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CP > infection tests > Flashcards

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
Q

what occurs during and after preliminary resultd?

A

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
Q

what occurs in culture results?

A

the results of the tests are communicated to the clinician

27
Q

what happens in definitive results?

A

overnight incubation

identification using biochemical testing, additional susceptibility testing, identification by MALDI-TOF

28
Q

what is reported?

A

final summary for clinical care and communication

29
Q

what is gram stain?

A

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
Q

what will a positive gram stain show?

A

purple

31
Q

what will a gram negative stain show?

A

pink or the colour of the counter stain

32
Q

what does sensitivity testing require?

A

viable organisms - usually bacteria or fungi

liquid or solid media

33
Q

what is the basic principle of sensitivity testing?

A

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
Q

what is the role of sensitivity testing?

A

to inform decisions on targeted antimicrobial therapy so that you can start with empiric and then work towards targeted therapy in subsequent treatments

35
Q

what does sensitivity testing require?

A

isolation of the microorganism and antimicrobial susceptibility testing

36
Q

what are the uses of sensitivity testing?

A

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
Q

what are the limitations if sensitivity testing?

A

cultivable organisms only, is usually slower than direct testing and the correlation between antimicrobial sensitivity and clinical response is not absolute

38
Q

what is direct detection?

A

it is detection of the whole organism using microscopy or detection of a component of the organism using an antigen or nucleic acid

39
Q

what is an example of an antigen detection?

A

legionella antigen detection test

40
Q

what are the issues with antigen detection tests?

A

although they can be done at bedside and give quick results they require training to do and quality control can be an issue

41
Q

what types of antigens and give an example can be targeted?

A

polysaccharide capsules such as in neoformans, cell wall polysaccharides such as in aspergillus

42
Q

what is a limitation of the antigen test itself?

A

the solubility and distribution of an antigen will differ with different infecting species and this is poorly understood for aspergillus and candida

43
Q

what are used in serological tests?

A

latex agglutination in neoformans and ELISA in candida and aspergillus

44
Q

what is considered in the sampling protocol?

A

whether it should be screening or diagnostic, whether the diagnosis influences clinical outcome and whether the result offer any advantage over other methods

45
Q

what viruses, bacteria and fungi can be detected through nucleic acid detection?

A

virus - influenza
bacteria - strep pneumoniae
fungi - candida and aspergillus using 16S PCR

46
Q

what are the benefits of direct detection?

A

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
Q

what are limitations of direct detection?

A

it does not give any information on antimicrobial susceptibility and testing is usually the fastest diagnostic method

48
Q

what are immunological tests?

A

the detection of the immune response to infection - IgM or ABs, or using seroconversion

49
Q

what is seroconversion?

A

seroconversion is the time period during which a specific antibody develops and becomes detectable in the blood

50
Q

what will happen over seroconversion?

A

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
Q

what is titre?

A

it is the greatest dilution at which antibody is detectable

52
Q

what is an example of an immunological test?

A

IFN-y release assays in TB

53
Q

what are the uses of antibody testing?

A

confirms the exposure to a specific microorganism and can be cultivable and non cultivable organisms

54
Q

what are the limitations of antibody testing?

A

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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