A modular operation theatre for joint replacement surgery delivers laminar unidirectional airflow through ceiling-mounted HEPA filters. What is the defining performance specification of a HEPA filter?

• A Retains 99.97% of particles measuring 0.3 micrometre or larger ✓
• B Retains 99.9% of particles measuring 5 micrometre or larger
• C Kills all airborne bacteria and viruses by electrostatic precipitation
• D Retains 95% of particles measuring 1 micrometre or larger

Explanation

HEPA stands for High Efficiency Particulate Air filtration, defined as retention of at least 99.97% of particles of 0.3 micrometre diameter, the size at which filter penetration is maximal. Option B describes a coarse prefiler standard, and option C is wrong because HEPA filters trap rather than kill microorganisms. This specification underpins ultra-clean air theatres for implant surgery.

Reference: Ananthanarayan and Paniker's Textbook of Microbiology, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.