Regarding chemical disinfectants used in hospital settings, all of the following statements are true EXCEPT:

Explanation

## Chemical Disinfectants in Hospital Practice **Key Point:** Different disinfectants have distinct spectra of activity, penetration capabilities, and limitations. Understanding these differences is essential for selecting the appropriate agent for each clinical scenario. ### Comparison of Common Hospital Disinfectants | Disinfectant | Concentration | Vegetative Bacteria | Spores | Viruses | Organic Matter Sensitivity | Key Limitation | |--------------|----------------|-------------------|--------|---------|---------------------------|----------------| | **Glutaraldehyde** | 2% | ✓✓✓ | ✓✓✓ | ✓✓ | Moderate | Toxic vapours; slow sporicidal action | | **Alcohols (70%)** | 70% | ✓✓✓ | ✗ | ✓✓ | **Poor** (rapid evaporation) | Non-sporicidal; poor penetration | | **Chlorine (0.5–1%)** | 0.5–1% | ✓✓✓ | ✓ | ✓✓✓ | **Very poor** (inactivated by protein) | Corrosive; unstable solutions | | **QACs** | 0.1–1% | ✓✓ | ✗ | ✓ | **Poor** (biofilm resistance) | Non-sporicidal; poor biofilm penetration | **High-Yield:** Quaternary ammonium compounds (benzalkonium chloride, cetylpyridinium chloride) are **cationic surfactants** that are **NOT sporicidal** and are **ineffective against biofilms** — they are actually inactivated by organic matter and biofilm matrices. They are suitable only for routine surface disinfection of lightly contaminated areas. ### Why Option 3 is Incorrect QACs are **inferior** to alcohols for heavily contaminated surfaces because: 1. **No sporicidal activity** — cannot kill spores 2. **Poor biofilm penetration** — biofilms are negatively charged and repel cationic QACs 3. **Inactivated by organic matter** — proteins and lipids reduce efficacy 4. **Lower microbicidal speed** — slower than alcohols on vegetative cells Alcohols, while also non-sporicidal, are **faster-acting** on vegetative bacteria and viruses, making them preferable for contaminated surfaces despite their own limitations. **Mnemonic:** **QAC = Quick At Clean surfaces** — quaternary ammonium compounds work best on clean, lightly soiled surfaces; they fail on heavily contaminated or biofilm-laden materials. **Clinical Pearl:** In operating theatres, glutaraldehyde (high-level disinfectant) or peracetic acid is chosen for endoscopes; chlorine is used for blood spills; alcohols for skin antisepsis. QACs are relegated to routine housekeeping disinfection only. [cite:Prescott's Microbiology Ch 7; CDC Guidelines on Disinfection and Sterilisation]