"initial onset" is a correct and usable phrase in written English.
You can use it when referring to the start of something or the beginning of a process. For example, "We have seen an initial onset of more pleasant weather."
Time to initiation of low-dose corticosteroid therapy was defined as the time from the initial onset of septic shock-related hypotension to the initiation of corticosteroid.
Stressful life experiences may trigger the disease's initial onset.
Rett syndrome causes progressive disabilities in intellectual and motor development, with the initial onset of symptoms usually appearing in infancy, between the 6th and 18th months of life.
None of the patients linked dental care to the initial onset of their eating disorders.
Clinical symptoms are broadly characterized by initial onset, and progressive debilitating neurological impairment.
The initial onset temperature of volatilization for JME was around 120°C.
Employing the implicit priming task, we examined whether Chinese words that shared the initial onset consonant could be typed, using the phonetic-based method (called zhuyin), with faster response times than words that did not share the initial onset consonant.
Certain patients, however, experience persistent joint symptoms for weeks or months and, occasionally, years after the initial onset of illness.
Major depression and dysthymia are frequent, debilitating, and chronic disorders, whose highest rate of initial onset is during the late adolescent years.
Denudation rates also display high temporal variability, with much surface evolution having perhaps occurred soon after the initial onset of glaciation or during paraglacial phases.
At the initial onset of the perturbation all field lines oscillate with about the same phase and the wave field is characterized by a predominantly poloidal polarization.
