Influence of house-staff experience on teaching-hospital mortality: the "July phenomenon" revisited.

BACKGROUND: The "July phenomenon" refers to a purported worsening of outcomes in teaching-hospital patients with the arrival of new, inexperienced house-staff. Previous quantitative studies of new house-staff and increased mortality have been limited primarily by a focused patient population and the use of limited data to adjust for severity of patient illness.
METHODS: We included all medicine, surgical, and obstetrical patients admitted to a teaching hospital in Ontario, Canada between April 15, 2004 and December 31, 2008. We calculated the ratio of observed to expected weekly number of deaths in hospital. The expected number of deaths was calculated using a validated, discriminative, and well-calibrated multivariate survival model. Collective house-staff experience was modeled from a minimum on July 1st to a maximum on June 30th using five distinct patterns.
RESULTS: We studied 259,748 encounters that included 164,318 people. The mortality rate was 3.0%. The ratio of observed to expected number of weekly deaths was not associated with collective house-staff experience, irrespective of the pattern in which it was modeled. The lack of association between risk of death in hospital and house-staff experience did not vary by admission type (urgent vs elective) or specialty (medicine vs surgery).
CONCLUSION: At our hospital, we found no association between the arrival of new house-staff and the adjusted risk of death in hospital. These data, along with the results of the vast majority of previous studies in this field, make the existence of the "July Phenomenon" for inpatient mortality extremely unlikely.