A Retrospective Evaluation of Critical Care Blood Culture Yield - Do Support Services Contribute to the "Weekend Effect"?
BACKGROUND
The "weekend effect" describes an increase in adverse outcomes for patients admitted at the weekend. Critical care units have moved to higher intensity working patterns to address this with some improved outcomes. However, support services have persisted with traditional working patterns. Blood cultures are an essential diagnostic tool for patients with sepsis but yield is dependent on sampling technique and processing. We therefore used blood culture yield as a surrogate for the quality of support service provision. We hypothesized that blood culture yields would be lower over the weekend as a consequence of reduced support services.


METHODS
We performed a retrospective observational study examining 1575 blood culture samples in a university hospital critical care unit over a one-year period.


RESULTS
Patients with positive cultures had, on average, higher APACHE II scores (p = 0.015), longer durations of stay (p = 0.03), required more renal replacement therapy (p<0.001) and had higher mortality (p = 0.024). Blood culture yield decreased with repeated sampling with an increased proportion of contaminants. Blood cultures were 26.7% less likely to be positive if taken at the weekend (p = 0.0402). This effect size is the equivalent to the impact of sampling before and after antibiotic administration.


CONCLUSIONS
Our study demonstrates that blood culture yield is lower at the weekend. This is likely caused by delays or errors in incubation and processing, reflecting the reduced provision of support services at the weekend. Reorganization of services to address the "weekend effect" should acknowledge the interdependent nature of healthcare service delivery.
Department of Clinical Sciences, Respiratory Infection Group, Liverpool School of Tropical Medicine, Liverpoool, United Kingdom; Aintree University Hospitals NHS Foundation Trust, Liverpool, United Kingdom.
Ben
B
Morton
Aintree University Hospitals NHS Foundation Trust, Liverpool, United Kingdom.
Shankara
S
Nagaraja
Department of Clinical Sciences, Respiratory Infection Group, Liverpool School of Tropical Medicine, Liverpoool, United Kingdom; Royal Liverpool University Hospital, Liverpool, United Kingdom.
Andrea
A
Collins
Department of Clinical Sciences, Respiratory Infection Group, Liverpool School of Tropical Medicine, Liverpoool, United Kingdom.
Shaun H
SH
Pennington
Department of Clinical Sciences, Respiratory Infection Group, Liverpool School of Tropical Medicine, Liverpoool, United Kingdom; Aintree University Hospitals NHS Foundation Trust, Liverpool, United Kingdom.
John D
JD
Blakey
D039602:After-Hours Care; D000368:Aged; D001424:Bacterial Infections / Q000097:blood / Q000175:diagnosis* / Q000382:microbiology; D001769:Blood / Q000382:microbiology*; D003422:Critical Care; D000066891:Critical Care Outcomes; D003951:Diagnostic Errors / Q000517:prevention & control*; D004636:Emergency Service, Hospital / Q000706:statistics & numerical data*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D013048:Specimen Handling