by Felisha Pierre-Louis, Senior Product Manager, and Konrad Knauss, Product Manager, Thermo Fisher Scientific
Large-scale diagnostic testing remains at the heart of global efforts to confront the spread of the SARS-CoV-2 coronavirus.
The availability of rapid and reliable diagnostic tests for COVID-19 has proven critical during the pandemic, reducing onward infections through contact tracing measures. The early identification of positive cases has been particularly important given the significant contribution of asymptomatic transmission to overall rates of infection. Despite the impressive pace of national vaccination programs in recent months, concerns over the emergence of more vaccine-resistant variants mean diagnostic testing will continue to be a major part of the long-term strategy for pandemic management.
Extending the capacity and ensuring the accuracy of COVID-19 testing have been key priorities for diagnostic laboratories. However, the pandemic has also underlined the importance of establishing safe and reliable workflow methods for the handling of test samples. With hundreds of thousands of positive cases recorded globally each day, without robust workflow methods for the prevention of accidental exposure to the virus, each new specimen potentially puts the safety of laboratory professionals at risk.
Virus Inactivation: An Essential Step in COVID-19 PCR Testing
The two diagnostic approaches most commonly used for detecting active COVID-19 cases during the pandemic have been antigen testing and polymerase chain reaction (PCR) testing. Antigen testing, the faster of these techniques, detects protein fragments specific to the SARS-CoV-2 virus, and is capable of returning results in as little as 15 minutes. PCR testing detects coronavirus RNA, and while turnaround times are longer (1–3 days), the test is more commonly used due to its lower rate of false-positive results.
Virus inactivation is a key step in PCR testing workflows, vital to protecting medical laboratory personnel from infection through accidental exposure to samples. While several strategies for virus inactivation are available, including the use of UV light and chemical reagents, many laboratories deactivate the SARS-CoV-2 coronavirus using heat. Typically, vials containing test samples are loaded into a microbiological incubator or oven and exposed to temperatures of between 56 °C and 65 °C for a minimum of 30 minutes1, with several recent studies recommending temperatures at the higher end of this range.
To ensure effective heat inactivation, care must be taken to avoid overheating samples, which can reduce the amount of detectable virus RNA and potentially lead to false-negative results. Underheating samples, on the other hand, risks incomplete virus inactivation, leaving laboratory teams vulnerable to accidental exposure. Using heating technologies that provide precise temperature control are therefore critical.
Advanced Microbiological Incubators: Precise Temperature Control for Heat Inactivation
When it comes to heat inactivation, diagnostic laboratories typically have two options, which provide differing levels of temperature control.
The traditional solution for heat inactivation is the laboratory oven. Most laboratory ovens are capable of operating over a very broad range of high temperatures, typically between 50 and 330°C. However, while ovens are highly effective for high-temperature applications, such as annealing, drying and sterilization, they can be less effective when precise temperature control is required, as their powerful heating elements and internal fans can create temperature fluctuations.
Advanced microbiological incubators, on the other hand, offer a more controlled environment for virus heat inactivation. By carefully regulating conditions such as temperature, high-end microbiological incubators provide very precise temperature control over a more focused range of moderate temperatures (typically 27–105°C). This enhanced control means microbiological incubators maintain temperature drift to around 0.1°C, ensuring superior uniformity and stability of conditions.
Implementing Best Practice for Complete Virus Inactivation
The effectiveness of viral heat inactivation processes can be further enhanced by the application of good laboratory techniques. One of the best ways to maintain consistent sample heating is by loading the microbiological incubator evenly. While a partially filled chamber will heat up faster than a fully loaded one, samples in a fully stocked chamber benefit from being surrounded by other vessels, and will be better able to maintain a stable temperature. A fully loaded incubator chamber will, therefore, enhance virus inactivation by ensuring specimens are exposed to the same temperature regardless of where the sample is positioned.
With potentially thousands of specimens to inactivate every day, batches of samples will continually be transferred in and out of the incubator chamber. With so many samples for laboratories to test, it is extremely important that this changeover occurs as quickly as possible, as leaving a door open for longer than is necessary can allow a substantial quantity of heat to escape. Not only is this inefficient — requiring the unit to re-heat to reach the appropriate temperature — it also leaves samples vulnerable to uneven temperature distribution within the chamber, running the risk of incomplete virus inactivation. Fortunately, ongoing improvements in advanced microbiological incubator design are helping diagnostic testing laboratories strengthen the integrity of their sample handling workflows to better protect their teams.
Safer Sample Handling through Advanced Microbiological Incubator Design
With enhanced ease of use key to driving improvements in sample handling safety, equipment vendors have responded to the needs of diagnostic laboratories by developing solutions to ensure a safer working environment. Modern high-end microbiological incubators now offer a range of features to support usability, including audible alarms that alert users to open doors and internal temperature deviations. Additional innovations, such as secure, lockable doors, serve to enhance the integrity of samples and test results by restricting unauthorized access.
Other advances in high-end incubator design are improving laboratory safety by making aseptic sample handling procedures quicker and easier to utilize. Some advanced microbiological incubators, for example, feature high-temperature chamber decontamination cycles that can be started at the push of a button, streamlining their operation within busy PCR testing workflows. By making decontamination cycles as convenient as possible, these important innovations help to minimize virus cross-contamination, while supporting faster turnaround times and continuous operation to deliver PCR test results in the shortest possible time.
Protecting the Safety of Laboratory Teams during the COVID-19 Pandemic
Throughout the COVID-19 pandemic, scientific professionals have worked tirelessly to perform the diagnostic tests that have become so critical for protecting public health. However, without safe and reliable workflow methods for the handling of PCR test samples, each of the thousands of specimens received by laboratories every day puts the health of these teams at risk. High-end microbiological incubators have proven highly effective for delivering the precision temperature control necessary for reliable virus heat inactivation in PCR workflows, and thanks to ongoing improvements in design, the latest solutions continue to enhance the integrity of sample handling workflows, ensuring a safer laboratory environment in which to protect public health.
References
1. MER Darnell et al, J Virol Methods, 2004, DOI: 10.1016/j.jviromet.2004.06.006