The phrase "a first onset" is correct and usable in written English.
It can be used to refer to the initial occurrence or beginning of something, often in medical or psychological contexts.
Example: "The study focused on the factors that contribute to a first onset of anxiety disorders in adolescents."
Alternatives: "an initial occurrence" or "the first occurrence".
The first group included 71 (45.5%) patients with a first onset of rheumatic fever (ARF), the second group 86 (54.5%) patients with a recurrent rheumatic fever (RHD).
The key difference between a 'prodrome' and 'risk syndrome' is that the former is primarily a predictor of the onset of an episode of the mental disorder under examination, whilst the latter is primarily a predictor of the overall likelihood that someone will experience a first onset of a disorder (compared to no disorder or another disorder).
The pathways to care in a first onset psychosis are diverse and may influence the chances of early treatment and therefore the duration of untreated psychosis.
An early detection programme aimed at staff in non-health service community organisations was well-implemented but ineffective in reducing duration of untreated psychosis or improving pathways to care for people experiencing a first onset of psychosis.
In combination with the rarity of the syndrome and thus the likeliness to become confronted with a first onset of the syndrome unprepared clearly makes it a challenge even for experienced anaesthesiologists [ 12].
In general, the probability of a first onset of depressive disorder after childhood adversities tended to decrease over time (mean reduction in effect 56%%), while no such time-dependent decrease was found for anxiety disorders.
Mishin et al. (2001) found for several substorms that a pattern in which an "initial onset" (which they identified with pseudobreakups or trigger bays) took place at low latitude, followed by a "second onset" at higher latitude.
For higher intensities (Fig. 2C), a second onset spike, or chop, emerges, followed by some sustained activity.
59 Disability resulting from medical or neurological illnesses is associated with increased risk for a first-onset depressive disorder.
For example, we recently saw a case of 'spice encephalopathy' that presented as a first-onset seizure but had features of serotonin syndrome (myoclonus, dilated pupils).
In example (a), the first onset of the rupture of the small patches is delayed, but it propagates very rapidly once it has started.
