Is hypochlorous acid (HOCl) effective in cleaning norovirus from surfaces?

Hypochlorous Acid for Norovirus Surface Disinfection

Hypochlorous acid (HOCl) is effective for cleaning norovirus from surfaces, achieving ≥99.9% (≥3 log10) reduction within 10 minutes at concentrations of 20-200 ppm on both porous and nonporous surfaces. 1

Evidence Quality and Recommendation Basis

The primary evidence comes from a 2007 study demonstrating that HOCl solution effectively inactivates human norovirus and its surrogates on contaminated surfaces, including both liquid application and fogging methods 1. However, the CDC guidelines from 2011 do not specifically mention hypochlorous acid, instead recommending sodium hypochlorite (chlorine bleach) as the gold standard 2.

Practical Application Guidelines

Concentration and Contact Time

• HOCl at 20-200 ppm achieves ≥3 log10 reduction of norovirus within 10 minutes on ceramic tile and stainless steel surfaces 1
• This is significantly lower than the 1,000-5,000 ppm sodium hypochlorite concentration recommended by CDC guidelines 2
• For fogged application in confined spaces, HOCl achieves the same ≥99.9% reduction regardless of surface location or orientation 1

Critical Pre-Cleaning Step

• Always remove visible organic matter (especially fecal material) before applying any disinfectant 2, 3
• Organic loads dramatically reduce the effectiveness of all chlorine-based disinfectants 3, 4
• Even 5,000 ppm sodium hypochlorite cannot completely eliminate norovirus dried in 20% fecal suspension without pre-cleaning 2

Comparative Effectiveness

HOCl vs. Sodium Hypochlorite

While HOCl shows promise at lower concentrations, the CDC guidelines still prioritize sodium hypochlorite because:

• Sodium hypochlorite has well-documented efficacy against human norovirus with decades of use 2
• The evidence for HOCl is based on a single 2007 study using surrogate viruses and RT-PCR detection 1
• Newer research (2022) on chlorous acid water shows superior stability under organic-matter-rich conditions compared to sodium hypochlorite 5

Important Caveat About Surrogate Testing

• Most disinfectant efficacy data relies on surrogate viruses (FCV, MNV, MS2) rather than actual human norovirus 2, 3
• Feline calicivirus (FCV) is not the most resistant surrogate and may overestimate disinfectant effectiveness 2, 3
• RT-PCR detection of viral RNA may not reliably indicate actual viral inactivation 3

Regulatory Considerations

EPA Registration

• In healthcare settings, use only EPA-registered disinfectants with label claims for norovirus 2
• Check if your specific HOCl product is EPA-registered for norovirus (list available at EPA website) 2
• Follow manufacturer's instructions for dilution, application, and contact time 2

Clinical Algorithm for Surface Disinfection

1. Remove gross contamination: Use disposable materials to remove visible fecal matter or vomitus while wearing appropriate PPE 2, 3, 4

2. Pre-clean the surface: Wipe with detergent and water to remove organic load 3, 4

3. Apply disinfectant:

   • If using HOCl: Apply 20-200 ppm solution and allow 10-minute contact time 1
   • If using sodium hypochlorite: Apply 1,000-5,000 ppm (higher end for soiled surfaces) with 4-minute minimum contact time 2

4. Target high-touch surfaces: Focus on bathrooms, door knobs, hand rails, taps, and telephone receivers 2, 4

Common Pitfalls to Avoid

• Do not skip the pre-cleaning step: Detergent cleaning alone fails to eliminate norovirus, and disinfectants are ineffective on heavily soiled surfaces 4
• Do not reuse contaminated cleaning cloths: Cloths can transfer virus to up to seven clean surfaces sequentially 4
• Do not rely on quaternary ammonium compounds or phenolic products: These are less effective against nonenveloped viruses like norovirus 2, 6
• Prepare fresh bleach solutions: Sodium hypochlorite solutions should be prepared within 24 hours or stored at doubled concentration for up to 30 days 2

Bottom Line for Clinical Practice

While hypochlorous acid shows effectiveness against norovirus at lower concentrations than traditional bleach, sodium hypochlorite (1,000-5,000 ppm) remains the CDC-recommended standard due to more extensive documentation of efficacy. 2 If using HOCl, ensure it is EPA-registered for norovirus, apply at appropriate concentrations (20-200 ppm), allow adequate contact time (10 minutes), and always pre-clean surfaces to remove organic matter 1, 3.