Objective: Our objective was to perform a full cohort study of hospital acquired Staphylococcus aureus bacteraemia with extended follow up of hospital survivors after discharge.
Methods: The study population was adults resident in Tayside, Scotland who had a new admission to Ninewells Hospital between 1st July 2005 and 30th June 2006. The cohort enrolled all patients from this population who were admitted to wards where at least one case of S aureus bacteraemia was admitted in the study period. The outcome was mortality up to 30th September 2006 (i.e. at least 90 days after admission), ascertained from the national registry of deaths. Multistate and Cox models were applied to gain insights into ha-S aureus bacteraemia as a time-dependent risk factor.
Results: The cohort included 4,397 patients of whom 34 had ha-MRSA and 27 had ha-MSSA bacteraemia. In total, 230 patients died in hospital and 1044 died by the end of the study period. After adjustment for age, sex and co-morbidity the hazard ratio for death was 3.49 (95% CI: 2.19-5.57) with ha-MRSA and 2.71 (1.53-4.79) with ha-MSSA. In comparison with ha-MSSA, ha-MRSA increased the hazard of death by a factor of 1.29 (0.62-2.68). Cumulative plots showed that S aureus bacteraemia increased the hazard of death for at least 80 days after onset.
Conclusions: Our cohort study has demonstrated that hospital acquired S aureus bacteraemia significantly increases mortality and that the hazard persists beyond the period of hospital stay. The results show the importance of preventing ha-MRSA and ha-MSSA bacteraemias.