SM 182 Testing Flashcards by Ashwin Sunderraj

Why have vaccines against Strep pneumo and H. flu type B improved outcomes?

Vaccines help reduce systemic infections

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What type of pathogen tends to cause respiratory infections?

Respiratory infections tend to be viral

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What is the role of Hemaglutinin in Influenza?

HA mediates entry into host cells

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What is the role of Neuraminidase in Influenza?

NA mediates exit from host cells

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What type of virus is RSV and who does it tend to infect?

RSV is an RNA virus that tends to cause bronchiolitis and pneumonia in children

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Is there a vaccine for RSV?

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What is the prophylactic treatment for RSV?

Palvizumab

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When and how does RSV spread?

RSV is seasonal and spreads via secretions

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What type of virus is Adenovirus?

Nonenveloped dsDNA virus, found all throughout the body

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Why might a positive result for an Adenovirus test be misleading?

Adenovirus is found all over the body, and may not actually be responsible for a disease; need a clinical picture to diagnose Adenovirus infection

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Why is it hard to test for Adenovirus?

There are several serotypes of Adenovirus, which makes it difficult to detect all of them in a single assay

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Is adenovirus seasonal?

No, Adenovirus and Coronoavirus are year round

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Why might NAAT’s not be effective against certain strains of coronavirus?

MERS and SARS and nCOV are not detected because they are too new

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What are the benefits of tests that rapidly detect respiratory viruses?

Reduce antibiotic use, optimize antiviral therapy, infection control and better use of radiographs

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When should specimens be collected for analysis and laboratory diagnosis?

As early as possible, typically via nasopharyngeal samples

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What method cannot be used for clinical diagnosis of a virus?

Serology/Antibodies cannot be used to dx a viral infection, ever

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What methods can be used for clinical diagnosis of a virus?

Molecular methods (ideal), rapid antigen detection, and virus culture

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Why is virus culture no longer the gold standard for virus diagnostic testing?

Virus culture is no longer recommended because it takes too long to grow the culture

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How can viral culture show virus presence?

Although culture is no longer used to dx viral infection, the culture could show fusion of the culture cells or be stained with a fluorescent antibody

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What are the test characteristics of rapid antigen detection?

Fast, but less sensitive than NAAT

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What does rapid antigen detection work?

RAT detects the antigen-antibody complex

What are the pros and cons of RAT?

RAT like immunoassays are easy to use, point of care, cheap, and rapid, but have limited sensitivity/assay performance

What are the pros of molecular assays?

Molecular assays like PCR are fast, high sensitivity, and high specificity

How does automation help molecular assays?

Allows for simplification of testing process and lowering turnaround time, as well as detection of multiple targets, allowing for detection of multiple targets at the same time

Can automated molecular tests detect bacteria or viruses?

Automated molecular tests like the FilmArray respiratory panel detect viral and bacterial pathogens simultaneously

What are the limitations of multiplex assays?

Assay performance (reduced sensitivity for viruses with many serotypes) and increased costs

Who are multiplex assays best used on?

Seriously infected patients in an inpatient setting that requires intensive care

What is a limitation of molecular point of care assays?

Although very rapid, these assays are prone to contamination due to operator error

Which form of viral detection assay has the lowest sensitivity?

Rapid antigen testing via methods like lateral flow have low sensitivity

Describe the pathogenesis of TB?

Macrophages express TB antigen on MHCII and release IL-12 to activate TB-specific Th1 cells, which in turn release IFN-Gamma to activate Macrophages

What two cell types maintain control of TB?

Macrophages and Th1 cells

What two signaling molecules form a loop that control TB?

IL-12 released by Macrophages and IFN-Gamma released by Th1, which allow for granulomatous control of TB

Deficiencies in what proteins can result in the loss of control over TB infection?

Deficiencies in IL-12 and IFN-Gamma Receptor proteins result in a loss of control over TB as the Granulomatous loop cannot be maintained

Repeated mycobacterium infections point to what defect?

Defects in IFN-GammaR or IL-12R

How can STAT1 phosphorylation be used as a readout of sensitivity to TB infection?

After IFN-Gamma binds to its receptor on Macrophages, STAT1 dimerizes and is phosphorylated in B-cells; healthy px show increasing STAT1 phosphorylation with increasing IFN-Gamma, while px with defective IFN-GammaR do not show an increase in STAT1 phosphorylation with increasing IFN-Gamma

Is STAT1 loss of function determined by one allele?

No; heterozygotes with mutations in 2 loci can result in loss of function of the IFN-GammaR

How is the BCG vaccine administered and what can greatly reduce its immunogenic potential?

BCG vaccine is administered as a single shot using live attenuated M. bovis, but loses 99% of viability if exposed to the sun

What is in the BCG vaccine?

Live attenuated M. bovis

What are potential complications of the BCG vaccine?

Accelerated reactions to the vaccine occur if the px was previously exposed to TB, and infection may disseminate in an immunocompromised host

Is the BCG vaccine recommended in the US?

No, due to low prevalence of TB < 1%

Is the BCG vaccine effective at preventing TB?

BCG vaccine can prevent systemic infection of TB, but does not prevent pulmonary disease from TB exposure

How does the PPD skin test work?

Intradermal administration of non-species specific molecules to induce the formation of a nodule

Which species is the PPD skin test using?

The PPD skin test is not species specific

What can cause a false positive on the PPD?

Exposure to NTM like MAC can cause a positive test result on the PPD

How is a PPD test read?

Measure the diameter of the nodule, not the erythema, and compare to cutoff

What are disadvantages tot he PPD skin test?

False+ BCG vaccines and repeated testing, false+ with previous NTM exposure, return visit to physicians office required, and inaccuracies with measurement common

Does the Quantiferon TB test remove false positives?

Uses peptides not found in the BCG vaccine but may still be found in environmental mycobacteria, so removes some but not all false positives

How does the Quantiferon TB test work?

Uses 4 tubes with 1mL blood; neg control, pos control, and CD4 T cell as well as CD8 T cell responses

How does the T-spot test work for TB?

Separate PBMC's from whole blood, and expose peptides not from the BCG (but still may be found in NTM) to cells, and measure spots formed from antibody precipitation = Spot Forming Cells (SFC)

What is the gold standard for diagnosing latent TB infection?

There isn't one

Can radiology be used to distinguish between active and latent TB?

Nope, and neither can the TST or IGRA; need a clinical picture

What is one advantage of the Quantiferon over the T-spot?

It is unaffected by subjective interpretation of results, like the spot size on the T-spot, and does not require the patient to return to the office