wants to identify, you are told:

A. HCV
B. Legionella pneumophila
C. EBV
D. BK virus

Answer 49

D. BK virus

Question 50

A newborn is to be tested for vertically transmitted HIV infection. Which of the
following tests is most useful?

A. HIV PCR
B. CD4 count
C. Rapid HIV antibody test
D. HIV IgM antibody test

Answer 50

A. HIV PCR

Question 51

Which of the following fungal organisms is best diagnosed by an antigen detection test as opposed to an antibody detection assay?

A. Histoplasma
B. Cryptococcus
C. Candida
D. Aspergillus

Answer 51

B. Cryptococcus

Question 52

Your cytology laboratory refers a Papanicolaou smear specimen to you for an assay designed to detect the presence of a virus associated with cervical cancer. You perform:

A. An ELISA for anti-human simplex virus 2 (anti-HSV-2) antibodies
B. A molecular assay for HSV-2
C. An ELISA for human papilloma virus (HPV) antibodies
D. A molecular assay for HPV

Answer 52

D. A molecular assay for HPV

Question 53

An immunosuppressed patient has unexplained anemia. The physician suspects a parvovirus B19 infection. The parvovirus IgM test result is negative. The next course of action is to tell the physician that:

A. The patient does not have parvovirus
B. A convalescent specimen is recommended in 4 weeks to determine if a fourfold rise in titer has occurred
C. A parvovirus PCR is recommended
D. A recent transfusion for the patient’s anemia may have resulted in a false-negative result and the patient should be retested in 4 weeks

Answer 53

C. A parvovirus PCR is recommended