To evaluate the value on time to positivity (TTP) for blood culture combined with inflammatory parameters including immature granulocytes percentage (IG%), immature granulocyte count (IG#), C-reactive protein (CRP), white blood cells count (WBC) and neutrophil percentage (NE%) to identify bloodstream infection from contamination with coagulase-negative Staphylococci (CoNS) in pediatric patients.

Data of 12 897 inpatients with blood culture from January to December 2019 in Guangzhou Women and Children’s Medical Center, Guangzhou Medical University were collected and analyzed, retrospectively. According to the definition of nosocomial infection surveillance issued by Centers for Disease Control and Prevention of the United States in 2016, they were divided into CoNS infection group (132 cases) and CoNS contamination group (124 cases). Cases with Staphylococcus aureus positive at the same period were collected as positive control (SA group, 27 cases). ROC curve was used to analyze the application value of TTP combined with the above-mentioned inflammatory parameters to distinguish CoNS infection from contamination.

Among the 256 strains of CoNS isolated from bloodstream, the top three common strains were Staphylococcus hominis (76 cases, 55.1%), Staphylococcus epidermidis (38 cases, 32.0%) and Staphylococcus capitis (10 cases, 7.0%). There was no significant difference of CoNS subspecies distribution between CoNS infection group and CoNS contamination group (χ²= 6.0, P = 0.647). The parameters TTP, CRP, WBC, IG%, IG# and NE% of the three groups were significantly different (H = 82.7, 13, 11.3, 25.8, 25.7, 8.5; all P < 0.05). TTP of CoNS infection group was significantly lower than that of contamination group [22.4 (17.6, 31.1) h vs. 31.1 (25.3, 41.3) h; U = 496.0, P < 0.001]. IG% [0.5 (0.3, 0.8) vs. 0.3 (0.2, 0.5); U = 1 603.5, P < 0.001], IG# [0.04 (0.02, 0.09) × 10⁹/L vs. 0.03 (0.02, 0.05) × 10⁹/L; U = 1 767.0, P < 0.001], CRP [9.0 (1.1, 32.1) mg/L vs. 4.2 (0.6, 15.4) mg/L; U = 1 964.0, P = 0.001], NE% [48 (32.8, 65.0) vs. 44 (28.5, 59.5); U = 2 445.0, P = 0.036] were higher than those of contaminattion group, while WBC [10.1 (6.9, 13.3) vs. 9.2 (7.0, 11.6) × 10⁹/L] was not significantly different between the two groups (U = 2 907.5, P = 0.645). There was no statistical difference of those parameters between CoNS infection group and SA control group (all P > 0.05). There was significant difference in those parameters between CoNS contamination group and SA control group (all P < 0.05). ROC analysis showed that the value of TTP in identifying CoNS infection from contamination was the biggest area under the curve (AUC = 0.913) and the sensitivity and specificity were 82.7% and 85.2%, respectively, at the optimal Cut-off value of 23.9 hours. It was followed by IG% (AUC = 0.712), with the optimal critical value of 0.55%, the sensitivity of 51.9% and specificity of 79.7%. All the AUC of IG#, CRP and NE% were less than 0.7. The combination of TTP with IG% and CRP could improve the AUC, sensitivity, specificity, accuracy, PPV and NPV to 0.972, 88.3%, 0.942, 91.4%, 92.2% and 87.0%, respectively.

TTP within 24 hours indicates the possibility of CoNS as the pathogenic agent in blood culture for pediatric patients, and the combination of TTP with IG% and CRP could improve the diagnostic accuracy.