Prevalence of shift work disorder among hospital personnel: A cross-sectional study using objective working hour data

The prevalence of shift work disorder (SWD) has been studied using self-reported data and the International Classification of Sleep Disorders, Second Edition (ICSD-2) criteria. We examined the prevalence in relation to ICSD-2 and ICSD-3 criteria, work schedules and the number of non-day shifts (work outside 06:00–18:00 hours) using objective working-hours data. Secondly, we explored a minimum cut-off for the occurrence of SWD symptoms. Hospital shift workers without (n = 1,813) and with night shifts (n = 2,917) and permanent night workers (n = 84) answered a survey (response rate 69%) on SWD and fatigue on days off. The prevalence of SWD was calculated for groups with ≥1, ≥3, ≥5 and ≥7 monthly non-day shifts utilizing the working hours registry. ICSD-3-based SWD prevalence was 2.5%–3.7% (shift workers without nights), 2.6%–9.5% (shift workers with nights) and 6.0% (permanent night workers), depending on the cut-off of non-day shifts (≥7–1/month, respectively). The ICSD-2-based prevalence was higher: 7.1%–9.2%, 5.6%–33.5% and 16.7%, respectively. The prevalence was significantly higher among shift workers with than those without nights (p-values <.001) when using the cut-offs of ≥1–3 non-day shifts. Shift workers with nights who had ≥3 days with ICSD-3-based SWD symptoms/month more commonly had fatigue on days off (49.3%) than those below the cut-off (35.8%, p <.05). The ICSD-3 criteria provided lower estimates for SWD prevalence than ISCD-2 criteria, similarly to exclusion of employees with the fewest non-day shifts. The results suggest that a plausible cut-off for days with ICSD-3-based SWD symptoms is ≥3/month, resulting in 3%–6% prevalence of SWD.