Pathogen
A microorganism — bacterium, virus, fungus, or parasite — capable of causing disease in a susceptible host.
The exam rarely asks “what is a pathogen” outright; instead it hands you a scenario and makes you classify the organism’s transmission route to pick the correct PPE. The high-yield tell is the diagnosis: TB, measles (rubeola), and varicella demand airborne precautions (N95 + negative-pressure AIIR), while influenza, pertussis, meningococcus, and mumps need only droplet precautions (surgical mask, private room preferred, spatial separation of at least 3 ft). When a question lists several patients, the airborne pathogen is almost always the priority to isolate first, because the negative-pressure room is the scarcest resource.
The classic trap is confusing the pathogen with its transmission route: a spore-former like C. difficile spreads by contact and resists alcohol gel, so soap-and-water handwashing plus contact precautions is the answer, not hand sanitizer. Another trap is forgetting that one pathogen can need two categories — varicella is airborne and contact. Memory hook: “My Chicken Hez TB” flags Measles, Chickenpox (varicella), Herpes zoster (disseminated), and TB as the core airborne four.
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