Clinical performance
Of the 170 patients with suspected BSIs tested by ddPCR, 53 showed positive results, including 23 (13.5%, 23/170) A. baumanniicases, 26 (15.3%, 26/170) K. pneumonia cases, and 4 (2.4%, 4/170) dual infection cases. On the other hand, blood culture detected 4 (2.4%) A. baumannii cases, 7 (4.1%) K. pneumoniacases, and 22 (12.9%) cases with other bacterial infections, with an overall positivity rate of 19.4% (33/170). Of note, all the 11 cases (100%, 11/11) with A. baumannii or K. pneumoniainfections reported by blood culture showed positive results in ddPCR assay. The positivity rate of A. baumannii and K. pneumonia in the ddPCR assay was much higher than that in the blood culture (31.2%, 53/170 vs. 6.5%, 11/170) (Table 7 ).
The clinical characteristics of the 53 ddPCR-positive patients were summarized in Table 3 . No significant differences were observed in age, systolic and diastolic blood pressure, the plasma level of CRP, white blood cell counts, serum creatinine, and use of vasoactive drugs (all P ≥ 0.05) between the patients reported by ddPCR alone (n = 42) and the patients reported by both ddPCR and blood culture (n = 11). Importantly, compared with the 11 positive patients reported by both ddPCR and blood culture, the 42 positive patients reported by ddPCR alone had significantly decreased serum concentrations of procalcitonin (3.70 vs. 12.9 pg/L, P = 0.03) and lactate (2.76vs. 4.26 mmol/L, P = 0.04), APACHE II scores (21.9vs. 27.9, P = 0.02), SOFA scores (10.5 vs. 13.8,P = 0.03), and 28-day mortality rates (70.6% vs. 90.1%,P = 0.04) (Table 3 ). These data suggest that the less severe BSI patients who have been missed by blood culture may benefit from ddPCR test and have better clinical outcomes.