Environmental Monitoring & Assessment Flashcards

An environmental swab is weakly positive (Ct 38) while its replicate is negative. What is the best interpretation?

Answer: Low-level or stochastic signal near the limit of detection; re-swab and retest

Inconsistent late Ct values near the LOD reflect stochastic sampling and should be confirmed by repeat testing.

Which practice most reduces aerosol generation when opening tubes containing amplified product?

Answer: Briefly centrifuging tubes and opening them carefully, away from clean areas

Spinning down collects liquid from the caps, and opening gently in the post-PCR area limits aerosols.

A lab finds amplicon contamination in its pre-PCR hood. Which step should come FIRST?

Answer: Stop testing in that area, decontaminate, and investigate the source

Containment and investigation must come before testing resumes, so contaminated results are not reported.

Aerosol-resistant (filter) pipette tips are used in PCR setup primarily to:

Answer: Prevent aerosols from contaminating the pipette barrel and later samples

Filter barriers stop aerosolized nucleic acid from entering the pipette shaft and spreading to later samples.

When choosing locations for environmental swab monitoring, which site has the highest priority?

Answer: High-touch surfaces like pipettes, centrifuge lids, and hood work surfaces

High-touch surfaces in the work areas are where contamination most likely builds up and spreads into reactions.

Why should lab coats used in the post-PCR area never be worn into the pre-PCR area?

Answer: They can carry amplicons that contaminate clean reagents and setups

PPE worn in amplification areas collects amplified DNA and moves it into clean zones.

A trend chart shows NTC Ct values moving from undetected to Ct 36, then Ct 33 over several weeks. This pattern suggests:

Answer: Contamination building up that needs investigation before it affects results

Earlier and earlier NTC Ct values mean a growing contaminant load in the lab or reagents.