Other control measures such as shelter-in-place orders, strict quarantines, and isolating positive cases can be effective, and all have been used to varying degrees in many locations. Famously, the city of Wuhan, China, implemented a strict quarantine for over a month with extreme limitations on citizens’ movement. At the time, this measure seemed draconian to Western governments and citizens, but the city reopened within two months while much of Europe and the U.S. have fought protracted battles for over a year. Similar but less severe limitations were instituted in Italy, Spain, and New York City following rapid rises in cases at the beginning of the pandemic. New Zealand and Australia were able to keep their case numbers low by severely restricting incoming travel, enforcing two-week quarantines of arriving travelers and requiring negative COVID test results before release. With a lack of scientific evidence specific to SARS-CoV-2 and the need to make swift decisions, governments chose policies they could enact both broadly and quickly. After initial control measures were implemented, permanent engineering controls were explored such as upper-room germicidal ultraviolet (GUV) light, in-room high efficiency particulate air (HEPA) filtration, and increased dilution ventilation along with higher minimum effective reporting value (MERV) filters. However, improving the indoor infrastructure of whole nations in one season was just not feasible. Sampling strategies are a core tool of industrial hygiene, and environmental sampling in particular is used to evaluate hazard controls. Without analytical support capable of measuring SARS-CoV-2, it was difficult to formulate any nuanced approaches based on benchmarks of virus load or known transmission dynamics. There is still no consensus on the infectious dose of this virus other than a vague directive that fifteen minutes of exposure to an infected person is sufficient to cause infection in a susceptible individual. Determining if a control is “good enough” is therefore difficult. Nonetheless, there is still much value in knowing the level of risk reduction provided by certain control measures and policies. TYPES OF TESTING The early months of the pandemic saw the development of rapid and accurate tests for SARS-CoV-2 in human specimens, and tests were also quickly developed for analysis of these viruses in environmental samples such as air and surface samples. By June 2020, AIHA Laboratory Accreditation Programs (AIHA LAP) began offering accreditation for reverse transcription, quantitative, polymerase chain reaction (RT-qPCR) testing of SARS-CoV-2 under its microbiology program, and several accredited microbiology labs have since added this type of molecular testing to their scopes. This development has provided IHs and decision-makers with the analytical support necessary to make informed policy decisions. Detection of the SARS-CoV-2 virus is primarily performed using RT-qPCR. One advantage of RT-qPCR is that it can be made highly specific by using primers that bind to unique DNA segments. As SARS-CoV-2 is an RNA retrovirus and therefore does not have DNA segments, the assay first converts the viral RNA into DNA using reverse transcription. Next, the primers bind to a segment of DNA unique to the virus and the polymerase enzyme begins replicating that portion of viral DNA. A fluorescent molecule is released from each primer when it binds to DNA; therefore, the sample’s fluorescence is related to the number of DNA replications, which is a function of the number of RNA copies at the start of the reaction and the number of replication cycles. The assay can be quantitative, semi-quantitative, or qualitative depending on how the amplification profile is interpreted. The simplest case is the qualitative assay, which indicates the presence or absence of viral DNA. If a sample yields fluorescence above background, then virus was present in the sample. For semi-quantitative analysis, the number of replication cycles needed for the virus to become detectable is compared between samples. Since each replication cycle doubles the number of viral DNA segments, a sample that takes 25 cycles for the virus to become detectable is expected to have 27 times more virus than a sample that takes 32 cycles. For quantitative analysis, the lab must make a calibration curve from a series of known concentrations of viral samples to determine the detection limit of the assay and relate that to the number of replication cycles. Clearly, qPCR is the most stringent and difficult PCR analysis for the lab to conduct. While highly specific to SARS-CoV-2, PCR-based analysis cannot differentiate between viable and non-viable virus. To differentiate between viable and non-viable virus, two different assays are commonly used: an endpoint dilution assay, commonly referred to as median tissue culture infectious dose 50 percent (TCID50); and a plaque assay. A simple explanation of TCID50 is that it estimates the virus concentration from the amount of sample needed to infect a cell culture. In plaque assays, cells in plates become infected with a virus; the virus replicates and spreads to other cells, forming a plaque, or area of cell death. Counting the number of plaques is a common method to determine virus concentration. Sample results are usually reported as plaque forming units per milliliter (PFU/mL), which can be converted to PFU/m3 by using sampled air volume and virus extraction volume. In TCID50, host cells are cultured in a well plate with liquid medium, and then dilutions of viral fluid are added to the wells and incubated. The end measurement is the percentage of infected wells for each dilution. The rule of thumb is that the PFU/mL concentration is 70 percent of the TCID50 concentration, as TCID50 is more sensitive (and more variable). Neither technique is commonly available outside of research arenas due to their highly specialized nature and the need to maintain virus viability throughout the assay. During the pandemic, plaque assays have been hard to source due to supply chain issues; therefore, TCID50 has been the most commonly used assay for cultivability testing of SARS-CoV-2. For agents like SARS-CoV-2, which must be handled in facilities certified as biosafety level 3 (BSL-3), stringent safety precautions, training, facilities, and government approval are required. These factors make both types of live culturing for SARS-CoV-2 prohibitively costly. The alternative to live culturing is PCR analysis of environmental samples. While PCR analysis has quickly become standardized and more widely available, environmental sampling approaches are still emerging as a new tool in the response to SARS-CoV-2. In the remainder of this article, we will briefly explore the variety of air and surface sampling techniques currently available for SARS-CoV-2. SAMPLING TECHNIQUES Just like any other particulate contaminant, viruses can be efficiently collected from a surface with a swab or wipe and captured from the air with simple filtration or impingement. However, industrial hygienists must consider the compatibility of both the sampling technique and the analysis technique, along with the effect of sampling stresses on the target organism. For surface sampling, it is necessary to remember that the analysis procedure is adapted from nasopharyngeal swabs, so using a ghost wipe instead of a swab may not be compatible with the lab’s extraction process. It is also possible that the wipe matrix or chemical additives may interfere with the RT-qPCR reaction. Any sampling matrix should be validated by the laboratory; therefore, it is best to consult the laboratory before collecting samples to ensure you use the same swab or wipe that they have already validated. Swab sampling is usually conducted on a relatively small surface area (approximately 25 cm2) with a moistened nasal swab. This technique applies the same principles as any wipe sampling: thoroughly wipe the whole area vertically and horizontally while rotating the swab to use its entire surface. Mark a standard area or estimate the area of the swabbed object (such as an elevator button, door handle, or finger). After sampling, the swab is usually placed into a sterile container with a transport medium or nucleic acid fixative.