Scoping review on the efficacy of filter and germicidal technologies for capture and inactivation of micro-organisms and viruses.

The COVID-19 (SARS-CoV-2) pandemic increased the focus on preventing contamination with airborne pathogens (e.g. viruses, bacteria, and fungi) by reducing their concentration. Filtration, UV or ionization technologies could contribute to air purification of the indoor environment and inactivation of micro-organisms. The aim of this study was to identify the relevant literature and review the scientific evidence presented on the efficacy of filter and germicidal technologies (e.g. non-physical technologies) in air purification applications used to capture and inactivate micro-organisms and airborne viruses (e.g. SARS-CoV-2, rhinovirus, influenzavirus) in practice. A scoping review was performed to collect literature. Adopting exclusion criteria resulted in a final number of 75 studies to be included in this research. Discussion is presented on inactivation efficiencies of ultraviolet germicidal irradiation (UVGI) and ionization applications in laboratory studies and in practice. Specific attention is given to studies relating the use of UVGI and ionization to inactivation of the SARS-CoV-2 virus. Based on the consulted literature, no unambiguous conclusions can be drawn regarding the effectiveness of air purification technologies in practice. The documented and well-controlled laboratory studies do not adequately represent the practical situation in which the purifier systems are used.

Design variables with significant effect on system performance of unidirectional displacement airflow systems in hospitals.

BACKGROUND: The effectiveness of an airflow system in preventing entrainment of particles carrying micro-organisms from the periphery of an operating room (OR) or instrument lay-up room (ILR) is affected by many variables. It is suspected that differences in the design of the systems affect the effective protection ratio (EPR): the ratio of the size of the protected area to the surface area of the supply canopy. However, no analysis has yet been done to determine which design variables have a significant effect on this ratio. AIM: To evaluate which design variables have a significant effect on the performance of airflow systems (EPR) in ORs and ILRs. METHODS: All general and teaching hospitals in the Netherlands (N = 77) were asked to provide data from their standardized (at-rest measurement method) compulsory systems assessment reports for ORs and ILRs. Nineteen hospitals (25%) with a total of 22 hospital sites supplied information of sufficient completeness and homogeneity, resulting in measurement data for 101 ORs and 23 ILRs. This dataset was analysed using Statistical Package for Social Sciences. FINDINGS: For ORs, important predictors for the EPR were: shape of the canopy; air speed under the supply canopy; height of the canopy screen; type of system; and size of the canopy. These significant predictors (P < 0.05) explain 48% of the outcome in the dataset. For ILRs, significant predictors for the EPR were: the position of exhaust air terminals; height of the canopy screen; and size of the canopy. These significant predictors explain 66% of the outcome in the dataset. CONCLUSION: On the basis of the dataset available for analysis, it is concluded that the ratio of the size of the protected area to the surface area of the supply canopy (EPR) improves with the presence and the height of a screen around the canopy, the surface area of the supply canopy, and the air speed of the supply air under the canopy. This information can be used as guidance for the future design of unidirectional displacement airflow systems.

Effect of using ceiling-mounted systems for imaging in hybrid operating rooms on the level of colony-forming units during surgery.

BACKGROUND: Large imaging systems in hybrid operating rooms are used increasingly. However, the effect of these ceiling-mounted imaging systems on air quality during surgical procedures has not been studied to date. AIM: To evaluate the level of colony-forming units (cfu)/m3 near the surgical wound and near the instrument table during surgery. METHODS: Measurements were performed in four hybrid operating rooms at four different hospitals. During surgical procedures, at least three samples were taken with active slit air samplers. At the end of the day's surgical schedule, simulations involving movement of the ceiling-mounted system were also performed. The threshold value for the average cfu level during a surgical procedure was set at ≤10 cfu/m3, and for individual samples was set at ≤30 cfu/m3. RESULTS: The median value near the surgical wound was 1 cfu/m3 and at the instrument table was 2 cfu/m3. However, in one hybrid operating room (two procedures out of 16) where the instrument table was not positioned directly under the unidirectional flow (UDF) system, the threshold value for the average cfu level at the instrument table was exceeded. For one of these procedures, the maximum value for an individual sample was also exceeded. CONCLUSIONS: A ceiling-mounted imaging system in combination with a UDF system can result in cfu levels near the surgical wound and at the instrument table that are well below the threshold value of 10 cfu/m3 during surgery. If the instrument table is not positioned directly under the UDF system, the cfu level is higher.

The Effect of Operating Lamps on the Protected Area of a Unidirectional Down Flow (UDF) System.

BACKGROUND: Operating lamps are often seen as the most disruptive factors within the protective area in the operating theater (OT). The effect of the operation lamps (with different shapes) should be demonstrated in an OT by trial, since research on the effects of the lamps is still limited. OBJECTIVES: The main aim of this study was to determine the effects of a skirt, different lamps, and the position of the lamp on the protected area. METHODS: The concentration of airborne particles was measured under different circumstances, in order to determine the size and quality of the protected area. This entrainment/segregation test is based on the deliberate and controlled emission of particles outside the zone that is protected. FINDINGS AND CONCLUSIONS: The degree of protection (DP) at the center of the protected area was higher for the case with the skirt. This skirt stimulates more down flow and prevents the early entry of particles into the protected area. It can also be concluded that Lamp Y, due to its open shape, has the most positive effect on the DP at the center. It has also been shown that the position of the lamp has an effect on the protected area.

Effect of switching off unidirectional downflow systems of operating theaters during prolonged inactivity on the period before the operating theater can safely be used.

BACKGROUND: Switching off air handling systems in operating theaters during periods of prolonged inactivity (eg, nights, weekends) can produce a substantial reduction of energy expenditure. However, little evidence is available regarding the effect of switching off the air handling system during periods of prolonged inactivity on the air quality in operating theaters during operational periods. The aim of this study is to determine the amount of time needed after restarting the ventilation system to return to a stable situation, with air quality at least equal to the situation before switching off the system. METHODS: Measurements were performed in 3 operating theaters, all of them equipped with a unidirectional downflow (UDF) system. Measurements (particle counts of emitted particles with a particle size ≥0.5 µm) were taken during the start-up of the ventilation system to determine when prespecified degrees of protection were achieved. Temperature readings were taken to determine when a stable temperature difference between the periphery and the protected area was reached, signifying achievement of a stable condition. RESULTS: After starting up the system, the protected area achieved the required degrees of protection within 20 minutes (95% upper confidence limit). A stable temperature difference was achieved within 23 minutes (95% upper confidence limit). Both findings lie well within the period of 25 minutes normally required for preparations before the start of surgical procedures. CONCLUSIONS: Switching off the ventilation system during prolonged inactivity (during the night and weekend) has no negative effect on the air quality in UDF operating theaters during normal operational hours.

Laying-up of sterile instruments in the operating theatre: equal or superior protection by using a horizontal unidirectional air flow system.

BACKGROUND: A system for the preparation of sterilized instruments with unidirectional horizontal air flow (UDHF) has several advantages over a unidirectional down flow system (UDDF). The advantages are based on the installation of the system being more flexible and easier to use, no cooling of the air flow being necessary and less air being needed for circulation, resulting in reduced energy use. OBJECTIVES: The objective of this study was to determine whether a system with UDHF performs equal or superior to a system with UDDF in terms of prevention of contamination of the air (the presence of particles and micro-organisms) during the laying-up process. METHODS: The degree of protection (DP) offered by two UDHF system variants and two UDDF system variants was determined for several static set-ups and a dynamic simulation of the process. In addition to determining the level of protection for several categories of particle size, colony-forming units (CFU) were also measured during process simulations. FINDINGS: When maximum protection (no particles present) is considered, the UDHF systems performed significantly better than the UDDF systems for particles ≥2.5µm. When particles were present, there was no significant difference between systems for particles ≥0.3 and ≥0.5µm. However, the performance of the UDHF system was superior to that of the UDDF system (DP) for particles ≥1.0µm representing the bacteria-carrying particles. During the process measurements, no CFU were found with the UDDF system in 64% of the measurements, compared with 90% for the UDHF system (P = 0.012). CONCLUSIONS: The UDHF system offers equal or superior protection to the UDDF system against contamination of the clean area within which the laying up takes place. Despite our finding that the differences did not always reach statistical significance (due to low background concentrations), there is a clear trend, from the small-sized particles (≥1.0µm) up to the largest sizes considered, including bacteria-carrying particles, that demonstrates the superiority of the horizontal flow system. The UDHF system offers a more robust solution than the UDDF system, provided that good work instructions are given and the height of the table and height of the plenum are properly adjusted.