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Diagnostic Methods > Infectious Disease Microscopy And Diagnostics > Flashcards

Infectious Disease Microscopy And Diagnostics Flashcards

1
Q

What is a pathogen?

A

microorganism that causes infectious disease

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2
Q

What is normal flora?

A

Bacteria that reside in a part of the body normally and it doesn’t cause infection

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3
Q

What is contamination?

A

an unintended introduction of potentially infectious material into a sample of body fluid

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4
Q

What is colonization?

A

Colonies of an organism that takes up residence in a part of the body where it would normally live but does not cause pathologic infection

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5
Q

What is an infection?

A

the invasion and multiplication of microorganisms into a part of the body resulting in illness

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6
Q

What is a sterile site?

A

Body part that is meant to be free of organisms

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7
Q

What are examples of sterile fluid?

A

Urine

CSF

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8
Q

What are non-sterile sites?

A

Parts of the body that contain normal flora

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9
Q

What are examples of non-sterile sites?

A

mouth

colon

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10
Q

What are the 5 categories of medical microbiology Lab testing for infectious diseases?

A

1) Antigen detection
2) Direct stains/examination
3) Cultures (aerobic and anaerobic) = ID from positive cultures and susceptibility testing
4) Nucleic acid detection
5) Serology

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11
Q

What is a direct specimen?

A

Surgical or needle aspiration of site

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12
Q

What is an example of a direct specimen?

A

Skin abscess

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13
Q

What is an indirect specimen?

A

Must pass through site with normal flora

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14
Q

What is an example of an indirect specimen?

A

Expectorated sputum

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15
Q

What is a sample from site with normal flora?

A

Both pathogen and normal flora are in the same site

Stool is an example of this

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16
Q

What are the two types of antigen detection tests?

A

Direct Fluorescent Antibody (DFA)

Indirect Fluorescent Antibody (IFA)

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17
Q

What is DFA?

A

Fluorescent labeled antibody binds to antigen of interest on a glass slide or other surface

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18
Q

What is IFA?

A

Looking for patients own native antibody

Antibody with is NOT fluorescent labeled binds to antigen of interest on a glass slide or other surface; fluorescent labeled antibody to IgG is then added and binds to antibody previously bound to antigen

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19
Q

Why do we need to have an indirect antigen detection test?

A

The antibodies used in DFA are synthetically made and because antigens often change, there can be problems with those antibodies that were made, not binding to the antigen

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20
Q

What tests are used as antimicrobial sensitivity testing?

A

Dilution method

Disk diffusion method

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21
Q

What is the dilution method?

A

Organism is put into tubes and a serial concentration amount is put into different tubes

Tubes are allowed to incubate and then looked at to see which concentration of antimicrobial agent inhibited the most of the organism

Turbidity of organism

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22
Q

What is the disk diffusion method?

A

Organism is spread over agar plate

Disks with differing concentrations and differing antimicrobial agents are put onto agar plate

zone of clearance is then measured after incubation to see how sensitive the organism is to the antimicrobial agent

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23
Q

What is the minimum inhibitory concentration (MIC)?

A

lowest concentration of an antimicrobial agent that inhibits growth

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24
Q

What does sensitive mean?

A

Antimicrobial is effective at retarding the growth of that pathogen

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25
Q

What does intermediate mean?

A

organism has some resistance to the antimicrobial agent

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26
Q

What does resistant mean?

A

Avoid this because pathogen isn’t susceptible to antimicrobial agent

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27
Q

What is Nucleic acid amplification (NAAT) testing?

A

Highly sensitive and specific

Valuable for difficult to detect or grow organisms

ONLY DETECTS ORGNIAMS THE ASSAY DETECTS

Ex. = HIV viral load

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28
Q

What is imperative that you know before using NAAT?

A

You must know what organism you are looking for in order to use this test

If the pathogen is no longer present = no results

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29
Q

What are serological tests?

A

Detect host antibodies

Not detectable early in disease

Can represent previous infection

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30
Q

What anitbodies are found in early infection?

A

IgM

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31
Q

What antibodies are found in late infection?

A

IgG

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32
Q

What diseases can be evaluated with serological assays?

A 
Lyme disease
Hep A
Measles
Mumps
Varicella virus (chickenpox)
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33
Q

What is a strep throat test?

A

Detects Streptococcus pyogenes (Group A beta-hemolytic streptococcus)

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34
Q

What are the two types of strep throat tests?

A

1) Rapid antigen test

2) Throat culture

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35
Q

Which strep test is used more often?

A

Rapid antigen test

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36
Q

What is a rapid antigen detection test?

A

Detects Group A strep antigens using standard immunologic techniques

Results are available in 10-20 min. so patient can wait in office

90-95% Sensitivity
95-98% Specificity
This is only if sample is good

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37
Q

What should be done if a rapid antigen detection test comes back negative for strep throat?

A

A throat culture should be performed; although this does depend on the hospitals protocols

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38
Q

What is a throat culture?

A

Double swab of throat for strep

Culture is spread out on agar plate, incubated at a certain temp., and they wait for growth

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39
Q

What are blood cultures used for?

A

To detect bacteremia or fungemia

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40
Q

What diseases are blood cultures used to detect?

A 
Sepsis
Meningitis
Osteomyelitis
Arthritis 
Endocarditis 
Peritonitis 
Pneumonia
Fever of unknown origin
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41
Q

What are the disadvantages of a blood culture?

A

Even in patients with bacteremia, they are likely to have a low number of bacteria in their blood and numbers often fluctuate

Therefore, multiple sets must be taken with sufficient volume of blood

Contamination from ubiquitous normal flora is possible and careful interpretation must be employed when a positive results returns

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42
Q

What should you remember about blood cultures?

A

If you order a blood culture, you are committed to act on those results

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43
Q

When should blood cultures absolutely be obtained?

A

prior to antibiotic therapy

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44
Q

What are the characteristics of Gram + bacteria?

A

Thick murein layer

Stain dark purple

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45
Q

What are the characteristics of Gram - bacteria?

A

Outer membrane, thin murein layer, and inner membrane

Stain pink

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46
Q

What are examples of Gram + bacteria?

A

Staph epidermis
Strep pyogenes
Clostridium tetani

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47
Q

What are examples of Gram - bacteria?

A

E. coli
Salmonella typhi
Vibrio cholerae
Bordetella pertussis

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48
Q

What are diplococci?

A

Cocci in pairs

Neisseria Gonorrhoaea

Gonorrhea

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49
Q

What are streptococci?

A

Cocci in chains

Streptococcus pyogenes

Strep throat

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50
Q

What are staphylococci?

A

Cocci in clusters

Staph aureus

Boils

51
Q

What are tetrads?

A

A packet of 4 cocci

Micrococcus luteus

Rarely pathogenic

52
Q

What are octads?

A

A packet of 8 cocci

Sarcina ventriculi

Rarely pathogenic

53
Q

What are the different bacterial shapes?

A

Spheres
Rods
Spirals

54
Q

What are Vibrio spp. and Campylobacter spp.?

A

Gram - curved rods

55
Q

What is E. coli?

A

Gram - thin rods

56
Q

What is Acinetobacter spp.?

A

Gram variable coccobaccili

57
Q

What is Haemophilus?

A

Tiny gram -, pleomorphic diplococci

58
Q

What is strep pneumoniae?

A

Gram +, kidney shaped diplococci

59
Q

What is N. Gonorrhea?

A

Gram - intracellular diplococci

60
Q

What is staph?

A

Gram + cocci in clusters

61
Q

What is strep?

A

Gram + cocci in chains

62
Q

What are acute phase proteins/reactants?

A

Those proteins/entities whose serum concentrations increase or decrease by at least 25% during inflammatory states

Acute phase response accompanies both acute and chronic inflammatory states associated with infection , trauma, infarcation, inflammatory arthrides, and systemic autoimmune diseases

63
Q

What are the two Acute phase reactants?

A

1) Erythrocyte Sedimentation Rate (ESR)

2) C-reactive protein (CRP)

64
Q

What is the ESR?

A

The rate in mm/hr at which erythrocytes suspended in plasma settle when placed in a vertical tube

It is an indirect measure of the Acute phase response and acute phase proteins (fibrinogen), in patients with acute or chronic inflammation

65
Q

What is a function of CRP?

A

It binds phosphocholine which permits the recognition of both foreign pathogens that display this moiety and phospholipid constituents of damaged cells

66
Q

What conditions can cause an elevated ESR that are not related to acute or chronic inflammation?

A 
Increased age and female gender
Anemia
Renal disease
Obesity
Tilting of the ESR tube or high room temp.
67
Q

What conditions can cause a decrease in ESR that are not related to acute or chronic inflammation?

A 
Abnormalities of erythrocytes
Extreme leukocytosis
Extremely high serum bile salt levels
Heart failure
Hypofibrinogenemia
Cachexia
Clotting of sample
68
Q

What inflammatory conditions cause an increase in ESR?

A

Tissue injury
Ischemia
Trauma

69
Q

When do elevations of CRP typically occur?

A

In acute and chronic inflammation

70
Q

In what type of infections are CRP levels markedly increased and why?

A

Bacterial infections because bacteria have more phosphocholine than viruses

71
Q

What conditions can cause minor CRP elevations?

A 
Obesity
Cigarette smoking
Diabetes Mellitus
Uremia
Hypertension
Low levels of physical activity
72
Q

What are nontreponemal tests?

A

Tests for reagin antibodies

Based on the reactivity of serum from patients with syphillis to a cardiolipin cholesterol lecithin anitgen

Semi-quantitative = amount of antibody present reflects activity of infection

Non-specific

Low cost

Used for initial syphillis testing

73
Q

What tests are nontreponemal?

A

Venereal Disease Research Laboratory (VDRL)
Rapid Plasma Reagin (RPR)
Toludine Red Unheated Serum Test (TRUST)

74
Q

What is a negative Rapid plasma reagin test?

A

Carbon particles remain unclumped

75
Q

What is a positive Rapid plasma reagin test?

A

Clumped carbon from flocculation of the cardiolipin-based antigen by antibodies in the test serum

76
Q

What are Treponemal tests?

A

Detect antibodies directed against specific treponemal antigens and thus are more specific than non-treponemal tests

Qualitative only

Reported as reactive or nonreactive

More complex and more expensive

Only used as a confirmatory test for syphillis when non-treponemal tests are positive

77
Q

What are examples of treponemal tests?

A

Fluroescent treponemal antobody absorption (FTA-ABS)
Microhemagglutination test for anitbodies to T. pallidium (MHA-TP)
T. pallidium particle agglutination assay (TP-PA)
T. Palladium enzyme immunoassay (TP-EIA)

78
Q

What does the CDC now recommend for HIV testing?

A

Lab based 4th generation assays that detect HIV p24 antigen and HIV antibodies

If test is positive, a confirmatory HIV-1/HIV-2 antibody differentiation immunoassay must be performed

79
Q

What was the old way of testing for HIV?

A

ELISA and then Western Blot

80
Q

When should an HIV RNA test be done?

A

If the results of serologic studies are indeterminate of ir acute HIV infection is suspected

81
Q

What is the rapid HIV antibody test?

A

> 99% sensitive and specific

Perform on patient when healthcare worker is stuck with a needle they used on that patient

This test is only a preliminary test though and if it comes back positive it must be confirmed with a lab based combo antibody and antigen assay before a diagnosis of HIV can be made

82
Q

What does a urinary dipstick provide?

A

Rapid semi-quantitative assessment of urinary characteristics on a series of test pads embedded on a reagent strip

83
Q

What do dipsticks analyze urine for?

A 
Heme
Leukocyte esterase (WBCs)
Nitrite
Albumin (protein)
Ketones
pH
Specific gravity (concentration)
Glucose
84
Q

What should occur if heme is detected in urine?

A

A confirmation of blood via microscopy

85
Q

What may cause a false positive result for Leukocyte esterases in the urine?

A

Excessively dilute urine

86
Q

What may cause a false negative result for leukocyte esterases in the urine?

A

Concentrated urine
Proteinuria
Glucosuria

87
Q

What does nitrite presence in urine detect?

A

Infection

88
Q

What are the test options for Influenza testing?

A

1) rapid antigen tests
2) Immunofluorescence assays
3) Reverse transcriptase Polymerase chain reaction (RT-PCR)

All are relatively rapid

89
Q

What is the rapid antigen test for flu?

A

Sensitivity is awful

Immunoassays that detect influenza A and B nucleoprotein antigen in respiratory specimens

Qualitative results

15 minute results

FLu vaccine can cause a false positive

90
Q

What is the more reliable flu test?

A

Immunofluorescence antibody tests

91
Q

What is a direct or indirect immunofluorescence anitbody test?

A

Screening tests that yield result within hours

Can determine what type of flu it is: A vs. B

92
Q

What is a viral culture for flu testing?

A

Flu virus is cultured from nasal washes, throat swabs, sputum, or bronchoalveolar lavage specimens

Gold standard for lab diagnosis

Takes 48-72 hours

Used for confirming screening tests

93
Q

What do serologic tests for Lyme disease test for?

A

Antibodies to B. Burgdorferi

94
Q

What is the most commonly used initial serologic test to detect Lyme disease?

A

ELISA tests

95
Q

When can a false positive ELISA test be seen?

A 
Patients with:
Relapsing Fever
Syphillis 
Leptospirosis
Pinta
Yaws
Infective Endocarditis 
Viral illnesses
Autoimmune diseases = Systemic lupus erythematosus, or rheumatoid arthritis 
EBV
Malaria
96
Q

What does the acid fast bacilli staining test/Ziehl-Neelsen Stain used for?

A

Detects Mycobacterium Tuberculosis

Monitors disease state

Positive test retains stain and red boxcars of macrophages seen

97
Q

What is the technique for acid fast bacilli staining?

A

Fix sample in question
Stain with Fuchsin dye
Wash with an acid alcohol

98
Q

What cannot be made from a positive acid fast bacilli stain test?

A

A diagnosis of TB; positive stain needs to be followed up with confirmatory test

99
Q

What is the more specific and sensitive test for TB than a PPD?

A

Interferon Gamma Release Assay (IGRA)

100
Q

What are the advantages of IGRA?

A

Single patient visit
Results in 24 hours
Does not cause boosting effect from subsequent test
No false positives from prior BCG vaccine

101
Q

What are the disadvantages of IGRA?

A

Must be run within 8-30 hours of collection and sensitive to transport/testing conditions
Unknown if testing will have predictive power for TB disease
Limited data on children <5 y/o, recently exposed, immunocompromised, serial testing
Super expensive

102
Q

What do we use to detect malaria?

A

Thick and thin blood smears which are drawn on febrile patients

103
Q

What does a thick blood smear detect?

A

Thick, irregular amount of blood is dried and stained without fixing which increases the sensitivity of detection

Allows us to detect malaria

104
Q

What does a thin blood smear detect?

A

Thin smear is fixed to slide and stained

Parasitemia and speciation of malaria can be determined

105
Q

What does a lactate test detect?

A

Lactic acidosis which means patient is septic

106
Q

What concentration of lactate in the blood means that the patient has lactic acidosis?

A

> 4 meq/L

107
Q

What is responsible for the rise in lactate production in patients with sepsis?

A

Anaerobic metabolism is occuring

108
Q

What are the types of stool sample tests?

A

1) Fecal Leukocytes (WBCs) = suggestive of infammation
2) stool culture
3) Stool for Ova and parasites

109
Q

What is the stool culture positivity rate?

A

1.5-5.6%

110
Q

What does a routine stool culture detect and why?

A

Salmonella
Campylobacter
Shigella

Because these organisms are shed continuously so a negative result is typically truly negative

111
Q

What should you notify lab of testing stool for?

A

Yersinia
Aeromonas
Legionella

112
Q

What types of organisms are shed intermittently and require a stool O and P?

A

Giardia
Cryptosporidium
Cyclospora
Entamoeba histolytica

113
Q

What are possible indications that might require you to order a stool O and P?

A

Persistent diarrhea
Persistent diarrhea in the setting of foreign travel, particularly to mountainious areas
Persistent diarrhea with exposure to infants in daycare centers
Diarrhea in man who has had sex with men or a patient with AIDS
Community waterborne outbreak
Bloody diarrhea with few or no leukocytes

114
Q

What tests are used for C. diff testing?

A

Enzyme Immunoassay (EIA)
Polymerase Chain reaction (PCR)
Selective Anaerobic culture
Cell culture cytotoxicity assay

115
Q

What is the gold standard for C. diff detection?

A

Cell culture cytotoxicity assay

116
Q

What is the cell culture cytotoxicity assay?

A

Culture liquid stool on a layer of cultured fibroblasts and detection of morphologic rounding of the fibroblasts

Confirmation obtained by addition of antiserum with concomitant revesral of the effects

Takes 2 days to complete

117
Q

What is the more common test used for C. diff detection?

A

Initial EIA in acute setting

Tests for glutamate dehydrogenase antigen and toxins A/B

Results in 1 hour

118
Q

What is PCR used for in C. diff testing?

A

Initial test of confirmation of an EIA test

Results in 1 hour

Does not test for active production of toxin A/B

Sensitive

Does not distinguish between symptomatic and asymptomatic patients

ONLY use to test symptomatic patients

119
Q

What is the most sensitive test for C. diff?

A

Anaerobic cell culture

However, it can not distinguish between toxigenic and nontoxigenic strains

120
Q

What is important to remember with C. diff testing?

A

C. diff toxins degrade at room temp. and may be undetectable within 2 hours = FRESH IS BEST and keep it refrigerated

121
Q

What are is NAAT used to test for?

A

Chlamydia

Gonorrhea

122
Q

What specific NAAT is used to test for Chlamydia and Gonorrhea?

A

XPert CT/NG assay

results in 90 minutes

123
Q

What are culture methods limited use?

A

Research and reference labs only for chlamydia

124
Q

What can be considered a positive result for men with gonorrhea?

A

Gram stain demonstrating polymorphonuclear leukocytes with intracellular gram - diplococci

Diagnostic Methods (27 decks)

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