What must be present in the chain of infection for an infection to occur?

For an infection to occur, it is essential for each link in the chain of infection to be present in sequential order. The chain of infection consists of several critical components: the infectious agent (pathogen), reservoir (where the pathogen lives), portal of exit (how the pathogen leaves the reservoir), mode of transmission (how the pathogen spreads), portal of entry (how the pathogen enters a new host), and the susceptible host (an individual who can become infected).

If any one of these links is broken, the transmission of infection can be halted. Therefore, all the links must be present and connected in the specific sequence for an infection to take place effectively. Understanding this sequence helps in implementing infection control measures, such as hand hygiene and proper use of personal protective equipment, to prevent the spread of infections.