2.6 Disinfectant Categories & Selection
Key Takeaways
- Disinfectants are categorized as high-level, intermediate-level, or low-level based on their antimicrobial activity
- EPA registration is required for all hospital disinfectants — check the EPA registration number on the label
- Contact time (kill time) specified on the label MUST be followed — wiping a surface and immediately drying does not disinfect
- Quaternary ammonium compounds (quats) are the most common low-level disinfectants for surface cleaning
- Chlorine compounds (sodium hypochlorite/bleach) are effective intermediate-level disinfectants but corrosive to metals
- Alcohol (70% isopropyl or ethyl) is an intermediate-level disinfectant but evaporates quickly, limiting contact time
- Phenolics are intermediate-level disinfectants with residual activity but should not be used in nurseries
- Never mix disinfectants — chemical reactions can produce toxic fumes or reduce effectiveness
Last updated: March 2026
Disinfectant Categories & Selection
Selecting the correct disinfectant for each application is critical. Using the wrong disinfectant — or using it incorrectly — can leave dangerous pathogens on instruments and surfaces.
Disinfection Levels
| Level | Kills | Does NOT Kill | Used For |
|---|---|---|---|
| High-level | All organisms except high numbers of spores | Large numbers of bacterial spores | Semi-critical items (endoscopes, resp. equipment) |
| Intermediate-level | Vegetative bacteria, most viruses, most fungi, mycobacteria | Bacterial spores | Non-critical items with blood contamination |
| Low-level | Most vegetative bacteria, some viruses, some fungi | Mycobacteria, bacterial spores, some non-enveloped viruses | Non-critical items (surfaces, equipment touching intact skin) |
Common Disinfectant Classes
1. Quaternary Ammonium Compounds (Quats)
- Level: Low-level
- Common use: General surface disinfection, environmental cleaning
- Advantages: Low toxicity, good cleaning ability, pleasant scent, wide availability
- Limitations: NOT effective against mycobacteria, bacterial spores, or many non-enveloped viruses
- Contact time: Varies by product (typically 1-10 minutes — READ THE LABEL)
2. Chlorine Compounds (Sodium Hypochlorite/Bleach)
- Level: Intermediate-level (high-level at higher concentrations)
- Common use: Surface disinfection, blood spill cleanup, C. difficile environmental decontamination
- Advantages: Broad spectrum; effective against C. difficile spores, norovirus, and most pathogens
- Limitations: Corrosive to metals, damages clothing, strong odor, inactivated by organic matter
- Concentration:
- General disinfection: 1:100 dilution (500 ppm)
- Blood spills: 1:10 dilution (5,000 ppm)
- C. difficile: 1:10 dilution (5,000 ppm) or EPA-registered sporicidal product
3. Alcohol (70% Isopropyl or Ethyl)
- Level: Intermediate-level
- Common use: Surface disinfection of small areas, thermometer probes, stethoscopes
- Advantages: Fast acting, no residue, dries quickly
- Limitations: Evaporates quickly (limited contact time), NOT sporicidal, flammable, damages some plastics/rubber
- Key point: Because alcohol evaporates rapidly, achieving the required contact time on surfaces is difficult — it is best for small, clean surfaces
4. Phenolics
- Level: Intermediate-level
- Common use: Environmental surface disinfection (floors, walls, furniture)
- Advantages: Broad spectrum, residual activity (continues working after drying)
- Limitations: Can irritate skin, toxic if absorbed; should NOT be used in newborn nurseries or NICU (can cause hyperbilirubinemia in neonates)
5. Hydrogen Peroxide-Based Surface Disinfectants
- Level: Intermediate to high-level (depending on concentration)
- Common use: Surface disinfection, environmental decontamination
- Advantages: Broad spectrum, good safety profile, environmentally friendly breakdown (water + oxygen)
- Limitations: Some formulations may not be compatible with all surfaces
Critical Rules for Disinfectant Use
Contact Time Is Non-Negotiable
- The contact time (also called wet contact time or dwell time) specified on the product label is the minimum time the surface must remain visibly WET with the disinfectant
- Simply wiping a surface and letting it dry immediately is NOT disinfection
- If the disinfectant dries before the required contact time, reapply
EPA Registration
- All disinfectants used in healthcare must be EPA-registered
- The EPA registration number appears on the product label
- Using a non-registered product for disinfection is a regulatory violation
Concentration
- Dilute exactly as specified — more concentrated is NOT more effective and may be hazardous
- Use manufacturer-provided dispensing systems when available
- Test concentration if manual dilution is performed
Surface Preparation
- Clean before you disinfect — organic matter (blood, soil) inactivates many disinfectants
- A two-step process (clean, then disinfect) or a one-step cleaner-disinfectant can be used
- Heavily soiled surfaces always require cleaning first
Test Your Knowledge
Which disinfectant class should NOT be used in newborn nurseries or NICUs?
A
B
C
D
Test Your Knowledge
The "contact time" on a disinfectant label refers to:
A
B
C
D
Test Your Knowledge
For cleaning up a blood spill on the floor, the recommended sodium hypochlorite (bleach) dilution is:
A
B
C
D