Diagnosis of an Infection

Question 1

What general symptoms are seen with infections?

Answer 1

• Pyrexia
• General malaise
• Rash
• Headache, abdominal, or respiratory symptoms
• Septic shock

Question 2

What may the pattern of pyrexia be specific to?

Answer 2

Different infective causes

Question 3

What conditions, other than infections, can cause pyrexia?

Answer 3

• Malignancy
• Drugs
• Other diseases

Question 4

What is meant by general malaise?

Answer 4

Flu-like symptoms

Question 5

What does general malaise result from?

Answer 5

Cytokines

Question 6

When is septic shock produced?

Answer 6

Severe infection

Question 7

What may the site of the actual infection show?

Answer 7

• Local pain
• Discharge
• Coughs
• Sputum production
• Diarrhoea

Question 8

How can infectious agents be categorised?

Answer 8

• Toxin mediated
• Acute pyogenic
• Sub-acute
• Chronic granulomatous

Question 9

What is it important to consider when looking at infection to give a better understanding of the disease?

Answer 9

The exposure to the likely source

Question 10

What are the categories potential exposures to the source?

Answer 10

• Endogenous
• Exogenous

Question 11

What should be do when it is suspected an individual has an infection?

Answer 11

• History taken
• Clinical examination
• Samples for microbiological testing

Question 12

What is the purpose of the history and clinical exam when an individual is suspected to have an infection?

Answer 12

So a differential diagnosis can be produced

Question 13

What types of specimen can be taken for microbiological investigation?

Answer 13

• Blood
• Pus
• Lavage

Question 14

What should happen once a specimen has been taken?

Answer 14

It should be cultured

Question 15

Why should a specimen be cultured when taken for clinical examination?

Answer 15

To increase the number of microbes grown for identification

Question 16

What can cultures be used to do?

Answer 16

Limit the growth of certain pathogens to reduce any contaminants in the sample

Question 17

How may a clinical sample for investigation get contaminated?

Answer 17

Poor aseptic technique obtaining the sample

Question 18

What potential problem could arise when trying to culture a sample for microbiological investigation of an infection?

Answer 18

Many organisms are obligate anaerobes, which will be killed in exposure to an atmosphere with oxygen

Question 19

What is required for viruses to grow?

Answer 19

A cell culture

Question 20

What should happen following the obtaining of a clinical specimen?

Answer 20

The sample must be analysed

Question 21

What are the categories of mechanisms for analysing a clinical specimen?

Answer 21

• Microscopy
• Molecular techniques
• Serology

Question 22

How can the sample be analysed microscopically?

Answer 22

Via various staning or flouresence

Question 23

What stain is used for bacteria?

Answer 23

A gram stain

Question 24

For what bacteria can a gram stain not be used?

Answer 24

Mycobacterium

Question 25

What stain is require to examine mycobacterium microscopically?

Answer 25

ZN stain

Question 26

What samples can be examined microscopically directly *(with no stain)*?

Answer 26

Stool samples

Question 27

What can be indentified when examining a stool sample directly?

Answer 27

Parasites

Question 28

What can be used for viral detection?

Answer 28

Electron microscopy

Question 29

What can be used to diagnose RSV?

Answer 29

Flouresence

Question 30

What is the main molecular technique used in microbiological examination?

Answer 30

Nucleic acid amplification testing (NAAT)

Question 31

What is NAAT used to identify?

Answer 31

Both bacteria and viruses

Question 32

How does NAAT work?

Answer 32

It amplifies target DNA or RNA, until sufficient quantities have been cultured, and machines can then test the nucleic acid and identify the species

Question 33

What is NAAT very useful for?

Answer 33

Organisms that are slow growing or dangerous to grow

Question 34

What is serology?

Answer 34

Testing for the blood serum for an immune response against a specific pathogen

Question 35

How is a diagnosis made using serology?

Answer 35

By detecting a rise in antibody levels, or the presence of an IgM antibody

Question 36

What techniques of serology are used?

Answer 36

* Agglutination * Enzyme immunoassay * Complement fixation

Question 37

What does agglutination involve?

Answer 37

The clumping together of antibodies to produce a large group, *which can then be identified to identify the bacteria involved*

Question 38

What happens in enzyme immunoassay?

Answer 38

Antibodies specific for the IgG antibodies for certain reactions are on a solid support, and will produce a response if they bind to the specific IgG antibody for the certain microbe

Question 39

What are antibody levels often quoted as?

Answer 39

Titres

Question 40

What are titres?

Answer 40

The reciprocal of the last dilution at which Ag-Ab complex could be detected

Question 41

What should be done if the laboratory findings do not match the clinical findings?

Answer 41

The laboratory results should be questioned for a potential false positive

Question 42

What is it important is done for the final diagnosis?

Answer 42

The microbiology is matched to the clinical findings

Question 43

What can be done following identification for some bacteria and fungi?

Answer 43

Check the antibiotic susceptibility

Question 44

How can bacteria be classified? ## Footnote *With regards to antibiotic susceptibility*

Answer 44

* Susceptible * Moderately resistant * Resistant

Question 45

What is meant by a susceptible bcateria?

Answer 45

One where a normal dose of antibiotic results in cure

Question 46

What is meant by a moderately resistant antibiotic?

Answer 46

One where a large dose of antibiotic results in cure

Question 47

What is meant by resistant antibiotic?

Answer 47

One where antibiotics are likely to fail

Question 48

What is the main technique for determining antibiotic susceptibility?

Answer 48

Grow the culture in medium, and placing antibiotic impregnanted disks into the medium and measuring the diameter on inhibition on the plate

Question 49

What does testing for antibiotic susceptibility provide?

Answer 49

An estimate into how well the patient will react to therapy

Question 50

What is the limitation of testing for antibiotic susceptibilty?

Answer 50

The clinical response will also depend on host factors

Question 51

Other than using discs, how can antibiotic susceptibility be checked?

Answer 51

Using broth dilution tests

Question 52

What do broth dilution tests provide?

Answer 52

* A minimum inhibitory concentration (MIC) * A minimum bactericidal concentration (MBC)

Question 53

What is the minimum inhibitory concentration?

Answer 53

The minimum concentration of antibiotic that can be given to inhibit growth

Question 54

What is the minimum bactericidal concentration?

Answer 54

The minimum concentration of an antibiotic that can be given to kill the bacteria

Question 55

Label this picture of a broth dilution test

Answer 55

* A - Minimum Inhibitory Concentration * B - Minimum Bactericidal Concentration * C - Growth on subculture

Question 56

What are the advantages of culture dependant identification?

Answer 56

* Can test other properties * Sensitive and specific

Question 57

What other properties can be tested for using culture dependant identification?

Answer 57

* Sensitivity * Virulence * Phenotype

Question 58

What are the disadvantages of culture dependant identification?

Answer 58

* Slow * Organism must be alive * Low yield post-antibody response * Method often highly organism specific

Question 59

What are the advantages of culture independant identification?

Answer 59

* Rapid * Organism can be alive or dead * Suitable after antibody response * Sensitive

Question 60

What are the disadvantages of culture indepedant identification?

Answer 60

* Limited testing of other properties * Potential for contamination * Same methods apply to all organisms