Mortality after Staphylococcus aureus bacteraemia in two hospitals in Oxfordshire, 1997-2003: cohort study

Abstract

Objective: To determine the incidence of methicillin resistant and methicillin sensitive Staphylococcus aureus (MRSA and MSSA) bacteraemia in inpatients and associated mortality within 30 days after diagnosis.

Design: Anonymised record linkage study of data from hospital information systems and microbiology databases.

Setting: Teaching hospital and district general hospital in Oxfordshire.

Participants: Inpatients aged 18 or over admitted to a teaching hospital between 1 April 1997 and 31 March 2004 and to a district general hospital between 1 April 1999 and 31 March 2004. The main part of the study comprised 216 644 inpatients; patients admitted to haematology, nephrology, or oncology services were not included because most were managed as outpatients.

Outcome measures: Nosocomial MSSA and MRSA bacteraemia; death in hospital within 30 days after bacteraemia.

Results: Rates of S aureus bacteraemia rose between 1997 and 2003, and MRSA was responsible for this increase. Overall mortality 30 days after bacteraemia was 29%. The crude odds ratio for death after MRSA bacteraemia compared with MSSA bacteraemia was 1.49 (95% confidence interval 0.99 to 2.26).

Conclusion: The spread of MRSA has greatly increased the overall number of cases of S aureus bacteraemia and has contributed to short term mortality after S aureus bacteraemia.

Fig 1

Admissions and cases of bacteraemia in two Oxfordshire hospitals, 1997-2003

Fig 2

Changes in rates of nosocomial bacteraemia over time in two Oxfordshire hospitals (n=144 134). Regression lines indicate change over time. Asterisks indicate that the slope of the line is significant (P<0.01; P>0.20 for the others)

Fig 3

Changes in previous isolation of methicillin resistant Staphyloccocus aureus (MRSA), age, and duration of stay over time in two Oxfordshire hospitals (n=144 134). Regression lines indicate change over time. Asterisks indicate that the slope of the line is significant (P<0.01; P>0.20 for the others)

Fig 4

Rates of nosocomial bacteraemia according to previous isolation of methicillin resistant Staphyloccocus aureus (MRSA) in two Oxfordshire hospitals (n=144 134). P<0.01

Fig 5

Rates of nosocomial bacteraemia according to duration of stay (top) and age (bottom) in two Oxfordshire hospitals (n=144 134), log scale. Asterisks indicate that the slope of the regression line is significant (P<0.01; P>0.20 for the others)

Fig 6

Risk of death for inpatients in two Oxfordshire hospitals (n=144 134) according to age and year

Fig 7

Risk of death 30 days after diagnosis of Staphylococcus aureus bacteraemia in two Oxfordshire hospitals (n=144 134)