Central Service - Issue 1/2011
Investigations into reproducible cleaning of instruments based on a worst-case model
The efficacy of cleaning surgical instruments was investigated in a multi-centre trial using specially designed gap PCDs and evaluating the reproducible cleaning performance. The PCDs are representative for the the variety found in standard surgical instruments.
The results show that a process with two pre-rinses and 10 minutes holding time yields reliable results, however, the residues found vary widely with shorter process times and for unoiled instruments. The gap width has only minor influence.
Further investigations are in progress on minimally invasive instrumetns and on more complex instrument geometries.
S. Pisot, G. Thumm, P. Heeg, C. Syldatk, K. Roth:
Investigations into the role of the A0 value in the inactivation kinetics of bacteria in thermal disinfection
First, the D values were calculated for several microorganisms at 65, 70 and 75 °C. Test bacteria were selected in terms of their relevance in the medical setting. The following bacterial species were chosen: Pseudomonas (P.) aeruginosa, Staphylococcus (S.) aureus, Enterococcus (E.) faecium and Mycobacterium (M.) terrae. The D values were 0.14 min, 0.12 min and 0.01 min for P. aeruginosa, 0.21 min, 0.13 min and 0.04 min for S. aureus and 1.65 min, 0.35 min and 0.7 min for E. faecium. M. terrae was completely inactivated within a few seconds at 65 °C.
The following investigations were performed for thermal inactivation of the selected bacterium in pure suspension as well as on a metallic surface. The results obtained were compared with the A0 values calculated at different temperatures only for the test organism E. faecium. The metallic discs were contaminated, on the one hand, with the pure bacterial suspension and, on the other hand, with a bacterial-suspension/blood mixture. It was noted that the E. faecium count was reduced more quickly in the suspension test than on the metallic surface. Furthermore, bacteria in the blood mixture proved to be more heat resistant than those in a pure bacterial suspension on a metallic surface.
These tests demonstrated that the A0 value theory described in EN ISO 15883-1 (1) is confirmed in everyday practice.
Reduction of the microbial count of the microorganisms used in these tests at the respective A0 value revealed that an A0 value of 60 is enough to assure effective inactivation of both the bacteria in pure suspension and the bacteria on a metallic surface. Thermal disinfection of medical devices in the hospital setting, which is generally conducted with a process using an A0 value of 600 or 3000, thus offers a high degree of protection to both personnel and patients against infection.
Recommendations by the «Quality Task Group»: Problem instruments when it comes to reprocessing (Part 1)