Using QAC disinfectant in hospital operating theatres

The disinfection process with QAC has been considered suitable for use in common rooms.

Based on “Evaluation of an Automatic Fogging Disinfection Unit”
Study conducted by Nakata et al., Environ. Health Prev. Med., 2001 (6), 160-4.

Contaminated surfaces in our living environment are contributing to the spread of communicable diseases. Regular disinfection in public areas is vital to lowering pathogenic loading and protecting public health. Disinfection efficacies are subjected to a number of variables, including the choice of active ingredient, formulation, concentration, administration methods (i.e. spray, wipe, etc) and other environmental variables (i.e. %RH, temperature, etc).

This White Paper highlights a case study based on real-life disinfection using an automatic fogging unit within hospital operating theatres.

Study Design:

Operating theatres (108 – 217 m3) were subjected to disinfection by the following disinfectants:
  1. 0.2% sodium hypochlorite (NaClO, commonly known as bleach)
  2. Acidic electrolytic water (active component = hypochlorous acid (HOCl))
  3. 0.5% glutaraldehyde (formaldehyde-based disinfectant)
  4. 0.2% benzalkonium chloride (commonly known as Quaternary Ammonium Compounds (QAC))

Before disinfection, ventilation system within the operating theatre was switched off. Disinfection was performed via stationary automatic fogging disinfection unit, which generated even spray particles of approximately 10 µm. The volume of disinfectant used was set in the range of 30-50 mL/m3. After disinfection, the operating theatres were left as they were for 15 minutes before restarting ventilation to further precipitate the disinfectants from the air.

Results and Summary:

Bactericidal effect against Bacillus and S. aureus was examined for each of the tested disinfectants. Taking into account all sample points within the operating theatre (wall, floor and others1), 0.2% benzalkonium chloride, 0.2% sodium hypochlorite and 0.5% glutaral all achieved >90% reduction against both bacterial strain (please see Table below). More impressively, 100% reduction against Bacillus was achieved for all floor sampling locations when using 0.2% benzalkonium chloride, highlighting its superior disinfection efficacy. In contrast, acidic electrolytic water only managed 77% and 89% reduction for Bacillus and S. aureus, respectively.


Average reduction rate (%) of CFU


S. aureus

0.2% Sodium hypochlorite



Acidic electrolytic water



0.2% Benzalkonium chloride



0.5% Glutaraldehyde



Note 1: Each operating theatre contains 40-50 sampling points, ranging from floor, wall, operating table, surgical lights, doorknob, power-outlet sockets, shelf and ceilings.

The disinfection process with QAC has been considered suitable for use in common rooms. Based on the authors’ observations, QACs was found to have the least adverse effect on medical instruments, and that fog spray can reach comparatively narrow gaps and disinfect the entire floor within the operating theatre.

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