Making an Infection Diagnosis Flashcards

1
Q

What does microbiology do ?

A

Identify the infecting organism

Susceptibility testing

Identify clustered organisms over-represented in the community.

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2
Q

Diagnostic advice

A

Identify the infecting organism

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3
Q

Treatment advice

A

Susceptibility testing

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4
Q

Infection control

A

Identify clustered organisms over-represented in the community.

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5
Q

What are laboratory results for ?

A
  • Act as a doctors back up
  • Alert us to patients where the clinicians suspect infection but have not bothered to contact
  • Help out when antibiotics are unpredictable
  • Permit collection of alert organisms and detection of outbreak samples
  • Provide an intelligence system
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6
Q

Why don’t clinicians use microbiology results ?

A

The speed of progression of infection is much
faster than the time taken to generate results
(we are too slow)

They do not understand the implications of
the data.

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7
Q

Describe some roles of clinical microbiologist

A

To provide :

  • high quality diagnostic tests
  • a clinical consultation service for patients with suspected infection
  • clinical advice on the interpretation of diagnostic tests
  • advice on therapy of serious infections
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8
Q

Describe the process of a diagnosis

A

Patient doctor interaction
Differential diagnosis
Clinical specimens
Results - refinement of differential diagnosis
Diagnosis
Therapy

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9
Q

How to make a microbiological diagnosis ?

A

Direct examination
Culture
Serology
Molecular

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10
Q

What is serology ?

A

To check for the presence or level of specific antibodies in the blood.

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11
Q

Types of Microscopy

A

Light
Fluorescent
Electron microscopy

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12
Q

Types of light microscopy

A

Direct
Gram
Z-N
Giemsa

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13
Q

Direct light microscopy

A

stool - parastites

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14
Q

Gram light microscopy

A

CSF - bacteria

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15
Q

Z-N light microscopy

A

sputum - TB

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16
Q

Giesma light microscopy

A

blood - malaria

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17
Q

What is fluorescence microscopy used for ?

A

Respiratory syncytial virus
RSV diagnosis

18
Q

What is electron microscopy used for ?

A

Virus detection and identification

19
Q

Culture diagnosis features

A
  • More sensitive than smear
  • Allows susceptibility testing
  • Allows rapid presumptive diagnosis
  • Allows detailed identification
  • Rendered negative by antibiotics
20
Q

Smear diagnosis description

A
  • Rapid
  • Simple to perform
  • Cheap
  • Not very sensitive
    *Not very specific
  • Requires considerable expertise
21
Q

MALDI-TOF description

A

A positive step

  • Rapid identification of bacteria
  • Does not provide susceptibilities
  • Delayed by slow growth
  • Of no value if antibiotics render cultures negative
22
Q

Serological diagnosis function

A
  • Detect high IgG concentration
  • Detect rising of falling titres
  • Detect IgM/IgA
  • Measure avidity of binding
  • Detect antigen
23
Q

Name 7 examples of serological techniques

A

Agglutination
Precipitation
Complement fixation
Virus neutralisation
ELISA
Radioimmunoassay
Immunofluorescence

24
Q

Examples of molecular techniques

A

DNA hybridisation.
Nucleic acid amplification testing.
- PCR
- LCR
- Automated DNA amplification
- Real time PCR

25
Q

Culture based diagnosis

A
  • Detect high IgG concentration
  • Detect rising of falling titres
  • Detect IgM/IgA
  • Measure avidity of binding
  • Detect antigen
26
Q

Examples of specimens

A

UTI - midstream urine
Wound - pus or swab
Meningitis - CSF and blood
Pyrexia of unknown origin - serology
Pneumonia - sputum, lavage, serology

27
Q

How to test for specimens with a single pathogen ?

A
  • Throat swab (except diphtheria suspected)
  • Infection control screening
  • Unusual infections e.g., pertussis
  • Mtb detection
28
Q

How to test for specimens where a few organisms are likely ?

A

CSF
STI samples
Blood

29
Q

How to test for specimens with multiple pathogens ?

A
  • Faeces
  • Abscess pus
  • LRTI samples
  • Oral swab
  • (Urine)
30
Q

How to interpret clinical tests ?

A
  • Test sensitivity and specificity
  • Impact of normal flora on
  • The fourth dimension- do I need a test – can I
    get a test?
31
Q

What is test sensitivity ?

A
  • The ability of a test to detect all of the true positives
  • Equal to the number of positives obtained divided by the total number of positives
32
Q

What is test specificity ?

A
  • Ability to identify the number of true negatives
  • Equal to the number of negatives obtained divided by the number of true negatives
33
Q

Normal flora

A
  • Its everywhere
  • Many of the pathogens are also colonisers
  • Interpretation of all microbiology results must be made in the context of the normal flora
34
Q

Normal flora in nasopharynx

A

Streptococci
Haemophilius
Neisseria
Mixed anaerobes
Candida
Actinomyces

35
Q

Normal flora in skin

A

Staphylococci
Streptococci
Corynebacteria
Proprionibacteria
Yeasts

36
Q

Normal flora in upper bowel

A

Enterobacteriaceae
Enterococci
Candida

37
Q

Normal flora in lower bowel

A

Bactericides
Bifidobacteria
Clostridium
Peptostreptococci

38
Q

Normal flora in vagina

A

Streptococci
Lactobacilli
Corynebacteria
Candida
Actinomyces
Mycoplasma hominid

39
Q

What are the cultures like for patients with a viral infection ?

A

Negative cultures

40
Q

Drawbacks of legionella

A

Grows slowly and requires specialist medium

41
Q

Drawbacks of mycoplasma pneumoniae

A

Requires specialist medium and 14 days to grow

42
Q

Drawbacks of chlamydia psittaci
chlamydophyla pneumoiae

A

Obligate intracellular pathogen