December 29, 2021
By Zeina A. Kanafani, MD, MS, FIDSA
Patients with SARS-CoV-2 infection who require hospital admission, particularly admission to the intensive care unit (ICU), are at high risk for developing secondary bacterial infections. However, diagnosis of these bacterial coinfections is made challenging by the relatively high blood culture contamination rate.
In this retrospective study conducted in Japan and published in the American Journal of Infection Control, the investigators compared blood culture contamination rates in adult hospitalized patients during the pre-pandemic period (Pre-PP) to the pandemic period (PP). The number of positive blood cultures in ICU and non-ICU patients were counted from April 1, 2019, to Dec. 31, 2019 (Pre-PP), and from April 1, 2020, to Dec. 31, 2020 (PP). The infection control team made the determination of true infection versus contamination. The total number of blood cultures was 1,040 during Pre-PP (0.01 per patient-day) and 918 during PP (0.02 per patient-day). There were 179 positive blood cultures during pre-PP (17.2%; 95% confidence interval [CI], 15.0%-19.6%) and 105 during PP (11.4%; 95% CI, 9.5%-13.7%; P = .0004). However, there was no statistical difference in true bacteremia per patient-day between the two study periods. Regarding contamination rates, there were 3.7% contaminations during Pre-PP and 6.1% during PP (P = .015), translating into 0.00005 per patient-day during Pre-PP and 0.0012 during PP (P < .0001). The same was true in the ICU, where both the percentage of contaminations and the rate of contamination per patient-day were significantly increased during PP compared to Pre-PP (5.0% and 0.002 per patient-day vs. 9.0% and 0.016 per patient-day, respectively).
The authors therefore found an increase in true bacteremias during PP but also an increase in contaminated blood cultures. Possible explanations include increased workload during the pandemic and the inconvenience of caring for patients while wearing personal protective equipment. Given the clinical and financial implications of contaminated blood cultures, strategies should aim at improving the process of obtaining blood cultures and reducing the risk of contamination.