TRC Talks – Air Testing for the Virus that Causes COVID-19

Yes, it is possible to measure SARS-CoV-2 and related viruses in ambient air, on solid surfaces and in wastewater.

A special prepackaged swab in a screw-cap vial containing a buffer solution is used to collect samples. The swab is connected to the vial cap and is used to swab a small surface in a zig-zag pattern. After waiting about 10 seconds, the same area is swabbed again. The swab is returned to the vial and shipped to our lab for analysis.

We use a standard personal sampling pump and preloaded polytetrafluoroethylene (PTFE) filter cassettes (0.3 um, 37mm). The flow rate is 2.5-5 liters per minute (lpm) for 4 to 6 hours and collects a sample volume of about 1,000-2,000 liters on an open face cassette. The filter cassette is then returned to the lab for analysis.

Extensive research indicates that these PTFE filters are efficient for collecting submicrometer and nano-scale aerosol particles, including bacteria and viruses. In tests, this specific 0.3-μm PTFE filter with a 37-mm, three-piece cassette, exhibited the lowest pressure drop and highest collection efficiency for virus particles. Alternative sampling methods are also available.

Wastewater samples are collected using an autosampler to collect a composite sample over a time period representative of the building population profile. Collection can be either flow-proportional or time-dependent.

Ambient air, surface and wastewater samples are analyzed by reverse transcriptase polymerase chain reaction (RT-PCR). This is the same technology used in detecting the COVID-19 virus in clinical settings. Tissue culturing techniques require the presence of infectious viruses and take several days to complete, while RT-PCR requires only viral RNA and testing is complete within hours.

We offer air, surface and wastewater testing as qualitative methods. Because there are not regulatory limits for SARS-CoV-2 levels in environmental samples, we see value in reporting measurement data as positive or negative for SARS-CoV-2 detection. In other words, our report will indicate the presence or absence of targeted viral agents in the sample.

Our approach measures SARS-CoV-2 residues so what we measure does not translate into infectious genome copies of the virus. Our data simply indicate that SARS-CoV-2 residues are present in the sample, not that the genome copies we measure are infectious.

This is important to understand. It is possible that an infectious form of SARS-CoV-2 is collected during sampling but rendered noninfectious by environmental factors or sampling technique; however, this technique can still detect the SARS-CoV-2 RNA unless it has been completely destroyed.

Our lab partners are offering 24- and 48-hr TAT for samples, based on current analytical reagent availability. This means that if a sample is collected on Monday and shipped for arrival at the lab on Tuesday morning, the results can be reported early Wednesday morning. Analysis of samples on weekends or the day of receipt is also available but must be scheduled in advance.

The surface sampling method for SARS-CoV-2 can be used to support cleaning and disinfection (C&D) programs. For example, after verifying that C&D were performed with the proper cleaners and disinfectants in accordance with label directions and the C&D plan, samples would be collected for SARS-CoV-2 analysis. When used with adenosine triphosphate (ATP) swab sampling, which provides real-time data about the presence of biological residues, SARS-CoV-2 sampling can provide an additional level of confidence about the effectiveness of C&D.

The air sampling method is not intended to support a C&D verification program and is not suitable for monitoring a space where the facility has no control of the workspace and worker population. Consider the case of the Triumph Foods meat packing plant in Missouri, where 375 asymptomatic workers tested positive for COVID-19 (17% of the work force).

Temperature screening isn’t going to detect asymptomatic workers. If sampling equipment is installed in areas where employees congregate for short periods of time, it may be possible to detect increases in airborne concentrations of SARS-CoV-2 residuals. For example, sampling in areas where employees clock in and out could yield actionable information about changes in measured SARS-CoV-2 concentration intensity. In short, the air sampling method is part of a long-term monitoring strategy intended to supplement other protocols that detect symptomatic workers.

Wastewater sampling applications are similar to those for air monitoring. Regular and ongoing monitoring of wastewater effluent can provide an early indication of SARS-CoV-2 outbreak in a population, possibly even while occupants are asymptomatic but potentially contagious.

No, because ATP testing focuses on biological residues that use ATP to fuel biochemical processes. SARS-CoV-2 testing (RT-PCR) focuses on measuring residual viral RNA. However, ATP testing performed in advance of SARS CoV-2 testing can provide real-time data about the effectiveness of C&D programs, allowing repeat C&D if ATP testing fails, and thereby increasing the probability of a desired negative SARS-CoV-2 test result.

Trained individuals familiar with industrial hygiene and environmental sample collection protocols must collect the samples. TRC’s field technicians, working under the direction of a Certified Industrial Hygienist (CIH), understand the sampling equipment and protocols and have received training in those protocols, as well as COVID-19 and bloodborne pathogens. TRC’s technicians participate in our medical monitoring program and are medically fit to wear a respirator, in accordance with our respiratory protection program. Respiratory protection may be required when certain C&D materials are used. If desired, TRC can provide training for facility personnel in the proper collection and shipment of surface, air and wastewater samples.

Our laboratories are accredited to ISO 17025, General Requirements for the Competence of Calibration and Testing Laboratories.

Each test is comprised of two components: sampling and analysis. The cost for sampling will be site specific and reflect the typical costs associated with deploying a field technician and sampling equipment. The analytical cost for a single sample, based on current analytical reagent availability and pricing, which includes media and shipping, is approximately $300 for 24-hour turnaround and $200 for 48-hour turnaround. We’ve seen cost reduction as the analytical technology has evolved. Additionally, significant discounts are available for multiple samples. Please contact us for current pricing and availability based on your project needs.