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Unnecessary Antibiotic Usage Linked to Blood Culture Contamination: An Observational Study Across Dutch and US Hospitals

A recent study published in Open Forum Infectious Diseases draws a connection between blood culture contamination in inpatients and elevated incidence of needless antibiotic use. The research, which was retrospective and observational in nature, concerned adult inpatient populations in two Dutch hospitals and five hospitals in the United States. The study aimed to discern the impact of blood culture contamination on antibiotic usage and the utilization of other healthcare resources.

For this analysis, data was obtained from inpatients at these hospitals between January 2016 and December 2019. The only patients included in the study were those who had a minimum of two blood cultures taken during their hospital stay. The researchers then compared clinical outcomes for patients who had positive culture results against those who had negative results. It is worth noting that all hospitals involved in the study had antibiotic stewardship programs in place.

The primary outcome indicated for the research was the total number of in-patient antibiotic therapy days. The researchers employed multivariable logistic regression to assess the influence of blood culture contamination on antibiotic usage. The final pool for analysis comprised of 22,929 patient-admissions, split between 7007 at US hospitals and 15,920 at Dutch medical facilities.

The patients in the study had a mean age of 60.2 years in the US (n=4987) and 58.5 years in the Netherlands(n=12,087). Respective feminine representations stood at 47.0% and 43.2%. When scored using the Charlson comorbidity index (CCI), both cohorts had a median of scores of 7 (IQR, 4-9). US inpatients showed a higher prevalence of a malignancy history (45.5% vs 10.3%) and diabetes (34.6% vs 10.3%).

In terms of blood culture contamination, 4.8% of US patients and 4.1% of Dutch patients had findings indicating contamination. The majority had negative blood cultures standing at 66.3% and 71.8% respectively. The most frequent positive indication was for pneumonia, present in 9.4% of US patients, and 6.9% of Dutch patients.

The analysis found that the mean of additional antibiotic therapy days was higher for patients with positive blood culture contamination results compared to those with negative results in both the Dutch and the US cohorts; 1.58 and 1.74 days respectively and was statistically significant (P <.001). In the US cohort, it was also observed that patients with contaminated blood cultures used intravenous vancomycin significantly more when compared to those with negative cultures (P <.001). The mortality rates during hospital stays and 30-day periods were found not to significantly differ between patients with blood culture contaminations and those without on both patient cohorts.

The researchers acknowledged some limitations in the study, including a lack of data on outpatient antibiotic use, as well as variations in comorbidities and diagnoses for admission between the cohorts. Furthermore, the impact of blood culture contamination on antibiotic usage may have been underestimated. In conclusion, the researchers asserted that despite declines in blood culture contamination (BCC) impacts on patients in recent years, it remains a significant contributor to needless antibiotic usage and healthcare resource utilization. The research was authored by Schinkel M, Boerman A, Carroll K, et al. in the paper titled ‘Impact of blood culture contamination on antibiotic use, resource utilization and clinical outcomes: a retrospective cohort study in Dutch and US hospitals’.


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