AOAC Use-Dilution Test for Disinfectants
Q.01
What is the AOAC use-dilution test for disinfectants, how does EPA use it for registration and in the Antimicrobial Testing Program, what are the performance criteria, and what happens when a registered hospital disinfectant fails?
A.01
The AOAC use-dilution method (UDM) is a carrier test for liquid disinfectants on hard surfaces. Carriers are inoculated with a test organism, dried, exposed to the product at its label use-dilution, and then cultured for survivors. EPA relies on it in two places. Before registration, it is the core efficacy data behind a hospital disinfectant claim under 40 CFR 158.2220 and test guideline 810.2200. After registration, EPA's Antimicrobial Testing Program (ATP) bought marketed products and re-tested them. A product passes only if no more than 1 of 60 carriers shows growth. When a registered product fails, EPA contacts the registrant and the enforcement office. The outcome can be removal of the claim from the label, voluntary cancellation, or a stop sale order.
Approach: I used the current 40 CFR Part 158 text (eCFR snapshot of 28 Sept 2026) and the ATP product status list (EPA's March 2018 list). Method details and what happens after a failure come from epa.gov search snippets, not full documents.
1. What the test is
- Methods: AOAC UDM 955.15 for Staphylococcus aureus and 964.02 for Pseudomonas aeruginosa (EPA UDM performance standard revision document).
- EPA's own SOP, MB-05: it covers P. aeruginosa (ATCC 15442), S. aureus (ATCC 6538) and Salmonella enterica (ATCC 10708) on hard surfaces (MB-05-16).
- Carriers: about 80 are inoculated. 60 are tested, 6 are used for inoculum counts and 1 is a viability control.
- Inoculum: the mean log density per carrier must be between 6.0 and 7.0 (10⁶ to 10⁷ CFU). The current version is MB-05-17.
- Revisions: EPA re-analysed the method's variability and the basis of its performance standard. It sent three manuscripts to the Journal of AOAC International to support revising the AOAC methods (revision document).
2. How EPA uses it at registration
- Legal basis: under 40 CFR 158.2220(a)(2), every product with a public health claim (defined in §158.2204(a)) must be supported by product performance data. Those data must be submitted with any application for registration or amended registration [1].
- Applicable guideline: for hard-surface disinfectants the requirement row is OCSPP 810.2200, "Disinfectants for Use on Hard Surfaces: Efficacy Data Recommendations". It is Required for all use patterns, and the end-use product is the test substance [1].
- Related guidelines: separate rows cover sterilants (810.2100), hard-surface sanitizers (810.2300), fabrics and textiles (810.2400), air sanitizers (810.2500) and disinfectants for use in water (810.2600) [2][3][4].
- Products without a public health claim: registrants must still make sure through testing that the product works. EPA can ask for data case by case [1].
- Hospital claim: the product must pass the UDM against both S. aureus and P. aeruginosa (revision document). A tuberculocidal claim also needs efficacy against Mycobacterium bovis BCG (EPA ATP page).
3. Performance criteria
- Pass: 0 or 1 positive carriers out of 60, for each of S. aureus, P. aeruginosa and S. enterica (MB-05-16).
- Valid test: the carrier inoculum must fall within log 6.0 to 7.0. If it doesn't, the run doesn't count.
- The snippets I found don't give the number of product lots or the contact time, so I don't state them here.
4. The Antimicrobial Testing Program
- Purpose: to check that EPA-approved hospital disinfectants and tuberculocides on the market still meet the efficacy standards. EPA obtained registered sterilants, disinfectants and tuberculocides from manufacturers, distributors and sellers and tested them with the standard methods (ATP page).
- Status list: EPA's March 2018 list has 546 products, one row per registration number:
| ATP status | Products |
|---|---|
| Agency Confirmed Efficacy | 258 |
| No Post-Market Testing By EPA | 264 |
| Agency Taking Action | 24 |
- Earlier failure rates: EPA's Office of Inspector General reported in 2009 that efficacy testing in 2005-2006 showed a 40% failure rate for tuberculocidal products and 29.5% for hospital disinfectants (OIG hotline report 09-P-0152).
5. When a registered hospital disinfectant fails
- Notification: program procedures require EPA's Office of Pesticide Programs to tell both the registrant and the Office of Enforcement and Compliance Assurance (OIG report).
- Outcome: EPA decides the next step (ATP page). The options are:
- removal of the hospital disinfectant or tuberculocidal claims from the label;
- voluntary cancellation of the registration by the manufacturer; or
- removal from the market through stop sale orders issued by EPA.
- "Agency Taking Action" status: this covers products still being tested or reviewed, and products facing regulatory or enforcement action.
- The 24 products in this status in March 2018:
| EPA Reg. No. | Product | Registrant |
|---|---|---|
| 875-106 | RENDER II | Diversey, Inc. [5] |
| 8296-1 | MAR-V-CIDE | Marvy William Company [6] |
| 8155-5 | General Purpose/Non-Acid Husky G/P Disinfectant Cleaner | Canberra Corporation [7] |
| 70467-3 | BioSURF | Micrylium Laboratories [8] |
| 66171-2 | Advantage 128 | Preserve International [9] |
| 66171-1 | Advantage 256 Cleaner Disinfectant Deodorant | Preserve International [10] |
| 63838-1 | Perasan 'A' | Enviro Tech Chemical Services [11] |
| 61178-1 | D-125 | Microgen, Inc. [12] |
| 60142-3 | Virahol Hospital Surface Disinfectant Towelette | Veridien Corporation [13] |
| 60142-1 | Virahol | Veridien Corporation [14] |
| 59894-10 | KwikKill Disinfectant Deodorizing Cleaning Wipes | M & S Research [15] |
| 5813-1 | Clorox Bleach | The Clorox Co. [16] |
| 5736-102 | Super-Bol | Diversey, Inc. [17] |
| 52252-7 | Actril Cold Sterilant | Medivators Inc. [18] |
| 46851-10 | ProSpray Wipes Disinfectant Towelettes | Certol International [19] |
| 46597-2 | Q-San | Chemstar Corp. [20] |
| 3862-178 | Tek-Phene | ABC Compounding Co. [21] |
| 3862-177 | Tek-Trol Disinfectant Cleaner Concentrate | ABC Compounding Co. [22] |
| 3862-112 | Chemscope Pine Kleen Tek-Trol Disinfectant | ABC Compounding Co. [23] |
| 34810-35 | Clean-Cide | Wexford Labs [24] |
| 1839-93 | Powder Detergent/Disinfectant | Stepan Company [25] |
| 1839-174 | Stepan Towelette | Stepan Company [26] |
| 11694-34 | Do-It All | ITW Professional Brands [27] |
| 10324-56 | Maquat 256 | Mason Chemical Co. [28] |
Being in this status does not by itself mean the product failed. It also covers products still under testing or review, and the list doesn't say which applies to each product.
I can check the current registration status of any of these 24 products next if that would help.
Sources:
Q.02
INDEX
[1]158.2220 table 0 row 1EPA[2]158.2220 table 0 row 0EPA[3]158.2220 table 0 row 2EPA[4]158.2220 table 0 row 5EPA[5]RENDER IIEPA[6]MAR-V-CIDEEPA[7]GENERAL PURPOSE/NON- ACID HUSKY G/P DISINFECTANT CLEANEREPA[8]BioSURFEPA[9]ADVANTAGE 128EPA[10]ADVANTAGE 256 CLEANER DISINFECTANT DEODORANTEPA[11]PERASAN 'A'EPA[12]D-125EPA[13]VIRAHOL HOSPITAL SURFACE DISINFECTANT TOWELETTEEPA[14]VIRAHOLEPA[15]KWIKKILL DISINFECTANT DEODORIZING CLEANING WIPESEPA[16]CLOROX BLEACHEPA[17]SUPER-BOLEPA[18]ACTRIL COLD STERILANTEPA[19]PROSPRAY TM WIPES, DISINFECTANT TOWELETTESEPA[20]Q-SANEPA[21]TEK-PHENEEPA[22]TEK-TROL DISINFECTANT CLEANER CONCENTRATEEPA[23]CHEMSCOPE PINE KLEEN TEK-TROL DISINFECTANTEPA[24]CLEAN-CIDEEPA[25]POWDER DETERGENT/DISINFECTANTEPA[26]STEPAN TOWELETTEEPA[27]DO-IT ALLEPA[28]MAQUAT 256EPA
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