In-Clinic Microbiology Comparative Study of Manual Disinfection and the Addition of UV-C Disinfection with Violet AI

Location
India
Industry
Hosptial
Date
July 2025

overview

This study compared manual cleaning alone to manual cleaning plus UV-C disinfection on high-touch surfaces in an operating theater and critical care unit by measuring bacterial colony counts before and after each step. 

Findings indicate using the Violet AI robot after manual cleaning resulted in a greater reduction in microbial contamination than manual cleaning alone. For critical surfaces in high-risk areas, UV-C is not a replacement for manual cleaning but does provide meaningful additional disinfection and improved safety.

Introduction

In high-risk healthcare environments such as operating theaters and critical care units, microbial contamination of surfaces poses an ongoing threat to patient safety. Manual disinfection protocols—although widely used—are susceptible to human error and often fall short in eliminating pathogenic organisms, especially from high-touch and geometrically complex surfaces [1][2]. In some cases, improper manual cleaning may even increase surface contamination, particularly when cloths are reused or cleaning agents are not applied adequately [3].

Ultraviolet-C (UV-C) disinfection has emerged as a supplementary method that can enhance terminal cleaning outcomes. UV-C light disrupts microbial DNA and has shown efficacy across various hospital surfaces, including those difficult to clean thoroughly by hand [4]. A recent systematic review found that UV-C disinfection consistently outperformed manual cleaning, particularly on flat surfaces and in high-risk areas such as isolation rooms and bathrooms [3].

This study compares the effectiveness of manual disinfection versus a combined approach incorporating UV-C light, using percent reduction in microbial contamination on selected high-touch surfaces. It also highlights the risks of non-compliance with SOPs during manual cleaning.

 

Materials and Methods

Study Locations and Sampling

Sampling was conducted in:

  • Cardio & Thoracic Operating Theater (OT)
  • Medical Critical Care Unit (MDCCU)

Fifteen high-touch surfaces were selected for microbial swabbing, including infusion pumps, OT tables, side rails, filter vents, telephones, cardiac tables, and mattress covers.

Sampling Phases

Swabs were collected at three stages:

    1. Pre-Cleaning: Before any cleaning procedures.
    2. Post Manual Cleaning: After standard manual cleaning with hospital-approved disinfectants.
    3. Post UV-C Disinfection: After exposure to UV-C light from one cycle of the Violet Gen4 autonomous robot.

Swabbing was performed using sterile techniques, and samples were cultured on nutrient agar. Colony-forming units (CFUs) were counted after incubation. Fungal growth was also noted when present.

 

Results

The comparative results of microbial load across the three disinfection stages are tabulated below. CFU counts are shown per surface:

Table 1: Surface Contamination Results by Area and Cleaning Phase

Table 2: Percentage Reduction in CFU Count by Area and Cleaning Phase

 

Discussion

Manual disinfection alone led to partial or inconsistent microbial reduction. In some cases, like the infusion pump and filter vent, microbial presence increased post-cleaning, a concerning trend mirrored in existing literature [3][1]. This outcome may result from improper cloth use, insufficient disinfectant application, or failure to follow protocols, potentially contributing to greater contamination and SOP non-compliance [3][2].

In contrast, UV-C disinfection provided reliable, consistent microbial elimination, achieving complete or near-complete reductions in nearly all surfaces tested. This reflects the findings of Boyce et al., who observed significant reductions in CFUs after UV-C intervention [5], and supports broader findings that UV-C yields 92–100% reductions on flat and high-touch surfaces [3].

Notably, fungal growth detected on the door handle was only eliminated following UV-C exposure, highlighting its broad-spectrum efficacy [3].

 

Conclusions and Implications

This comparative analysis confirms that manual disinfection alone is often insufficient, and in some cases counterproductive. Surfaces with irregular geometry or inconsistent cleaning practices are at risk for incomplete decontamination or even increased bioburden [3].

UV-C supplementation:

  • Ensures higher clearance of microbial presence
  • Provides a consistent, operator-independent layer of protection
  • Supports compliance with hospital SOPs and reduces HAI risk [3][7]

Hospitals should consider routine integration of UV-C disinfection in terminal cleaning workflows—especially in critical care zones—to enhance patient safety and minimize infection transmission.

 

References

  1. Carling, P. C., and J. M. Bartley. “Evaluating hygienic cleaning in health care settings: what you do not know can harm your patients.” American Journal of Infection Control, vol. 38, no. 5 Suppl 1, 2010, pp. S41–S50.
  2. Dancer, S. J., and N. A. Simmons. “MRSA behind bars?” Journal of Hospital Infection, vol. 62, no. 3, 2006, pp. 261–263.
  3. Resendiz, Marisol, Dawn Blanchard, and Gordon F. West. “A systematic review of the germicidal effectiveness of ultraviolet disinfection across high-touch surfaces in the immediate patient environment.” Journal of Infection Prevention, vol. 24, no. 4, 2023, pp. 166–177.
  4. Boyce, J. M., and C. J. Donskey. “Understanding ultraviolet light surface decontamination in hospital rooms: A primer.” Infection Control & Hospital Epidemiology, vol. 40, no. 9, 2019, pp. 1030–1035.
  5. Boyce, J. M., N. L. Havill, and B. A. Moore. “Terminal decontamination of patient rooms using an automated mobile UV light unit.” Infection Control & Hospital Epidemiology, vol. 32, no. 8, 2011, pp. 737–742.
  6. Chao Foong, Y., et al. “Mobile phones as a potential vehicle of infection in a hospital setting.” Journal of Occupational and Environmental Hygiene, vol. 12, no. 10, 2015, pp. D232–D235.
  7. Jinadatha, C., et al. “Evaluation of a pulsed-xenon ultraviolet room disinfection device for impact on contamination levels of methicillin-resistant Staphylococcus aureus.” BMC Infectious Diseases, vol. 14, 2014, p. 187.

study by Haystack Microbiology and partner hospital | July 16, 2025

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