Epidemiologic Triad and Web of Causation

A 32-year-old woman from rural Maharashtra presents with fever, joint pain, and rash 5 days after a mosquito bite during monsoon. Suspected dengue fever. Which investigation is the most appropriate to confirm the diagnosis during the acute phase (day 5 of illness)?

During a tuberculosis outbreak investigation in a crowded urban slum, epidemiologists need to identify the source case and trace the chain of transmission. Which investigation is most appropriate to establish the epidemiologic link between suspected cases and confirm recent transmission?

A public health team is investigating a foodborne outbreak of *Salmonella* in an urban slum in Delhi. All of the following represent components of the epidemiologic triad relevant to this outbreak EXCEPT:

A public health officer is comparing the epidemiologic patterns of tuberculosis (TB) and measles in a rural Indian district. Which feature best distinguishes the web of causation of TB from that of measles?

In the epidemiologic triad model, which component represents the physical or biological environment that allows transmission of an infectious agent?