Epidemiologic Triad and Web of Causation

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?

A 35-year-old farmer from rural Odisha presents with fever, chills, and headache for 3 days. Thick and thin blood smears confirm Plasmodium falciparum malaria. The epidemiologic triad for this case includes the parasite (Agent), the patient's immune status (Host), and the structure marked **D** in the diagram. Which of the following best describes the role of the structure marked **D** in malaria transmission in India?

During a foodborne outbreak investigation in Delhi, epidemiologists identify a cluster of cases with acute gastroenteritis linked to consumption of contaminated chicken biryani from a single restaurant. To establish the causative agent and trace the source within the epidemiologic triad (agent → environment → host), which investigation should be prioritized?

In the epidemiologic triad framework, which of the following is the most common environmental factor contributing to the transmission of dengue fever in urban India?