Infection is defined as the phenomenon wherein an organism's (host's) body/tissues are invaded by a pathogen. Pathogens are disease-causing agents including, but not limited to, bacteria and viruses.
There are four stages of infection:
- Incubation Period- once the pathogen enters the body, this stage starts already. As the pathogen is inside the host's body, it starts to multiply, and starts growing in numbers. It is also during this period when symptoms of a disease start to manifest. In short, incubation period is the period between the entry of the pathogen to manifestation of non-specific symptoms.
- Prodormal Stage- after the first non-specific symptoms such as colds, or itchyness, among others, the pathogen continues to grow in number. As this happens, the infection progresses. This stage is associated with the period between the manifestation of the first non-specific symptoms to the more sever, and usually more specific symptoms of infection such as rhinitis, or sinus infection, among others. At this point, the host starts to become infectious.
- Illness Stage- this is the highest point or the peak of the infection. Severity of the symptoms increases, particularly the specific symptoms of the particular infection.
- Convalescence or Recovery Stage- acute symptoms will eventually start to disappear for certain diseases. Eventually, the body is cleared of the infection. The recovery stage then starts when symptoms start to disappear, until the host completely recovers to its healthy state.
In summary, the incubation period starts when the pathogen enters the body, the prodormal stage is the stage when the host is infectious, and manifests specific symptoms, the illness stage is when the symptoms become severe and the infection is at its peak, and recovery stage starts when the symptoms gradually start to disappear.