Standard vs transmission-based precautions: which pathogen needs which

Standard precautions are the floor for every patient. Transmission-based precautions are added on top, and the CCMA asks you to pick the right category from a clinical picture before any laboratory result exists. Almost every miss on this material comes from one of three things: treating standard precautions as something you apply only to patients already known to be positive, offering a surgical facemask where a fit-tested N95 is required, or forgetting the organisms that need two categories at the same time.

Standard precautions	Every patient, every setting, every time — no known or suspected infection is required (CDC 2007 Guideline for Isolation Precautions)
What standard precautions include	Hand hygiene, PPE chosen by anticipated exposure, respiratory hygiene and cough etiquette, safe injection practices, and safe handling of contaminated equipment and surfaces
Contact	Gown and gloves before entering the room: C. difficile, MRSA, VRE, scabies, lice, RSV, norovirus, uncontained draining wounds
Droplet	Surgical facemask on room entry, single room, NO special ventilation: influenza, pertussis, mumps, rubella, Neisseria meningitidis, group A strep
Airborne	Airborne infection isolation room plus a fit-tested N95 or higher: tuberculosis, measles (rubeola), varicella, disseminated zoster
Two categories at once	Varicella and disseminated herpes zoster require airborne AND contact — the vesicle fluid is infectious too, so a respirator alone covers only half the risk
AIIR specifications	Negative pressure, at least 12 air changes per hour (at least 6 in construction predating 2001), air exhausted outdoors or HEPA-filtered (CDC Guideline for Environmental Infection Control)
N95 requirements	Fit-tested for that exact make, model and size before first use and at least annually (OSHA 29 CFR 1910.134(f)(2)), plus a user seal check every single time it is put on
C. difficile	Contact precautions, handwashing with soap and water, and an EPA List K sporicidal disinfectant — alcohol rub and quaternary ammonium products do not kill spores
Measles in the room	Room air stays infectious for up to 2 hours after the patient leaves, which is why the room is not turned over immediately

Where the point is lost: The word "mask" is the trap. Droplet precautions call for a surgical facemask that anyone can put on and take off; airborne precautions call for a fit-tested, NIOSH-approved N95 or higher plus a negative-pressure room, because a surgical mask does nothing against droplet nuclei suspended in air. If the stem names tuberculosis, measles, varicella or disseminated zoster and an answer choice says "surgical mask," that choice is wrong no matter how sensible the rest of it reads. The second trap is timing: precautions are started empirically on clinical suspicion, never held until the laboratory confirms.