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
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
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)
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
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
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
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
8
Q
gram stain
A
- cell wall characteristics
- shape and arrangement allow for presumptive ID
- demonstrates cellular material and inflammatory response (WBC)
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
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
11
Q
bacterial meningitis in newborns
A
- e coli- GNR
- group B- GPC chains
- listeria GPR
12
Q
bacterial meningitis in children
A
- pneumococcus- GPC chains
- niesseria- GNDC
- H influenzae- pleomorphic GNR
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
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)
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
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
culture and recovery
- 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
initial differentiation based on growth characteristics
-initial colony observation allows for preliminary id based on size, topography, opacity, and different reactions based on agar
27
lactose fermenting GNR
-e coli,
kleb
citrobacter
enterobacter
28
non-lactose fermenting GNR
- proteus
- morganella
- salmonella
- shigella
- psuedomonas
29
viral culture
- tissue culture-need to grow human cells on plates for viruses
- some won't grow
30
film array
- multiplex PCR to detect many organisms
| - can detect what virus from one sample
