Inactivation of Microorganisms in the Complex Regions of Transvaginal Ultrasound Probes By a UVC-LED Light Based Disinfection System

This study demonstrates that a novel UVC-LED disinfection system effectively achieves 100% decontamination of complex transvaginal ultrasound probe surfaces, including difficult-to-reach areas, by eliminating diverse clinical microorganisms and achieving a >6.7 log10 reduction of Bacillus subtilis spores within 90 seconds.

The Gist

The Big Picture: The "Dirty Secret" of Medical Probes

Imagine a doctor using a special wand (an ultrasound probe) to look inside a patient's body. This wand is like a high-tech detective that needs to be incredibly clean to avoid passing germs from one patient to another.

The problem? These wands aren't smooth like a pool cue. They have tiny nooks, crannies, grooves, and weird bends (like the handle or the lens area). Think of these complex shapes like a Swiss Army knife or a coral reef. Germs love to hide in these little "caves" where regular cleaning sprays or wipes can't reach. This study asked: Can we actually clean these hidden spots, or do the germs stay safe in their little fortresses?

The Experiment: The "90-Second Sunlight"

The researchers tested a new cleaning machine that uses UV-C LED light.

• The Analogy: Imagine the sun's rays are so strong they can zap germs, but you can't stand outside in the sun for 90 seconds without getting burned. This machine is like a super-powered, focused tanning bed for germs, but instead of giving them a tan, it destroys them instantly.
• The Setup: They took real probes used in a fertility clinic. Before cleaning, they swabbed the "caves" (notches, handles, grooves) to see what was hiding there.
• The Treatment: They put the probes into the UV-C machine for just 90 seconds.

What They Found: The "Before" and "After"

1. The "Before" Picture (The Messy Room)
Before the UV light, the probes were surprisingly dirty.

• The Germs: They found a whole zoo of bacteria, including Staphylococcus (common skin germs), Pseudomonas (often found in water), and even Bacillus (which forms tough, armor-like spores).
• The Hiding Spots: The "caves" were full. Some spots had up to 3.9 log₁₀ CFU of bacteria.
  • Simple Math: In plain English, this means there were roughly 8,000 germs in a tiny spot on the handle.
• The Covers: Even the plastic covers put on the probes to protect them were dirty! This is like putting a clean raincoat on a muddy dog; the raincoat gets dirty too.

2. The "After" Picture (The Clean Slate)
After the 90-second UV treatment:

• The Result: Zero germs. Not one.
• The Magic: The UV light managed to reach into the "caves" and "corners" where the germs were hiding. It was like shining a flashlight into every single crack of a dark cave and finding that every monster was gone.
• The Tough Test: To be sure, they also smeared the probes with Bacillus spores (the "super-villains" of the germ world that are very hard to kill). The UV light killed 99.9999% of them.

Why This Matters: The "Hidden Danger"

Usually, hospitals use chemical sprays or soaking baths to clean these probes. But imagine trying to clean a garden hose with a kink in it using a spray bottle. The water (or cleaner) might hit the outside, but it can't get into the kink where the dirt is stuck.

• The Old Way: Chemicals often miss the "cold spots" (the areas where light or liquid can't easily reach).
• The New Way: The UV-C light is like a 360-degree spotlight. It doesn't matter if the probe has a bend or a groove; the light bounces around and hits every surface, zapping the germs instantly.

The Takeaway

This study proves that:

1. Medical probes get very dirty in their hidden corners, even when doctors are careful.
2. Standard cleaning might miss the germs hiding in those complex shapes.
3. UV-C LED light is a superhero for cleaning. In just 90 seconds, it can wipe out 100% of the bacteria, even the tough ones hiding in the deepest cracks.

In short: This new machine is like a "magic eraser" that ensures the medical tools are truly sterile, keeping patients safe from infections that could sneak through the cracks.

Technical Summary

1. Problem Statement

Transvaginal ultrasound (TVUS) probes are critical diagnostic tools that frequently contact mucous membranes and non-intact skin, posing significant risks for cross-contamination and nosocomial infections.

• Structural Vulnerability: Probes possess complex geometries (notches, grooves, seams, bent areas, and textured handles) that act as "cold spots" where light and cleaning agents struggle to reach. These areas retain biological material and microorganisms even after standard cleaning.
• Limitations of Current Methods: Conventional high-level disinfection (HLD) methods often fail to penetrate these recessed areas effectively. Furthermore, probe covers (sheaths) are not foolproof; they can tear or leak (reported rates up to 81% for commercial covers), allowing direct contact between body fluids and the probe surface.
• Pathogen Risk: Contaminated probes can transmit a wide range of pathogens, including bacteria (Staphylococcus, Pseudomonas, Bacillus, Legionella), viruses (HPV, HIV, CMV), and fungi, posing severe risks to patients, particularly pregnant women.

2. Methodology

The study employed a dual-approach strategy combining ex vivo clinical sampling and in vitro challenge testing to evaluate a novel UVC-LED HLD system (Lumicare ONE).

A. Ex Vivo Clinical Sampling

• Source: Two TVUS probes were sampled from an IVF clinic in Sydney, Australia, after clinical use but before disinfection.
• Sampling Sites: Specific "high-risk" complex regions were targeted:
  • Probe A: Top notch, bottom notch, left handle, right handle.
  • Probe B: Lens, edges, and bent groove regions.
• Process: Sterile swabs were used to sample pre-disinfection sites. Probes were then treated with the UVC-LED system for 90 seconds. Post-treatment swabs were taken from the opposite side of the same sites.
• Sheath Analysis: Five used probe covers were also swabbed internally to assess barrier integrity.
• Environmental Monitoring: Agar plates were exposed in both the clinical examination room and the disinfection room to map background environmental contamination.
• Identification: Microorganisms were cultured on Chocolate Blood Agar (CBA) and Sabouraud's Dextrose Agar (SDA) under aerobic, microaerophilic, and anaerobic conditions. Isolates were identified using MALDI-TOF mass spectrometry.

B. In Vitro Challenge Testing (Robustness Assessment)

• Sterilization: Probes were pre-sterilized with 4% bleach to ensure a baseline of zero contamination.
• Inoculation: Probes were inoculated with Bacillus subtilis spores (ATCC 19659), a highly resistant spore-forming bacterium used as a surrogate for difficult-to-kill pathogens.
• Treatment: Spores were dried on complex sites (notches, bends, lenses) and exposed to the UVC-LED system for 90 seconds.
• Quantification: Viable spore counts were recovered via swabbing, serial dilution, and plating on Tryptic Soy Agar (TSA) to calculate Log₁₀ reductions.

3. Key Contributions

• Focus on "Cold Spots": Unlike previous studies that tested general probe surfaces, this research specifically targeted the most difficult-to-clean geometric features (notches, grooves, and bent edges) where microbial retention is highest.
• Comprehensive Microbial Profiling: The study utilized MALDI-TOF to identify a diverse spectrum of clinical and environmental pathogens, including multi-drug resistant strains and spore-formers, found on used probes.
• Validation of UVC-LED Efficacy on Spores: By using Bacillus subtilis spores, the study demonstrated the system's ability to achieve high-level disinfection standards against organisms known for extreme resistance to chemical disinfectants.
• Environmental Correlation: The study linked probe contamination directly to the environmental microbiome of the clinical and disinfection rooms, highlighting the role of handling and air currents in re-contamination.

4. Key Results

A. Ex Vivo Findings (Clinical Probes)

• Pre-Treatment Contamination:
  • Contamination rates ranged from 25% to 57% across different sites.
  • Microbial loads reached up to 3.9 log₁₀ CFU.
  • Identified Pathogens: Staphylococcus epidermidis (most prevalent), Pseudomonas koreensis, Bacillus cereus, Propionibacterium spp., Legionella pneumophila, and Tsukamurella spp.
  • Sheath Contamination: 4 out of 5 sheaths were contaminated, with S. epidermidis reaching 4.3 log₁₀ CFU, indicating frequent barrier failure.
• Post-Treatment Efficacy:
  • After 90 seconds of UVC exposure, 0% contamination was detected on any sampled site.
  • 100% decontamination was achieved across all complex regions (notches, handles, grooves, lenses).

B. In Vitro Findings (Spore Challenge)

• Log Reduction: The UVC system achieved a reduction of >6.7 log₁₀ CFU for Bacillus subtilis spores across all tested regions (handles, notches, lenses, bent edges).
• Residual Counts: Post-treatment viable counts were negligible (0.00 to 0.20 log₁₀ CFU), effectively meeting high-level disinfection standards.

C. Environmental Findings

• Both clinical and disinfection rooms showed persistent background contamination.
• The clinical room generally had higher microbial loads than the disinfection room.
• The microbial profile on the probes closely mirrored the environmental flora, suggesting transmission via handling and air currents.

5. Significance and Conclusion

• Clinical Impact: The study provides robust evidence that UVC-LED technology can effectively disinfect the "complex regions" of TVUS probes that are typically missed by manual cleaning or chemical HLD.
• Speed and Reliability: The system achieved complete inactivation in just 90 seconds, offering a rapid, reliable, and consistent alternative to time-consuming traditional methods.
• Safety: By eliminating resistant spores and diverse bacterial pathogens from recessed areas, the system significantly reduces the risk of cross-contamination and nosocomial infections in fertility and gynecological clinics.
• Limitations: The study did not evaluate viral inactivation (though bacterial efficacy suggests potential) and did not directly model transmission dynamics, though environmental monitoring provided strong indirect evidence.

Conclusion: The UVC-LED disinfection system, utilizing UVMESH technology for 360° coverage, is a highly effective solution for high-level disinfection of complex medical devices, ensuring patient safety by eliminating microbial reservoirs in hard-to-reach probe geometries.