Intro to Infectious Disease Diagnosis

Question 1

Definition: Tissues and cells stained with “general” stains, then observed microscopically for general morphologic features

Answer 1

Histology/Cytology

• tissues=histology
• cells=cytology

Question 2

2 Advantages of Histology and Cytology

Answer 2

1. May be quick to perform

2. Allows observation of an an array of infectious and other (malignant, necrotic) process

Question 3

2 Disadvantages of Histology and Cytology

Answer 3

1. Not specific for any infecting organism or disease syndrome (no definitive disease diagnosis)
2. Requires considerable expertise to read (usually a pathologist)

Question 4

Definition: tissues and cells examined with the electron microscope

Answer 4

Electron Microscopy (EM)

Question 5

2 Advantages of Electron Microscopy

Answer 5

1. ultrastructure of organism can be observed

2. Good for viruses, etc, that cannot be diagnosed through other approaches

Question 6

2 Disadvantages of Electron Microscopy

Answer 6

1. expensive, requires expertise to perform/read

2. usually no definitive disease diagnosis

Question 7

Definition: tissues and cells assayed for the presence of unique organismal nucleic acid sequences. Routinely involves use of nucleic acid probes and nucleic acid amplification

Answer 7

Molecular Diagnostics

Question 8

For molecular diagnostics give example of a probe and example of amplification

Answer 8

Probes: Fluorescence in situ hybridization (FISH)
Amplification: Polymerase chain reaction (PCR)

Question 9

3 advantages of molecular diagnostics

Answer 9

1. very specific for a single type of organism
2. good for viruses, etc. that cannot be diagnosed through other applications
3. very sensitive when amplification is used

Question 10

3 Disadvantages of molecular diagnostics

Answer 10

1. Expensive
2. Cumbersome (but simplified methods are appearing)
3. Few FDA-cleared methods (but this is improving)

Question 11

Definition: cultivation of microorganisms in in vitro systems to allow organism(s) to replicate or grow, so they can be observed and characterized

Answer 11

Isolation in Culture

Question 12

2 Advantages of isolation in culture

Answer 12

1. Allows many types of organisms to be detected at the same time
2. not organism specific (an open system)

Question 13

3 Disadvantages of isolation in culture

Answer 13

1. slow
2. not useful for some organisms (that do NOT proliferate in in vitro systems)
3. organism viability required

Question 14

Definition: tissues and cells are assayed for the presence of unique organismal antigens

Answer 14

Antigen Detection

Question 15

When doing antigen detection, _____ indicates the identity of the antigen in the cells/tissues

Answer 15

Reactivity

Question 16

3 advantages of antigen detection

Answer 16

1. usually quick
2. provides definitive identification
3. organism viability is not required

Question 17

2 disadvantages of antigen detection

Answer 17

1. detects small amounts of infecting agent poorly compared to isolation in culture or molecular methods
2. detects only a single (or limited related group of) target antigen(s) at the same time

Question 18

Definition: indirect evidence of infection through detecting antibodies produced against the infecting agent. Assays are immunoserologic, involving reacting patients sera with known antigens. Patients antibodies react with their homologous antigen, thus identifying the unknown antibody

Answer 18

Serology (Antibody Detection)

Question 19

3 Advantages of serology

Answer 19

1. Good for detecting infections caused by organisms that are difficult to isolate in culture
2. Good for detecting infections caused by unsocial organisms (those that are not vaccinated against or acquired routinely EX: HIV)
3. Important when species for testing are difficult to collect (i.e. a brain biopsy)

Question 20

What sample is used when specimens for testing are difficult to collect (brain biopsy)

Answer 20

peripheral blood sample

Question 21

2 Disadvantages of serology

Answer 21

1. sometimes slow

2. may require comparison of antibody levels in two samples collected 2 weeks apart

Question 22

5 reasons that a definitive diagnosis is important for infectious diseases

Answer 22

1. Ensure appropriate therapy (eliminate unnecessary therapy)
2. Give patient realistic prognosis
3. Implement appropriate infection control measures
4. Education
5. Research