Cost containment and quality of care considerations have increased research interest in the potential preventability of early re-hospitalisations. Various registry-based retrospective cohort studies on psychiatric re-hospitalisation have focused on the role of early post-discharge service contacts, but either did not consider their time-dependent nature ('immortal time bias') or evaded the issue by analysing late re-hospitalisations. The present study takes care of the immortal time bias in studying early psychiatric re-hospitalisations. In a retrospective cohort study using nationwide electronic claims data in Austria, 10,689 adults discharged from acute psychiatric inpatient wards were followed up for 30days. Cox regression analyses were performed with post-discharge psychiatric and general practitioner contacts as time-dependent covariates and time to first psychiatric re-hospitalisation as outcome. Post-discharge ambulatory physician contacts were significantly associated with a decreased psychiatric re-hospitalisation rate (hazard ratio 0.77 [95% CI 0.69; 0.87], p<0.0001), with similarly strong contributions to this association by general practitioners and psychiatrists. Despite avoiding the immortal time bias and controlling for several confounders, we suggest to be cautious with a causal interpretation of the identified association, since potentially relevant confounders, such as disease severity, were unavailable in our claims data base.
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