3.2.1. Efficacy of Four Disinfectants against EBOV-Ecran on Aluminium Coupons
For the aluminium coupons, under the parameters tested, the mean titre of EBOV-Ecran recovered from the coupon was ~1.5 × 105 TCID50/mL. Addition of sodium hypochlorite or Ardrox 6092 resulted in no detectable virus in the TCID50 assay (). There was also no detectable EBOV-Ecran when Ardrox 6092 and sodium hypochlorite were added to virus on a sterile cell culture plate (no coupon; ). When Calla 1452 was added to EBOV-Ecran on aluminium coupons 7 × 102 TCID50/mL of EBOV-Ecran was recovered from the sample and when Calla 1452 and EBOV-Ecran were mixed on a sterile cell culture plate, viable virus was also seen (). Low levels of EBOV-Ecran were detected when Desintex was added to aluminium coupons and viable virus was also observed, albeit below the LoQ of the assay, when Desintex and EBOV-Ecran were tested on a sterile cell culture plate only ().
For the aluminium coupons, a greater than 4-log10 drop in EBOV-Ecran titre was observed with Ardrox 6092 and sodium hypochlorite (). Based on mean counts, a 4-log10 drop in EBOV-Ecran titre was also observed with Desintex on aluminium, although viable virus was recovered (). When no coupon was present, a 4-log10 drop in EBOV-Ecran titre was observed for all four disinfectants ().
3.2.2. Efficacy of Four Disinfectants against EBOV-Ecran on Strapping Coupons
Poor recovery was observed for pilot strapping (), with a mean titre of 2 × 103 TCID50/mL. A 4-log10 reduction in titre therefore fell below the LoQ of the assay. Samples were still processed in the TCID50 assay despite the inability to observe the necessary reduction in order to identify a degree of activity prior to serial cell passage. As with the aluminium coupons, no viable virus could be detected on strapping coupons treated with Ardrox 6092 or sodium hypochlorite in the TCID50 assay (). When Calla 1452 was added to EBOV-Ecran on strapping, 2.3 × 102 TCID50/mL of EBOV-Ecran was recovered and when Desintex and EBOV-Ecran were tested on strapping coupons no viable virus was detected (). The use of TCM in place of EBOV-Ecran as a negative control was conclusive for all samples types as no viable virus was detected (results not shown). Due to poor recovery, a 4-log10 reduction in titre was not achieved with any disinfectant on the strapping coupons ().
Additional qualitative testing of disinfectants on strapping coupons was performed by serial passage. All samples from strapping coupons treated with disinfectant or media only were subject to three passages in cells to allow for amplification of low numbers of viable virus to detectable limits. After three passages, no viable virus was observed in replicate Ardrox 6092- or sodium hypochlorite-treated samples suggesting there had been complete inactivation of EBOV-Ecran on the strapping coupons when treated with these disinfectants. Desintex-treated strapping coupons were also all negative for viable virus after three passages, with the exception of one of the Desintex-treated EBOV-Ecran samples from a sterile cell culture plate (no coupon) after the second passage. This suggests that this concentration of Desintex does not consistently provide complete inactivation. Calla 1452-treated samples were positive for viable virus after the first passage (when recovered from strapping coupons and after the second passage when recovered from a sterile cell culture plate (no coupon).
Two-way ANOVA analysis with Bonferroni’s multiple comparison test indicated that the difference in log reduction for each disinfectant compared to the log reduction with no disinfectant (TCM only, 0, no reduction) was significant for Ardrox 6092, sodium hypochlorite and Desintex on all three surface types (p≤ 0.01 for aluminium and for when no coupon was used and p ≤ 0.05 for strapping). Calla 1452 produced a significant log reduction from control only when no coupon was present (p ≤ 0.01). For each disinfectant, there was no significant difference in log reduction between the three different surface types.