Diagnostic Assays in Infectious Diseases

Question 1

viruses

Answer 1

• acellular
• non-living
• DNA or RNA
• protein capsid +/- envelope

Question 2

bacteria

Answer 2

• prokaryote
• DNA genome no nucleus
• cell membrane and cell wall (gram +/-)
• many but not all are free-living

Question 3

fungi

Answer 3

• eukaryotes
• DNA genome in the nucleus
• cell membrane and cell wall
• free- living

Question 4

protozoa

Answer 4

• eukaryote
• DNA genome in nucleus
• cell membrane only
• free living

Question 5

accuracy

Answer 5

telling the truth

Question 6

precision

Answer 6

telling the same story over and over again

Question 7

sensitivity

Answer 7

the extent to which the test is accurate for those who have the disease avoiding false negative

Question 8

specificity

Answer 8

the extent to which the test is accurate for those who do not have the disease avoiding false positive

Question 9

positive predictive value

Answer 9

extent to which positive test indicates person with disease

Question 10

negative predictive value

Answer 10

extent to which a negative test indicates absence of disease

Question 11

sensitivity of light microscopy, antigen testing, culture, and nucleic acid amplification tests

Answer 11

light microscopy < culture < antigen testing < nucleic acid amplification tests

Question 12

Immunoassays

Answer 12

ELISA, western blots, rapid immunochromatographic strip tests, and particle agglutination tests

Question 13

epitope

Answer 13

single smallest piece of pathogen that an antibody can recognize

Question 14

enzyme linked immunosorbent assay (ELISA)

Answer 14

1. antigen detection- starts with antibody
2. antibody detection starts with antigen
   sensitivity and specificity generally pretty good

Question 15

antigen detection tests are indicators of

Answer 15

current infection

Question 16

antibody detection tests are indicators of

Answer 16

past infection

Question 17

limitations of antibody detection tests

Answer 17

not all infections produce antibodies

Question 18

low organism burden

Answer 18

sensitivity

Question 19

potential detection of closely related organisms

Answer 19

specificity

Question 20

too little specimen

Answer 20

sensitivity

Question 21

low prevalence population

Answer 21

specificity

Question 22

In a low/high prevalence population the PPV is much lower meaning you need to do another test to decide to confirm

Answer 22

low

Question 23

nucleic acid amplification tests

Answer 23

• amplification
• molecular detection assays for bacteria, viruses, and eukaryotic pathogens
• targets microbial DNA or RNA
• more sensitive and specific
• quick

Question 24

nucleic acid amplification tests does/does not require live organisms

Answer 24

does not

Question 25

Advantages of NAAT versus culture

Answer 25

- increased sensitivity, less likely false negative - faster results = quicker treatment - contact tracing so could identify other potentially exposed people Faster NAAT results than culture, so quicker treatment of the patient is possible. Faster NAAT results, so contact tracing, if indicated, could identify other potentially exposed persons more quickly. More sensitive NAAT is less likely to yield a false negative result.

Question 26

Dis-Advantages of NAAT versus culture

Answer 26

- more expensive - requires technical expertise, could cause delay - can detect non-viable organisms and thus is limited as a test of cure NAAT is more expensive than culture. NAAT requires more technical expertise and may only be available at distant reference lab, thus delaying testing. NAAT can detect non-viable organisms, and thus is limited as a test-of-cure.

Question 27

T/F culture always works for every organism

Answer 27

false | some bugs cannot cultivate in vitro

Question 28

most mistakes in testing process occur in the | pre-analytical, analytical, or post analytical portion ?

Answer 28

pre-analytical

Question 29

antimicrobial susceptibility testing is based widely on in vitro/in vivo testing

Answer 29

in vitro

Question 30

1. In which of the following situations would a nucleic acid amplification test be most likely to produce a false positive result? A: 1 week after antibiotic treatment of a susceptible bacterial infection. B: 6 months after antibiotic treatment of a susceptible bacterial infection. C: during asymptomatic infection with a low organism burden. D: during symptomatic infection with a high organism burden. E: in a patient population with a high prevalence of infection.

Answer 30

A: 1 week after antibiotic treatment of a susceptible bacterial infection.

Question 31

``` 2. Antibiotic susceptibility testing in the clinical microbiology laboratory relies primarily on which of the following methods? A: culture B: microscopy C: nucleic acid amplification D: serology E: antigen detection ```

Answer 31

A: culture

Question 32

``` 3. Which of the following diagnostic tests would become positive at the earliest time during viral infection? A: viral nucleic acid amplification B: viral protein detection C: viral culture D: virus-specific IgM detection E: virus-specific IgG detection ```

Answer 32

A: viral nucleic acid amplification

Question 33

``` 4. If you were to use a highly sensitive (99%) and highly specific (99%) test to screen for detection of HIV infection among the general population in Orange County, NC, how would you interpret a positive result? A: it is very likely a true positive B: it is possibly a true positive C: it is definitely a true positive D: it is very likely a false positive E: it is possibly a false positive F: it is definitely a false positive ```

Answer 33

E: it is possibly a false positive

Question 34

5. In the scenario described above in Question 4, what would you do next as a physician receiving the positive test result? A: tell the patient s/he is HIV positive, and prescribe highly active antiretroviral therapy B: tell the patient s/he is HIV positive, but delay the start of antiretroviral therapy C: tell the patient s/he has a positive screening test, and order a confirmatory test D: do not tell the patient about the screening result, and order a confirmatory test

Answer 34

C: tell the patient s/he has a positive screening test, and order a confirmatory test