Validating Cleaning Efficacy for Removal of SARS-CoV-2: FACS Update #4


The number of COVID-19 cases in America continues to rise. So have questions regarding keeping families, co-workers and the general public safe. Public health organizations such as World Health Organization (WHO) and Centers for Disease Control and Prevention (CDC) provide recommendations for cleaning and disinfection related to the virus responsible for COVID-19 infections, SARS-CoV-2. But there is a lack of information regarding how to validate that cleaning and disinfection efforts were effective. Stakeholders want proof the work done made the environment safe. Investigators and restoration contractors alike wrestle with the options and opinions but there is a lack of consensus regarding the best way to prove response actions were successful. Understanding the methods that are available and knowing if they are effective can be daunting and confusing to consumers.

Assessing the effectiveness of cleaning and disinfection involves an industrial hygiene (IH) assessment. An IH assessment: can include gathering detailed observations; developing a site-specific case history; review of information/documents; and perhaps environmental sampling. Sampling alone is rarely an effective method for determining successful remediation.  Verification that remediation efforts were adequate in removing or killing the Coronavirus can be complex especially with the known limitations associated with environmental sampling. Some protocols can be useful in determining if environmental conditions have improved by the actions taken, but to date there is no known method available for environmental sampling of surfaces that has been proven to verify efficacy for the removal of SARS-CoV-2. Most studies available include a statement such as “It is important to note that negative environmental testing results cannot exclude the presence of virus within the setting where the investigation has been conducted.”1

Various surface testing methods may be considered, each with its own benefits and limitations. Key factors when considering environmental sampling include:

  • Is the method specific to the agent of concern?
  • Are results obtainable onsite or is laboratory analysis required?
  • How easy is sample collection?
  • Are we trying to prove if cleaning was done properly or if the virus is no longer present?
  • Where and how many samples should be collected?
  • What results will be considered acceptable?

While the following will address some of the science involved, it is only offered to describe value and limitations of methods and is not intended as a detailed discussion of the methods.

The first issue of surface testing is the specificity to test for the virus. Currently there are both field and lab tests being considered that are classified as “surrogate” methods while others are virus specific testing methods that require laboratory analyses. Surrogate methods look for something other than the virus. This could include compounds present in organic matter such adenosine triphosphate (ATP) or specific bacteria or bacterial indicators that are commonly found in the environment. ATP testing can be done in the field, while other methods require lab analysis of samples collected. Bacterial surrogates can include organisms that are killed by the same disinfectants that kill viruses and may even be more resistant to the biocides. One important limitation is that these methods are not specific to virus, but a common assumption is that if the surrogate has been reduced, a similar reduction in virus has occurred. Another limitation of these methods is without a large number of organisms present it is difficult to determine if adequate reduction occurs. To confirm desired reduction of the agent, which may be reducing numbers by 10,000, 100,000 or 1,000,000 times or more, requires knowing that millions of surrogate organisms were present prior to cleaning and disinfection.

Improvements in existing methods and introduction of new methods, including some developed specifically for use in detecting SARS-CoV-2 on environmental surfaces are occurring at a rapid pace. Some laboratory tests may take up to five days or more and may not be practical if results are needed sooner. Polymerase chain reaction (PCR) analyses may be completed much faster, but also have significant limitations when trying to assess for effectiveness of disinfection.  These methods can be targeted directly to the virus in question but as noted above, absence of positive results does not mean absence of virus.

Having a good cleaning/disinfection plan in place is essential. On-site monitoring of the work performed should be part of that plan. Currently, validation for the effectiveness of response actions should start with the following elements in place:

On-site monitoring and documentation should be performed by someone that is not responsible for performing the cleaning or disinfection activities. This individual should be familiar with the site-specific plan and best practices. Sampling of various surfaces may be a useful supplemental tool but at this time, environmental sampling is generally limited to determining if the work area is cleaner after the work is done (success) or if viruses may still be present (failure) as opposed to determining the absence of the virus.

As research continues and new methods are developed, it is important to recognize that the most essential elements for validation may not include sampling. Until environmental sampling methods are scientifically supported and include the types, numbers and locations of samples as well as criteria for interpreting sample results, validation of cleaning and disinfection should rely more heavily on on-site monitoring and documentation of work practices than on collection of environmental samples.

The experts at FACS are here to help. We will continue to provide updates with information and experiences we feel may be valuable. Please contact us if you have any questions or if our experts can be of assistance in managing your response.

1 Surface sampling of coronavirus disease (COVID-19): A practical “how to” protocol for health care and public health professionals. World Health Organization. Version: 1.1. Date: 18 February 2020