Using the IRAOS interview, the ABC Schizophrenia Study examined a population-based sample of 232 first illness episodes, representing 84% of 276 first treatment episodes, and a representative subsample of 130 subjects, who were compared with two age- and gender-matched control samples -one from the ''healthy'' population (n = 130), the other first hospitalized with a diagnosis of depressive episode (n = 130).
Survival analysis of the duration of early illness course from onset to first admission as target event revealed a distribution of durations of the early illness course that was markedly skewed to the left. One third (33%) of the broadly defined cases of schizophrenia took less than one year from prodromal onset to develop psychotic symptoms. Only 18% had an acute type of onset of four weeks or less, 15% a subacute type of 4 weeks to one year and 68% a chronic type of onset of one year or more. Only 6.5% started with positive symptoms; 20% presented both positive and negative symptoms within the same month. A prepsychotic prodromal stage with negative or nonspecific symptoms prior to the emergence of the first positive symptom was experienced by 73%.
Nonspecific and negative symptoms started to increase early, positive symptoms quite late, the first of them appearing one year and one month before the climax of the first episode and one year and three months before first admission. In the psychotic episode all three symptom categories accumulated rapidly and reached a maximum followed by almost parallel decreases.
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