Sample Collection

Samples for SARS-CoV-2 testing are collected from untreated wastewater or sludge. Wastewater treatment plants are the most convenient sources for sampling, as they routinely collect samples for operational monitoring. For more specific information on SARS-CoV-2 transmission within communities, upstream sampling from pump stations or manholes can be conducted, although this typically requires a specially trained team.

Standard safety procedures, including handwashing and wearing necessary personal protective equipment, ensure safe sample collection. The CDC has found no evidence of COVID-19 infection from exposure to wastewater.

Sampling Strategy & Process.


Sampling points are chosen based on factors, such as the size and nature of the upstream population, the relative contribution of residential, commercial, and industrial wastewater to the plant's input, and the capacity of treatment plant personnel to manage samples. For instance, sampling points with a high proportion of residential properties are more likely to accurately reflect SARS-CoV-2 transmission trends compared to those with mostly commercial or industrial areas.

Selecting Sampling Points.

Sampling Frequency.

To provide actionable and timely data on COVID-19 transmission changes, twice-weekly sampling is recommended. If resources are limited, a minimum of once-weekly sampling is advised. While a single sample can confirm the presence of SARS-CoV-2, a series of multiple samples from the same point is needed to reveal transmission trends.

Sample Types.

Two common sample collection methods are composite sampling and grab sampling.

  • Composite samples are collected using automated samplers, which take small quantities of wastewater continuously or at intervals to create a composite sample over a set period, usually 24 hours. This method captures variations in wastewater flow and composition throughout the day. This is the preferred method for the NYS Wastewater Surveillance Network.

  • Grab samples, which are easier to collect, involve filling a collection bottle at a single time point without specialized equipment. While grab sample results often align with composite sample results, they are more sensitive to fluctuations in wastewater composition due to daily routines, weather, or other factors.