Abstract
Acinetobacter species are not considered skin commensals and under-treatment is an overriding concern when caring for critically-ill patients who are mostly at risk of extensively drug-resistant Acinetobacter baumannii (XDRAB) infections. Hence even a single blood culture yielding XDRAB will tend to prompt intervention. However, field observations suggest that patients with single-positive blood cultures had milder disease and were more likely to be recruited in interventional studies than those with multiple-positive blood cultures, yet no distinction is made in current clinical or trial recruitment practices. To our knowledge, this is the first study to compare the clinical characteristics and outcomes of patients with single-positive versus multiple-positive blood cultures for XDRAB. In this multicenter prospective cohort study of XDRAB bacteremic patients from July 2010 to June 2015, only patients with at least two simultaneously drawn blood cultures were included. The patients were classified as having single-positive or multiple-positive blood cultures according to the number of positive blood cultures yielding XDRAB. The primary end-point was the 28-day mortality. Of a total of 155 patients enrolled, 69 had a single-positive and 86 had multiple-positive blood cultures. Leukopenia (37.2% vs. 16.2%; P = 0.004), thrombocytopenia (56.0% vs. 26.5%; P < 0.001), higher Pitt bacteremia scores (6.6 vs. 5.5, P = 0.03) and higher 28-day mortality rates (70.9% vs. 43.5%; P = 0.001) distinguished patients with multiple-positive from those with single-positive cultures. Multivariate logistic regression showed that multi-positivity independently predicted 28-day mortality (adjusted odds ratio, 2.34; 95% confidence interval (CI), 1.03–5.28; P = 0.04) and the Cox regression confirmed that multi-positivity (adjusted hazard ratio, 1.80; 95% CI, 1.13–2.85; P = 0.01) predicted rapid mortality. Patients with multiple versus single positive blood cultures yielding XDRAB had greater morbidity and mortality. Investigators and clinicians should be aware that the blood culture positivity rate impacts outcomes of XDRAB bacteremia.
Highlights
Drug-resistant Acinetobacter baumannii (XDRAB) bacteremia usually occurs in severely ill patients in the intensive care unit with limited therapeutic options [1, 2]
The multiple-positive blood culture group had a higher frequency of underlying malignancy (36.0% vs. 20.3%; P = 0.030), leukopenia (37.2% vs. 16.2%; P = 0.004), thrombocytopenia (56.0% vs. 26.5%; P < 0.001), and pneumonia (48.8% vs. 30.4%; P = 0.020), higher initial disease severity, and correspondingly higher rates of 14-day (P = 0.006) and 28-day mortality (70.9% vs. 43.5%; P = 0.001)
The differences in mortality between single versus multiple-positive patient groups might be explained by higher bacterial load since semi-quantitative blood cultures have been shown to be a measure of the magnitude of S. aureus bacteremia [18] and Chuang et al have shown that the bacterial burden measured by real-time PCR is associated with the in-hospital mortality of A. baumannii bacteremia [17]
Summary
Drug-resistant Acinetobacter baumannii (XDRAB) bacteremia usually occurs in severely ill patients in the intensive care unit with limited therapeutic options [1, 2]. Few studies have focused on the impact of bacterial factors. Identified factors such as the Acinetobacter genospecies and serum OXA-51 DNA load require molecular tools too sophisticated for daily clinical practice [16, 17]. The blood culture positivity rate is an easy observation that has proven to be a semi-quantitative measure of the magnitude of Staphylococcus aureus bacteremia and to predict mortality in such patients [18]. The prognostic validity of the blood culture positivity rate is not universally applicable, as demonstrated by the similar clinical outcomes of patients with single versus multiple-positive blood cultures of enterococci or coagulase-negative staphylococci (CoNS) [19, 20]
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