Intro to Infectious Disease Diagnosis

Question 1

Tissues and cells stained w/ “general” stains, then observed microscopically for general morphologic features

Answer 1

Histology/cytology

• Tissues = histology
• Cells = cytology

Question 2

Histology/cytology

- Advantages

Answer 2

• May be quick to perform

- Allows observation of an arry of infectious and other (malignant, necrotic) process

Question 3

Histology/cytology

- Disadvantages

Answer 3

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

Question 4

Tissues and cells examined w/ an electron microscope

Answer 4

Electron microscopy (EM)

Question 5

Electron microscopy

- Advantages

Answer 5

• Ultrastructure of organism can be observed

- Good for viruses, etc., that can be diagnosed through other approaches

Question 6

Electron microscopy

- Disadvantages

Answer 6

• Expensive, requires expertise to perform/read

- Usually no definitive disease diagnosis

Question 7

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

Molecular diagnostics

- Give example of a probe and amplification

Answer 8

Probes: Fluorescence in situ Hybridization (FISH)
Amplification: Polymerase Chain Reaction (PCR)

Question 9

Molecular diagnostics

- Advantages

Answer 9

• Very specific for a single type of organism
• Good for viruses, etc., that cannot be diagnosed through other applications
• Very sensitive when amplification is used

Question 10

Molecular diagnostics

- Disadvantages

Answer 10

• Expensive
• Cumbersome (but simplified methods are appearing)
• Few FDA-cleared methods (but this is improving)

Question 11

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

Isolation in culture

- Advantages

Answer 12

• Allows many type of organisms to be detected at the same time
• Not organism specific (an open system)

Question 13

Isolation in culture

- Disadvantages

Answer 13

• Slow
• Not useful for some organisms (that do NOT proliferate in in vitro systems)
• Organism viability required

Question 14

Tissues and cells are assayed for the presence of unique organismal Ags

Answer 14

Ag detection

Question 15

When doing Ag detection, ____ indicates the identity of the Ag in the cells/tissues

Answer 15

Reactivity

Question 16

Ag detection

- Advantages

Answer 16

• Usually quick
• Provides definitive identification
• Organism viability is not required

Question 17

Ag detection

- Disadvantages

Answer 17

• Detects small amounts of infecting agent poorly compared to isolation in culture or molecular methods
• Detects only a single (or limited related group of) target Ag(s) at the same time

Question 18

Indirect evidence of infection through detecting Abs produced against the infecting agent;

• Assays are immunoserologic, involving reacting patients sera w/ known Ags
• Patient’s Abs react w/ their homologous Ag, thus identifying the unknown Ab

Answer 18

Serology/Ab detection

Question 19

Serology

- Advantages

Answer 19

• Good for detecting infections caused by organisms that are difficult to isolate in culture
• Good for detecting infections caused by unsocial organisms (those that are not vaccinated against or acquired routeinly (ex: HIV)
• 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

Serology

- Disadvantages

Answer 21

• Sometimes slow

- May require comparison of Ab levels in two samples collected 2 weeks apart

Question 22

5 reasons that a definitive diagnosis is important for infectious diseases

Answer 22

• Ensure appropriate therapy (eliminate unnecessary therapy)
• Give patient realistic prognosis
• Implement appropriate infection control measures
• Education
• Research