The day to day description of the successive stage of a disease is called its natural history. It begins with the account of susceptibility stage and ends with its final resolution.
The point in time that the said changes are initiated to the time the concerned host [potential patient] comes down with disease is called the “pre-pathogenic phase.’ This is the “susceptibility stage” of the disease.
There may be a sub-clinical phase at the outset. In the case of diseases this is known as the incubation period. It is defined as the interval between the entry of the pathogenic organism and the appearance of the clinical manifestations.
In some cases, they may remains wholly in the subclinical phase, the so-called subclinical infection.
The subclinical stage gives way to the “prodromal stage.” In this the patient has vague signs and symptoms. It is difficult to make a diagnosis, and that why Raila was busy transferencing
After a few days typical features developed a case when Raila said he was fatigued and feverish hence rushed to Nairobi hospital, and the diagnosis was readily made after under going Covid-19 test. This is the stage of overt disease.
After a variable length of time, which for Raila, was three weeks, the signs and symptoms gradually subside after primary or secondary interventions. And the patient enters the stage of defervescence, and then follows the final stage of convalescence.
In some cases however the end-result is not recovery but chronicity, permanent disability or death.