Micro_Rapid Diagnostics Flashcards
Outcomes of studies of rapid diagnostics
A meta-analysis found that for patients with bloodstream infections, only rapid diagnostic tech- niques, together with direct communication to a member of the antimicrobial stewardship team, led to significant differences in the time to optimal therapy.
molecular rapid diagnostic testing, including tests such as PCR, MALDI-TOF MS, and peptide nucleic acid fluorescent in situ hybridization (PNA FISH), was associated with significant decreases in mortality risk in the presence of active review of results by an antimicrobial steward- ship team, but not in its absence
T2 MR technique
Performed on whole blood when magnetic particles are coated with agents specific for binding
to the pathogen of interest. When the pathogen is detected, the DNA binds and clusters, causing
microscopic disruptions in the magnetic fields.
b. Currently FDA approved for five pathogenic Candida spp.: C. albicans, C. tropicalis, C. parapsi-
losis, C. krusei, and C. glabrata
Accelerate Pheno system characteristics
Accelerate Pheno system (Accelerate Diagnostics, Tucson, AZ) is a fully automated test system that performs both identification and AST through (1) lysis of red blood cells and separation of blood com- ponents, (2) gel electrofiltration, (3) immobilization, (4) identification by FISH, and (5) AST through time-lapse imaging. a. Performed directly from positive blood cultures within around 7 hours i. Time to identification: 1½ hours ii. Time to antibiotic susceptibilities: Around 7 hours
Lacks clinical evidence
Time to positivity
one from the catheter or port and one from peripheral venipuncture, processed in a continuous-monitoring BC sys- tem. If both BCs grow the same organism and the BC drawn from the device becomes positive >2 hours before the BC drawn by venipuncture, there is a high probability of cathe- ter-associated BSI
Most important determinants of blood culture positivity
adults, 20–30mL of blood per culture set (depending on the manufacturer of the instrument) is recommended and may require >2 culture bottles depending on the system
second important determinant is the number of blood culture sets performed during a given septic episode
Most common cause of viral encephalitis
The California Encephalitis Project identified a defi- nite or probable etiologic agent for only 16% of 1570 immuno- competent patients enrolled from 1998 to 2005 (69% viral, 20% bacterial, 7% prion, 3% parasitic, 1% fungal); a possible cause was identified for an additional 13% of patients
The virus most commonly iden- tified as causing encephalitis is herpes simplex virus (HSV) with 90% HSV-1. The sensitivity and specificity of NAAT for HSV encephalitis are >95%; early data showed that HSV is cultured from CSF in <5% of cases
Threshold quantiation for respiratory samples in pNA
The generally accepted thresholds are as follows: endotracheal aspirates, 106 colony-forming units (CFU)/mL; BAL fluid, 104 CFU/mL; protected specimen brush samples, 103 CFU/mL
Pathogens in peritoneal dialysis associated peritonitis
PDAP, however, the list of likely suspect organisms is quite different from SBP. Gram- positive bacteria (predominantly Staphylococcus spp and, to a lesser extent, Streptococcus and Corynebacterium spp) account for >60% of cultured microorganisms. Gram-negative bacteria (mostly E.coli, Klebsiella, and Enterobacter spp) represent <30% of positive cultures while anaerobes comprise <3% of isolates
Reverse testing for syphilis
Many high-vol- ume clinical laboratories have reversed the testing sequence and begin the testing algorithm first with a specific trepone- mal test, such as an EIA or chemiluminescence immunoassay, and then retesting reactive results with a nontreponemal test, such as RPR, to confirm diagnosis
Animal bite pathogens
2 most prominent groups of microorganisms initially considered in the evaluation of patients are Pasteurella spp, namely P.canis (dogs) and P. multocida subsp multocida and subsp septica (cats) or Capnocytophaga canimorsus
Rickettsial disease in US
In the United States, rickettsial diseases that are transmitted by ticks include Rocky Mountain spotted fever (RMSF) due to Rickettsia rickettsii; “mild” RMSF (Rickettsia parkeri and other spotted fever group Rickettsia spp), human granulocytic ana- plasmosis (Anaplasma phagocytophilum), human monocytic ehrlichiosis (Ehrlichia chaffeensis), and ehrlichiosis caused by Ehrlichia ewingii or Ehrlichia muris
HIV detection timeline
After exposure to HIV, HIV RNA is detectable in plasma by 10–12days, followed by appearance of HIV p24 antigen in serum or plasma at 15–17days.
HIV-specific antibodies are detect- able in serum or plasma at the earliest at 21days after exposure
In the neonate, serologic testing is unreliable due to per- sistence of maternal antibodies
HCV genomic testing for resistance
Pretreatment testing for HCV genome-specific resis- tance-associated substitutions (RASs) by conventional (Sanger) or next-generation sequencing assay methods is recommended by the FDA and/or current clinical practice guideline (https:// www.hcvguidelines.org/evaluate/resistance) prior to initiating certain DAA therapy combinations for infection due to certain HCV genotypes: (1) HCV NS3 RAS for simeprevir in genotype 1 infection, and (2) HCV NS5A RAS for elbasvir-grazoprevir or ledipasvir/sofosbuvir in genotype 1a infection, and daclat- asvir/sofosbuvir or velpatasvir/sofosbuvir in genotype 3 infec- tion.
ESR normal range
<30 (exact cutoff depends on age and gender)
CRP normal range
<7.5
