"initial occurrence" is correct and usable in written English.
You can use it when referring to the first occurrence of something. For example, "The initial occurrence of this illness was noticed months ago."
At the end of September 1998, following the initial occurrence of neurologic cases of unknown origin in horses, we initiated a retrospective study to assess possible common exposures.
This study aimed to explore the genetic aspect of its initial occurrence.
Thus therapeutic interventions designed to prevent the initial occurrence of the arrhythmia are particularly needed.
Each type of lesion, however, disrupted the initial occurrence of neophobia to the taste stimulus.
Furthermore, media coverage was persistent, with references made to the CEO's actions up to an average of 4.9 years after initial occurrence.
And I think that the point Clarke makes is when you have an initial occurrence that has never happened before, some people might see it and try to warn about it, but most people would find it unlikely, impossible.
In the same year, direct radiological examination identified initial occurrences of osteoarthritis in the distal interphalangeal joints of both thumbs; subsequent examinations carried out during 2007 found a worsening of the radiological status with a reduction of joint lines.
From the 100 677 initial occurrences, we compiled a dataset of 38 936 (∼40 %) unique occurrences combining species with accurate geolocation: 11 845 from herbarium, 7420 from plots, 18 390 observations and 1281 photographs, used thereafter to describe the known distribution of tree species in New Caledonia.
It may be that the risk factors for initial SSTI occurrence differ from those that predispose to continued colonization with or re-exposure to pathogenic bacteria.
As discussed previously, the availability of a GABHS vaccine would be the best form of ARF prevention, especially since not all patients report upper respiratory infection symptoms or sore throat before their initial ARF occurrence.
In that study, accounting for follow-up time, chronic skin conditions such as psoriasis and lymphedema, presence of an intravenous catheter, and lack of virologic suppression were most strongly associated with initial SSTI occurrence.
