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Micro/Immuno Part 2 > Diagnosis of Infectious Disease > Flashcards

Diagnosis of Infectious Disease Flashcards

1
Q

clinician needs to know

A
  • labs test menu
  • specimen collection and transport guidelines
  • testing policies
  • appropriate specimens and tests
  • how to prioritize
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2
Q

diagnosis of infectious disease

A
  • clinical syndromes are rarely specific for single pathogens
  • having an understanding of the organisms most frequently associated with a clinical presentation allows for empiric therapy until definitive lab results are available
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3
Q

fiver general approaches for diagnosis

A
  • microscopy
  • culture
  • detection of bacterial antigens
  • demonstration of specific nucleic acids (molecular techniques)
  • detection of antibodies directed against the organism (serology)
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4
Q

typical turnaround times using conventional clinical microbiology techniques

A
  • day 1-specimen processing, plating and staining
  • day 2- culture exam, identification and sensitivity setup
  • day 3- id and sensitivity tests read
  • day 4 physician review of culture results
  • certain organisms take longer to grow and therefore culture results may take longer
  • fastidious-2-4 weeks
  • fungi-4-6 weeks
  • TB up to 8
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5
Q

garbage in garbage out

A
  • proper collection and transport is critical to the quality of results produced by the lab
  • validity of all diagnostic information produced in the lab is contingent on the quality of the specimen received
  • consequences of poorly collected and/or poorly transported specimens include failure to isolate the causative org, and recovery of contaminants or normal flora, which could lead to improper treatment of the patient
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6
Q

fundamentals of collection

A
  • collect specimen in acute phase of infection-before antibiotics
  • select correct anatomic site
  • use proper technique-minimal contamination
  • collect appropriate quality
  • pack to maintain viability and prevent leakage
  • label specimen accurately
  • transport or store specimen promptly
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7
Q

various stains and prep

A
  • confirm submitted material is representative
  • identify cellular components and debris of inflammation to estimate the probability of infection
  • identify specific infectious agents
  • guide physicians to early treatment with antibiotics
  • support or refute initial physician idiagnosis
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8
Q

gram stain

A
  • cell wall characteristics
  • shape and arrangement allow for presumptive ID
  • demonstrates cellular material and inflammatory response (WBC)
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9
Q

impetigo

A
  • s aureus or s pyogenes
  • organism gram reaction and morphology provides possible cause allowing for selection of empiric therapy
  • the presence of inflammatory cells is also indicated
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10
Q

common things happen commonly

A

-knowledge of the most frequent agents associated with specific infections and their gram reaction and morphology can allow for presumptive id before culture or other test results are available

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11
Q

bacterial meningitis in newborns

A
  • e coli- GNR
  • group B- GPC chains
  • listeria GPR
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12
Q

bacterial meningitis in children

A
  • pneumococcus- GPC chains
  • niesseria- GNDC
  • H influenzae- pleomorphic GNR
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13
Q

detection of bacterial antigens

A
  • variety of immunoassays are available for the detection of bacterial antigens directly from clinical material
  • generally 100% specific but not 100% sensitive
  • decreased sensitivity may be due to improper specimen collection and transport, inappropriate timing of collection, or assay format
  • in some cases, antigen detection is the method of choice-legionella in urine
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14
Q

antigen detection formats

A
  • latex agglutination-antibody coated onto latex particle, when a sample contains the antigen it causes visible agglutination of the particles
  • coagglutination-antibodies are bound to bacteria, wen sample contains antigen it causes visible agglutination of the bacteria
  • direct fluorescent antibody-antibodies tagged with fluorescent dye
  • ELISA
  • Immunochromatographic assays- sample mobilizes gold particles coated with monoclonal antibodies. if antigen is present in the sample, a complex is formed between the capture antibody and the monoclonal antibody gold conjugate, which can be seen (gold+monoclonal binds to capture antibody and antigen)
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15
Q

Rapid diagnosis of group A strep

A
  • a number of assays are available that allow for the detection of S pyrogenes directly from a swab of the tonsillar area
  • not 100% sensitive 100% specific
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16
Q

serological diagnosis

A
  • not all infectious agents have available antigen assays or culture techniques
  • determines disease susceptibility or immunity
  • diagnose a current or previous infection
  • Ad-specimen easy to get, tests widely available, ease of specimen transport
  • Disad-IgG requires acute and convalescent sera in some diseases, IgM can have false pos and false neg, 2-3 week delay in diagnosis in infections with short incubation period
17
Q

IgM after infection

A
  • appears in serum in 1-2 weeks
  • persists for 2-3 months
  • consistent with current or recent infection
18
Q

IgG after infection

A
  • appears 2-3 weeks after infection
  • may persist for life
  • may represent somewhat recent infection or immunity
19
Q

antibody titers

A
  • amount of antibody at a particular dilution of patient serum
  • 1:2, 1:4 etc
  • higher dilution is consistent with higher level of antibody in patient serum
20
Q

acute and convalescent antibody titers

A
  • asses IgG at 2 phases
  • simultaneous assay of both sera is most meaningful
  • acute phase-first serum sample collected after exposure or symptom onset, may be asymptomatic
  • convalescent phase-serum sample collected 2-4 weeks later
  • compare acute and convalescent results-4 fold rise in titer of paired sera collected 204 weeks apart verifies recent infection and is diagostically significant
21
Q

molecular approaches

A
  • nucleic acid based tests for nucleic acid amplification tests are increasingly used for detection and id of microorganisms and viruses directly from clinical specimens, id from culture material
  • only a few FDA approved
22
Q

why use molecular test

A
  • allows for detection and id of causative agents that are:
  • difficult to culture-metapneumovirus
  • fastidious-pertussis
  • slow growing
  • highly infectious-brucella
  • increased sensitivity over current methods-flu A and c diff
  • detect carrier/colonization-MRSA
  • detection of resistance
23
Q

HSE

A
  • herpes simplex encephalitis
  • most common cause of sporadic, fatal encephalitis
  • infection of brain parenchyma, esp temporal and frontal lobes-hemorrhage and necrosis
  • occurs as a complication of primary infection in the neonate-HSV2
  • reactivation of latent disease in older children and adults-HSV1
  • clinical presentation and imaging are sensitive but not specific
  • mortality is >70% if untreated
  • Upstate has RT-PCR for detection and uses FRET probe and melt curve analysis to distinguish strains for treatment
  • could also do DFA or culture
24
Q

limitations of nucleic acid amplification tests

A
  • relatively expensive-reagents, equipment, space
  • availability-few FDA cleared assays
  • still need for organism isolation/AST
  • detect both live and dead organisms
  • risk of contamination and false pos
  • not 100% sensitive or specific
25
Q

culture and recovery

A
  • traditional method
  • organisms have specific nutritional and growth requirements
  • clinical labs use a variety of media to enhance the recover
  • cannot culture for all organisms all the time- need to ask for things that aren’t routine
26
Q

initial differentiation based on growth characteristics

A

-initial colony observation allows for preliminary id based on size, topography, opacity, and different reactions based on agar

27
Q

lactose fermenting GNR

A

-e coli,
kleb
citrobacter
enterobacter

28
Q

non-lactose fermenting GNR

A
  • proteus
  • morganella
  • salmonella
  • shigella
  • psuedomonas
29
Q

viral culture

A
  • tissue culture-need to grow human cells on plates for viruses
  • some won’t grow
30
Q

film array

A
  • multiplex PCR to detect many organisms

- can detect what virus from one sample

Micro/Immuno Part 2 (17 decks)

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