The contamination process of infection follows a specific sequence based on the causative agent. Thus, every infection starts from the locus point of entry. The sequence of contamination includes a causative agent or pathogen, transmission channel, entry portal, and a susceptible host. The diagram below summarizes the sequence of infections. A pathogen or a causative agent must be available for an infection to occur. By implication, organisms that cause or transmit contaminants are called pathogens. Pathogens could be bacterium, viruses, and fungus to mention a few. Specific terminologies describe the pathogen and its mode of transmission. An individual is considered “exposed” if he or she touches the causative agent. However, the individual is infected when the causative agent or pathogen completes the transmission cycle.
Thus, the components of the transmission cycle must be in place to cause infection. However, if one or more variables were absent, the infection would not occur. Consequently, the transmission of the contaminant of the causative agent depends on the dose, virulence, and host resistance. The causative agent must have a mode of transmission, which could be direct or indirect contact. The routes of transmission determine the last stage of infection. By implication, the causative agent could be inhaled, injected, transferred by a vector agent, or blood transmission. If the causative agent locates the portal of entry, it means that the susceptible host is available. Thus, the sequence of transmission is complete when the causative agent or pathogen finds a susceptible host. However, not all infections cause diseases in the susceptible host.