Table 2.

Key elements of a false-negative mitigation plan.

Element	Corrective actions
Sampling	Use composite sampling where applicable; For grab sampling applications, multiple sampling events over a few hours during morning to midday period may be useful.
	Seeding wastewater samples with appropriate process control material. Use multiple sample replicates to confirm results.
	Collect multiple sample replicates to confirm results.
Sample storage	Proper storage conditions during transport and prior to processing.
	Avoid storing bulk samples and minimize freeze-thaw cycles where possible.
	Minimize storage time prior to concentration.
Virus concentration	Optimization of concentration method using appropriate surrogate and local wastewater.
	Include process control to assess recovery efficiency.
	Consider concentrating virus from both liquid and solid phases of wastewater.
RNA extraction	Assess RNA quality and yield before testing.
	Seed molecular process control to assess extraction efficiency.
	Validation of extraction method with appropriate surrogate.
PCR inhibition	Inhibition molecular process control or dilution to assess potential inhibition effects.
RT-qPCR or -dPCR amplification	Confirm assay sensitivity using local wastewater samples seeded with appropriate control material.
	Analyze multiple replicates for trace detections.