Virucidal Efficacy Testing


In the United States, the U.S. Food and Drug Administration (FDA) ensures the safety and efficacy of over-the-counter (OTC) antiseptic products, such as hand rubs and hand washes. The FDA has issued a final ruling on the evaluation of antiseptic products which includes a determination regarding actives and their categorization as generally recognized as safe (GRAS) and generally recognized as effective (GRAE). This ruling relates specifically to hand washes, which are intended to by used with water, and makes no mention of viral efficacy requirements. Within the same ruling the FDA does acknowledge that transmission of pathogenic viruses may occur due to contact with contaminated hands or surfaces. Currently there is no protocol recognized by the FDA to specifically confirm the virucidal efficacy of health care personnel hand washes or hand rubs, but Vivo Clinical Testing can provide virucidal efficacy testing services for clients that wish to assess the virucidal properties of their test articles. 

Virucidal Efficacy Testing Is Different - Here's How:

Testing Basics

Virucidal disinfectants for use on non-porous surfaces may be registered through the EPA. The EPA currently only recognizes "hard surface carrier" methods for substantiation of virucidal efficacy claims. These methods consist of a non-porous carrier (typically glass) being inoculated with the selected virus, dried, and then treated with the disinfectant. Virucidal hard surface carrier methods are quantitative, meaning that percent and log reductions are calculated by determining the TCID50 (50% Tissue Culture Infective Dose) per carrier before and after treatment with the disinfectant. The disinfectant must demonstrate complete inactivation of the virus down to the limit of detection of the assay, corresponding with a ≥ 3.00 log10 reduction (99.9%).

The FDA does not currently recognize virucidal claims for hand sanitizers, and does not provide guidance related to virucidal testing for healthcare personnel hand washes, hand rubs, or other Over-The-Counter (OTC) topical antiseptics. 

Observation of Results

Virus testing is unique within the laboratory because the presence of viruses before and after product treatment is not determined by observing growth of virus but rather by observing the damage caused by infection to mammalian host cells. When virologists analyze individual sets of cells after a study, they use a microscope to look for where healthy cell layers become damaged. This damage is known as the cytopathic effects (CPE) of infection. The quantity and quality of CPE is used to calculate the amount of virus present.

cell culture flasks

CPE is typically observed as changes to cell appearance and monolayer (the layer host cells form when they attach to a flask or tray) disruptions. CPE can vary depending on the virus and host cell line used. Some instances of CPE are distinct, consisting of severe monolayer disruption and cell rounding. Some CPE can be subtle, consisting of gradual enlargement of host cells that is only recognizable when compared to a negative control. In cases where CPE is difficult to distinguish, special confirmatory assays are used to verify the results of the assay. Some more common confirmatory assays include Hemagglutination Assays (HA) and immunofluorescent staining (IF).

Study Preparation and Timeline

From the laboratory's perspective, a significant amount of work and time is required to grow and maintain the sterile cell cultures that are needed to propagate and detect viruses in antimicrobial efficacy studies. From our customer's point of view, the cell culture requirement means that extra time must be given to the laboratory to prepare for and execute the study. Most preliminary efficacy studies take 1-2 weeks to complete, though some can take significantly longer. The behind-the-scenes cell culture work and extraordinary expertise necessary to conduct virological assays also means that virological studies are generally more expensive than their related bacteriological assays.

Study Conduct and Parameters

There are two main viral morphologies - enveloped and non-enveloped. Non-enveloped viruses consist of genetic material surrounded by a hard protein coat. Enveloped viruses have an additional lipid layer encompassing their protein coat. The limited sensitivity of non-enveloped viral components means that these viruses can persist in an infectious state even when exposed to harsh environmental conditions - including exposure to UV or relatively high temperatures. When it comes to testing, this means that one can translate almost any bacteriological study into a non-enveloped viral assay without changing too many parameters.

Enveloped viruses are another story. Their delicate lipid envelopes leave them vulnerable to environmental factors like osmotic pressure, low humidity, and high temperatures. When working with enveloped viruses, certain parameters (like contact times and contact temperatures) and even general study methods may need to be modified to accommodate the unique demands of these microbes.

Viruses Tested at the Laboratory*

  • Feline Calicivirus (approved Human Norovirus surrogate)
  • MS2 Bacteriophage

* Vivo Clinical Testing is happy to acquire additional viruses to meet your testing needs.  Contact us today to discuss viral acquisition and your testing options.