Research and analysis

Position statement on inactivation of SARS-CoV-2: Implications for laboratory testing

Updated 9 June 2021

1. Main points

Public Health England’s (PHE) High Containment Microbiology department is investigating the efficacy of SARS-CoV-2 inactivation by different methods and by commercial products.

The investigation does not consider any other biological agents that may be present in diagnostic samples so additional inactivation steps may be required in such circumstances.

Inactivation reagents should not be assumed to be 100% effective against SARS-CoV-2. Any additional precautions required for the safe handling of SARS-CoV-2 samples following inactivation must be considered in risk assessment.

All COVID-19 laboratory testing workflows must be subjected to suitable and sufficient risk assessment, with consideration given to any inactivation step.

Risk assessments must be reviewed regularly as new information on the inactivation of SARS-CoV-2 becomes available.

The impact of the chosen inactivation method on the sensitivity of subsequent SARS-CoV-2 detection should also be assessed locally.

2. Background

Many commercial inactivation reagents and treatments are compatible with subsequent SARS-CoV-2 RNA extraction and molecular testing. However, evidence of the effectiveness of these methods for SARS-CoV-2 inactivation is required to ensure safe downstream handling of sample extracts and to inform risk assessments associated with these procedures.

PHE’s High Containment Microbiology department is evaluating the efficacy of SARS-CoV-2 inactivation treatments including commercial molecular lysis buffers, detergents and heat (and combinations of these). Studies use a range of sample types, including tissue culture fluid and clinical material.

We determine the reduction in SARS-CoV-2 titre following test treatments and interpret results using the British Standard for quantitative suspension tests for evaluation of virucidal activity, which requires that disinfectant products demonstrate a titre reduction of at least 4 log in virus titre ^{[footnote 1]}.

We also determine whether infectious SARS-CoV-2 virus can be recovered from treated samples following passage in cell culture.

The effectiveness of inactivation treatments is influenced by many factors including:

• the nature of the sample
• the amount of infectious pathogen within a sample
• volume of sample added per volume of product/final concentration of active ingredients
• total volume of sample (for heat inactivation)
• treatment time
• treatment temperature
• method of mixing of sample and product

These factors must be considered when using data from inactivation studies to risk assess laboratory testing procedures.

Choice of inactivation method is a local decision. It should be supported by a suitable and sufficient risk assessment for the entire COVID-19 diagnostic workflow. Choice should also consider impact on RNA integrity to ensure that the inactivation procedure does not adversely affect the sensitivity of the laboratory’s downstream molecular test(s).

Queries regarding High Containment Microbiology (HCM) inactivation testing should be directed to HCMgroup@phe.gov.uk

1. British Standards Institution, Chemical disinfectants and antiseptics – Quantitative suspension test for the evaluation of virucidal activity in the medical area – Test method and requirements (Phase 2/Step 1). 2019, BSI Standards Limited. ↩