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infection tests Flashcards

1
Q

what are infection tests for?

A

optimal treatment and prevention of infection

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2
Q

why would you carry out a diagnostic test?

A

to improve outcome or to provide epidemiological data

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3
Q

how is a diagnostic hypothesis reached?

A

through history, examination, non - microbiological tests, lab tests

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4
Q

what is direct detection?

A

it is detection of a whole organism, antigen or genomic material

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5
Q

what does serology detect?

A

an antibody response

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6
Q

what is fever a sign of?

A

a sign of inflammation and can be a sign of infection

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7
Q

what is the most common cause of community acquired pneumonia?

A

streptococcus pneumoniae

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8
Q

`how is Hb related to infection?

A

can be anaemia of chronic disease - normocytic or chromic caused by infection

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9
Q

what is the use of WCC?

A

can be raised in infection and other condition and therefore is not specific. Severe sepsis can lower WCC

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10
Q

what are the levels of markers in bacterial infection?

A

WCC raised, lymphocytes are normal or low, neutrophils are raised

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11
Q

what are the levels of markers in viral infection?

A

normal WCC, raised lymphocytes and normal neutrophils

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12
Q

what are the inflammatory markers of the innate immune system?

A

procalcitonin (0.5micrograms/L) and CRP (<0.5mg/L) - raised means diagnosis of infection

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13
Q

what imaging is used to support a diagnosis of respiratory infection?

A

chest Xray, CT and CT combined with PET

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14
Q

what two tests can help to identify severe sepsis and respiratory failure?

A

blood gases and blood lactate

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15
Q

what comprises biological diganosis?

A

culture, direct detection and immunological tests

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16
Q

what needs to be done for ABs are started?

A

culture

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17
Q

what can culture do?

A

it enables the identification of organisms by immediate or further testing, typing to establish organism relatedness and sensitivity testing to direct antimicrobial therapy

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18
Q

what is culture?

A

it is the isolation of viable pathogens

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19
Q

what is the process of sampling?

A

patient sampling, sampling handling, sampling transport incubation, growth detection , preliminary results, incubation, culture results, definitive results and then reporting

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20
Q

what is considered in patient sampling?

A

the aseptic technique to reduce contamination and the optimal volume for sensitivity

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21
Q

what will local sample handling guidelines tell you?

A

the safety, labelling, number of samples and bottles required

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22
Q

when should the samples be transported to the lab?

A

as soon as possible

23
Q

what happens in the incubation stage?

A

incubate at 35-37 degrees for 5-7 days and detect microbial growth through the constant automatic monitoring of CO2 - if no growth then the specimen is negative and discarded

24
Q

what is used in growth detection?

A

TTP - time to positivity
TTP is usually 12-24 hours for significant bacteriaemia
shorter if overwhelming sepsis
longer if more fastidious organism

25
what occurs during and after preliminary resultd?
in preliminary a gram stain is observed and then incubation means that the pathogen is incubated on a range of culture media for susceptibility testing to guide antimicrobial therapy
26
what occurs in culture results?
the results of the tests are communicated to the clinician
27
what happens in definitive results?
overnight incubation | identification using biochemical testing, additional susceptibility testing, identification by MALDI-TOF
28
what is reported?
final summary for clinical care and communication
29
what is gram stain?
it is a chemical process that distinguishes between the bacterial cell walls that retain crystal violet and those that do not when stained and washed with acetone
30
what will a positive gram stain show?
purple
31
what will a gram negative stain show?
pink or the colour of the counter stain
32
what does sensitivity testing require?
viable organisms - usually bacteria or fungi | liquid or solid media
33
what is the basic principle of sensitivity testing?
it is the culture of a microorganism in the presence of an antimicrobial agent to work out if the concentration of the antimicrobial will be high enough in the body to kill the micro-organism
34
what is the role of sensitivity testing?
to inform decisions on targeted antimicrobial therapy so that you can start with empiric and then work towards targeted therapy in subsequent treatments
35
what does sensitivity testing require?
isolation of the microorganism and antimicrobial susceptibility testing
36
what are the uses of sensitivity testing?
establishes the presence of a microorganism at a particular site, provides epidemiological data and typing information and allows the use of empiric and targeted therapy
37
what are the limitations if sensitivity testing?
cultivable organisms only, is usually slower than direct testing and the correlation between antimicrobial sensitivity and clinical response is not absolute
38
what is direct detection?
it is detection of the whole organism using microscopy or detection of a component of the organism using an antigen or nucleic acid
39
what is an example of an antigen detection?
legionella antigen detection test
40
what are the issues with antigen detection tests?
although they can be done at bedside and give quick results they require training to do and quality control can be an issue
41
what types of antigens and give an example can be targeted?
polysaccharide capsules such as in neoformans, cell wall polysaccharides such as in aspergillus
42
what is a limitation of the antigen test itself?
the solubility and distribution of an antigen will differ with different infecting species and this is poorly understood for aspergillus and candida
43
what are used in serological tests?
latex agglutination in neoformans and ELISA in candida and aspergillus
44
what is considered in the sampling protocol?
whether it should be screening or diagnostic, whether the diagnosis influences clinical outcome and whether the result offer any advantage over other methods
45
what viruses, bacteria and fungi can be detected through nucleic acid detection?
virus - influenza bacteria - strep pneumoniae fungi - candida and aspergillus using 16S PCR
46
what are the benefits of direct detection?
it establishes the presence of an organism at a particular site, can be cultivable and non cultivable organisms and allows the use of the appropriate empiric theory
47
what are limitations of direct detection?
it does not give any information on antimicrobial susceptibility and testing is usually the fastest diagnostic method
48
what are immunological tests?
the detection of the immune response to infection - IgM or ABs, or using seroconversion
49
what is seroconversion?
seroconversion is the time period during which a specific antibody develops and becomes detectable in the blood
50
what will happen over seroconversion?
there will be a change from a negative to a positive result in subsequent tests, a four fold rise in titre - a rise in the concentration of AB from one test to following
51
what is titre?
it is the greatest dilution at which antibody is detectable
52
what is an example of an immunological test?
IFN-y release assays in TB
53
what are the uses of antibody testing?
confirms the exposure to a specific microorganism and can be cultivable and non cultivable organisms
54
what are the limitations of antibody testing?
it is restricted to patients with a detectable antibody response and is retrospective and therefore may be too late to inform the antimicrobial therapy decisions

CP (38 decks)

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