title: Seasonal variation in the occurrence of delirium in patients admitted to medical units of a general hospital in Italy.
abstract: OBJECTIVE
  Delirium syndrome is common in the hospitalised population. However, data on its aetiological factors are scarce. Clinical observations suggest a relationship between delirium occurrence and seasons. The aim of study was to determine whether a seasonal variation exists in the occurrence of delirium events in-hospital patients.
  
  
  METHODS
  The study included all admissions to the medical units of the Hospital of Ferrara, Italy, between January 2002 and December 2010. On the basis of date admission, cases have been analysed for seasonal variation (four 3-month intervals by seasons) by means of conventional statistics. Moreover, cases categorised into twelve 1-month intervals were also analysed by means of a validated chronobiologic inferential method (single cosinor) to search for cyclic variability.
  
  
  RESULTS
  During the analysed period, the hospital database contained 74 379 records referring to 42 625 subjects (52.7% females). Delirium diagnoses were 1300 (1.7% of total sample), 668 of whom in females (51.4%) and 632 in males (48.6%). Events of delirium were more frequent in winter and autumn (26.6 and 26.5%, respectively) than in spring (23.5%) and summer (23.4%). Chronobiological analysis yielded a significant peak of delirium events in January, when considering both the total raw number of cases and the percent of admissions.
  
  
  CONCLUSIONS
  The study seems to indicate in patients hospitalised in medical units, a higher rate of occurrence of delirium in autumn-winter, similar to that reported for acute medical diseases. The role of possible underlying favouring or triggering factors deserves further research.
authors.affiliation: 1 Department of Internal Medicine, Hospital of Ferrara, Ferrara, Italy.
authors.forename: Massimo
authors.initials: M
authors.lastname: Gallerani
authors.affiliation: 2 Clinica Medica, Department of Medical Sciences and Vascular Diseases Centre, University of Ferrara, Ferrara, Italy.
authors.forename: Roberto
authors.initials: R
authors.lastname: Manfredini