Infection Control · patient case question
Which agent is best suited to disinfecting hard, smooth environmental surfaces such as countertops?
Patient case: Infection control and a poor panoramic film
Patient: Practice-based scenarios
Chief Complaint: Not applicable.
Background: A surgical extraction is scheduled and the patient's adult daughter asks to remain in the operatory to support her. A separate patient on the list has ACTIVE pulmonary tuberculosis and needs urgent care. Environmental surfaces are being reviewed after an inspection.
Findings: A panoramic radiograph taken earlier in the day shows a broad dark radiolucent band running across the apices of all the maxillary teeth, obscuring the region of interest. The patient was positioned correctly in the horizontal and vertical planes and the spine is straight.
Show answer and explanation
Correct answer: D. A phenolic compound
- A. ALCOHOL is a poor SURFACE disinfectant for three reasons: it evaporates too quickly to maintain the required contact time, it FIXES organic debris rather than penetrating it, and it degrades plastics and vinyl with repeated use. It is acceptable for small immersible items, not for operatory surfaces.
- B. Quaternary ammonium compounds are LOW-level disinfectants. They are inactivated by soap and by hard water and are not tuberculocidal, so they do not meet the requirement for surfaces contaminated with blood or saliva.
- C. Sodium hypochlorite IS an effective and inexpensive surface disinfectant, but it is used DILUTED — commonly 1:10 to 1:100 for blood spills. At full strength it corrodes metal, damages surfaces and is a significant respiratory irritant.
- D. CORRECT. PHENOLICS act as gross protoplasmic poisons — they precipitate the cell proteins of bacteria and disrupt the cell wall. Among the commonly available agents they offer the broadest combination of bactericidal, fungicidal, TUBERCULOCIDAL and virucidal activity, and they retain activity in the presence of residual organic matter, which is why they are the standard EPA-registered intermediate-level disinfectant for hard smooth surfaces. Note that they are not sporicidal — no surface disinfectant is.
Note: ⚠️ Conflicting sources in the recall itself: the author preferred ‘Lysol’ on a mentor's advice, while the screenshot reproduced in the same file keys PHENOL. The EPA-registered phenolic is the defensible answer; ‘Lysol’ is a brand name spanning several different active chemistries, which makes it a poor exam option. Remember the SPAULDING classification: CRITICAL items (penetrate soft tissue or bone) must be STERILISED; SEMI-CRITICAL (contact mucosa but do not penetrate) sterilised or high-level disinfected; NON-CRITICAL (contact intact skin, plus environmental surfaces) intermediate- or low-level disinfected.
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