Final answer:
The number and rate of new infections depend on factors like pathogen multiplication and immune response. Initially, there may be a period of rapid increase in infections, followed by a decline as the immune system responds. Over time, untreated infections, such as HIV, can lead to a continuous increase in pathogen numbers and decrease in immune cells, represented by a J-shaped growth curve.
Step-by-step explanation:
When tracking the progression of an infectious disease, two key measures are particularly important: the number of new infections, known as incidence, and the rate of new infections over time.
During the initial phase after exposure to a pathogen, such as a virus or bacteria, there's typically an incubation period in which the pathogen begins to multiply, but symptoms have yet to manifest. This can take several days, depending on the disease.
The number of infections and the rate of new infections often escalate swiftly if the pathogen multiplies faster than the body's immune response can manage. This leads to a period of illness where symptoms become pronounced. The immune response then starts to counteract pathogen multiplication, leading to a period of decline where the number of pathogens lowers and symptoms ease.
Overall, the number and rate of new infections are dynamic variables that can change based on factors including the pathogen's characteristics, the host's immune response, and external interventions like vaccinations or antiviral treatments. A J-shaped growth curve often represents the exponential growth of a pathogen in the absence of treatment.