Evidence Briefs

Provide a synthesis of the best available evidence on a variety of priority topic areas as identified by leading infectious disease experts. We systematically explore the published literature using a comprehensive search strategy to identify relevant research on infection prevention, management, and control. For more information on our search strategy of the published literature, click here.
McMaster University
NCCMT

Virus Stability

Mar 28, 2017

Author(s): Stephanie Vendetti-Hastie, RN, CIC, Kristin Read, MPH, & Dr. Maureen Dobbins, PhD, RN
Expert Reviewer(s): Dr. Mark Loeb, MD, MSc, FRCPC & Dr. Dominik Mertz, MD, MSc

The OutbreakHelp Evidence Briefs aim to provide short summaries of the available evidence related to priority topic areas identified by leading infectious disease experts. Content for the Evidence Briefs were developed using a comprehensive and systematic search of the academic literature from inception to December 31st 2015 (more recently published information on this topic may be available here). All results were screened for relevance using pre-defined inclusion and exclusion criteria. Included articles must have met the following criteria: 1) specific to the topic of Ebola Virus Disease (EVD), 2) human research or research with real-world applicability, 3) study in a peer reviewed journal, and 4) published in either English or French. Articles identified as relevant were tagged with priority topic areas and assessed for quality using abbreviated versions of appropriate critical appraisal tools; a 5-star rating scheme was applied to articles as relevant. Relevance screening, category tagging, and critical appraisal were independently conducted by two raters and conflicts were resolved through discussion. A thematic analysis was performed on included articles by charting and then categorizing common concepts and topics discussed in the literature. Results are summarized in a narrative. The following Evidence Brief discusses environmental considerations focusing specifically on EVD stability in liquid media and on solid substrates.

Main Message

In the absence of visible contamination, EVD has been detected by reverse transcription polymerase chain reaction (RT-PCR) on some fomites commonly found in patient care environments and in close proximity to the immediate patient bedside.

In experimental conditions in a lab setting, EVD has been recovered in varying levels from liquid media (e.g. guinea pig sera, tissue culture media, water, blood) when stored at temperatures ranging from 4°C to 27°C, for periods up to 46 days (tested at day 0, 26, and 46). Survival during storage at lower temperatures was longer than at higher temperatures.

When dried onto various solid substrates such as glass, plastic, polyethylene fibre, cotton and possibly some metal alloys, the virus has reported to have been recovered, in varying levels, after lengths of time ranging from < 24 hours up to 50 days and at temperatures ranging from 4°C to 27°C.

When suspended in an organic soil load the virus showed prolonged environmental persistence (up to 196 hours) on some surfaces common to a clinical setting (surgical mask, plastic gown and steel).

One major limitation of many studies was the use of RT-PCR because detection of viral nucleic acid does not confirm virus viability

Virus Stability in Liquid Media and on Solid Substrates

Piercy et al. (2010) assessed EVD variant Zaire (ZEBOV) in two types of liquid media, guinea pig sera and tissue culture media, over a period of 46 days. Samples were stored at either 4°C or room temperature at a relative humidity (RH) of 55+/- 5% and were assessed on days 0, 26, and 46. There was no significant difference in survival of the virus in either guinea pig sera or tissue culture media. Results indicate that samples stored at 4°C showed that virus viability reduced in level by a maximum of 2-3 logs on day 26, and more rapidly (4 logs) in samples stored at room temperature. On day 46 virus levels of all samples were just above the test detection limit. There was a significantly different survival in liquid media during storage at 4°C compared with storage at room temperature (P < 0.001, two-way ANOVA) (Piercy, et al., 2010).

In addition to liquid survival studies, Piercy et al. (2010) also studied stability of ZEBOV in guinea pig sera and tissue culture media dried onto glass, plastic and metal at different temperatures. ZEBOV could not be recovered from any substrate stored at room temperature nor from metal substrate at any time (day 2, 7 and 14) (Piercy, et al., 2010).  Overall, ZEBOV dried onto solid substrates and stored at 4°C was recovered in high levels from both plastic and glass surfaces over a 14 day period, with levels decreasing over time. In samples dried on glass, the virus could be recovered at fairly high levels on day 26 and for tissue culture media samples the virus was detectable at low levels on day 50. There was no significant difference in the recovery of the virus suspended in either sera or tissue culture media dried onto glass or plastic (Piercy, et al., 2010).

Fisher et al. (2015) studied the stability of Guinea Ebola Virus (EBOV) Makona variant in various liquid media including water, human blood, and the blood of infected non-human primates. Experiments were conducted in two environmental conditions, 21°C, 40% RH to simulate a climate controlled hospital and at 27°C, 80% RH to simulate the environment in West-Africa. Study results found in water EBOV concentration was reduced at a significantly faster rate at 27°C (where it was viable as long as 3 days) than at 21°C  (where it was viable as long as 6 days) (p=0.0001). In human blood, virus concentration was reduced at a significantly faster rate in drying blood (day 5) than in liquid blood (day 8+) for each environmental condition (p<0.0001). No significant difference was found between reduction rates in drying human blood at both environmental conditions. EBOV in blood from experimentally infected non-human primates persisted for a similar duration as EBOV in spiked human blood (Fischer, et al., 2015).

EBOV was also tested on several solid substrates including stainless steel, plastic and polyethylene fabric (used in personal protective equipment). Study results indicate that virus concentration was reduced at a significantly slower rate on all surfaces in controlled hospital setting environments than in tropical conditions. At 21°C, 40% RH virus could be recovered on stainless steel at 8 days, plastic at 11 days, and polyethylene fabric (Tyvek) at 14 days. At 27°C, 80% RH virus recovery on these surfaces was 3 days, 3 days, and 4 days respectively (Fischer, et al., 2015).

Cook et al. (2015) also examined the environmental persistence of the EBOV. Virus was suspended in a simulated organic soil load and dried onto items commonly found in a clinical setting including stainless steel, surgical masks, cotton gown and waterproof plastic gown. This organic soil load was representative of virus shed in a variety of profuse secretions (such as vomit, diarrhea) that would be generated during periods of high viremia. Overall, virus suspended in an organic soil load showed prolonged persistence (192 hours) on some surfaces common to a clinical setting including the surgical mask, plastic gown and steel. The cotton surface showed a 47% reduction after 1 hour exposure, followed by complete inactivation at 24 hours (Cook, et al., 2015).

Sagripanti, Rom, and Holland (2010) examined ZEBOV dried onto solid surfaces to measure the inactivation kinetics of the virus in the dark, on glass substrate, under controlled environmental conditions (corresponding to nighttime inactivation). Results indicated that ZEBOV could not be detected after 5.9 days (Sagripanti, et al., 2010).

Stability in the Clinical Environment

Bausch et al. (2007) tested various acute and convalescent clinical specimens from 26 laboratory-confirmed cases of EVD in a hospital setting in Gulu, Uganda, as well as environmental specimens collected from a hospital isolation ward, for presence of EVD. Only the results of the environmental samples are reported here. The ward routinely followed environmental decontamination procedures as recommended by the World Health Organization (WHO). Two positive environmental samples were used as controls. Of the 33 samples taken, none were culture positive and only the positive control samples had positive RT-PCR results (Bausch, et al., 2007).

More recently, Youkee et al. (2015) used viral swabs to assess EVD contamination within an Ebola Holding Unit in Sierra Leone using RT-PCR for the purposes of testing viral decontamination procedures.  Three sets of swabs were taken at 15 pre-determined locations around the bedside of a positive patient immediately after they left the facility (T0), 30 minutes (T30), and 60 minutes after decontamination (T60). Swab sets 1 and 2 were taken prior to a rapid educational intervention; swab set 3 was taken after a rapid educational intervention to train staff. Prior to decontamination procedures, EVD RNA was detected repeatedly within a limited area around the bedside sites tested (mattress, floor at the middle of the bed, bedframe at the middle of the bed, bed side table, latrine, dirty glove). The mattress was the only item positive at time 0 for each swab set and was visibly contaminated.  In swab sets 1 and 2 (before the rapid educational intervention) at T30 and T60 several sites tested positive for EVD RNA (floor at the head and middle of the bed, bedframe in the middle of the bed and bedside table). In swab set 3 (post rapid educational intervention) there was no EVD RNA detected at T30 or T60. EVD RNA was not detected at any site distant to the bedside (Youkee, et al., 2015).

Conclusion

The studies reported here include several limitations such as differing methodologies, small sample sizes and small sample sets. Potential differences in sampling techniques and sample processing as well as different detection limits of testing assays may also have influenced study results. These limitations may have confounded the results and limit the applicability of findings.

There is some incongruence of results regarding the viability of EVD on various substrates over time among the studies reported here. Although it is understood that different environmental conditions such as temperature and humidity, fluid type(s), and environmental surface characteristics influence the ability of EVD to persist in the environment it is unclear whether positive samples contain replication competent virus and how this relates to transmission potential.

References

Bausch, D. G., Towner, J. S., Dowell, S. F., Kaducu, F., Lukwiya, M., Sanchez, A., Nichol, S. T., Ksiazek, T. G., Rollin, P. E. (2007). Assessment of the risk of ebola virus transmission from bodily fluids and fomites. Journal of Infectious Diseases, 196, (Suppl 2), S142-S147. [OutbreakHelp Star Rating: 4]

Cook, B. W., Cutts, T. A., Nikiforuk, A. M., Poliquin, P. G., Strong, J. E., & Theriault, S. S. (2015). Evaluating environmental persistence and disinfection of the ebola virus makona variant. Viruses7(4), 1975-1986. [OutbreakHelp Star Rating: 5]

Fischer, R., Judson, S., Miazgowicz, K., Bushmaker, T., Prescott, J., & Munster, V. J. (2015). Ebola virus stability on surfaces and in fluids in simulated outbreak environments. Emerging infectious diseases21(7), 1243-1246. [OutbreakHelp Star Rating: 5]

Piercy, T.J., Smither, S.J., Steward, J.A., Eastaugh, L., Lever, M.S. (2010). The survival of filoviruses in liquids, on solid substrates and in a dynamic aerosol. Journal of Applied Microbiology109(5), 1531-1539. [OutbreakHelp Star Rating: 5]

Sagripanti, J.L., Rom, A.M., Holland, L.E. (2010). Persistence in darkness of virulent alphaviruses, Ebola virus, and Lassa virus deposited on solid surfaces. Archives of Virology155(12), 2035-2039. [OutbreakHelp Star Rating: 4.5]

Youkee, D., Brown, C. S., Lilburn, P., Shetty, N., Brooks, T., Simpson, A., Bentley, N., Lado, M., Kamara, T.B., Walker, N.F., Johnson, O. (2015). Assessment of environmental contamination and environmental decontamination practices within an Ebola holding unit, Freetown, Sierra Leone. PLOS ONE10(12), e0145167. [OutbreakHelp Star Rating: 4.5]