To investigate the prevalence of pathogenic bacteria in patients with granulomatous lobular mastitis (GLM) and explore the relationship between Corynebacterium kroppenstedtii (CK) infection and peripheral hematological parameters.

The clinical data and pathogenic bacteria identification by nanopore sequencing of 81 patients with GLM in the Renmin Hospital of Wuhan University from October 2017 to June 2021 were reviewed retrospectively. The enrolled patients were divided into 3 groups according to the pathogenic results: CK-positive group (n=50), CK-negative group (n=19) and non-pathogenic group (n=12). The CK-positive group was further divided into the early-stage subgroup (n=21) and the advanced-stage subgroup (n=29). Counting data is expressed in absolute numbers. The Kruskal-Wallis H test or Mann-Whitney U test was used to compare peripheral white blood cell (WBC) count and neutrophil-to-lymphocyte ratio (NLR) among three groups. The receiver operating characteristic (ROC) curve were plotted to analyze the value of WBC count and NLR in detecting CK infection, and the Kappa test was used to analyze the consistency of WBC count and NLR with nanopore sequencing.

Approximately 85.2% (69/81) of the patients were tested positive by nanopore sequencing, of which 61.7% (50/81) were CK-positive. The proportion of patients with abnormal WBC count in CK-positive group, CK-negative group and non-pathogenic group was 48.0% (24/50), 3/19 and 4/12, respectively, indicating a significant difference (χ²=6.192, P=0.045). The proportion of patients with abnormal WBC count in CK-positive group was significantly higher than that in CK-negative group (χ²=5.997, P=0.043 after Bonferroni correction). The peripheral WBC count in CK-positive group, CK-negative group and non-pathogenic group was 9.09 (7.50, 12.02)×10⁹ cells/L, 7.58 (6.47, 8.20)×10⁹ cells/L, and 7.62 (6.99, 9.84)×10⁹ cells/L, respectively, indicating a significant difference (H=8.748, P=0.013). The peripheral WBC count in CK-positive group was significantly higher than that in CK-negative group (Z=-2.861, P=0.012 after Bonferroni correction). The proportion of patients with WBC abnormality and WBC count in early-stage subgroup were significantly lower than those in advanced-stage subgroup [28.6% (6/21) vs 62.1% (18/29), χ²=5.476, P=0.019; 7.50 (6.74, 10.65)× 10⁹/L vs 9.69 (8.76, 13.67)×10⁹/L, Z=3.155, P=0.002]. (3) The NLR in CK-positive group, CK-negative group and non-pathogenic group was 3.47 (2.67, 5.73), 2.95 (2.04, 3.35) and 3.06 (1.87, 3.37), respectively, suggesting a significant difference (H=9.417, P=0.009). The NLR in CK-positive group was significantly higher than that in CK-negative group (Z=-2.556, P=0.039 after Bonferroni correction). The NLR in early-stage subgroup were significantly lower than that in advanced-stage subgroup [3.27 (1.89, 3.89) vs 4.45 (3.13, 6.86), Z=2.251, P=0.024]. (4) The area under the ROC curve of WBC count was 0.724 (95%CI: 0.599-0.849, P=0.004), and the Kappa coefficient was 0.359. If WBC count > 8.33×10⁹ cells/L, its sensitivity, specificity, accuracy, positive predictive value, negative predictive value, positive likelihood ratio, negative likelihood ratio, Youden index and false negative rate in diagnosing CK-infection were 54.0% (27/54), 94.7% (18/54), 55.6% (45/81), 96.4% (27/28), 43.9% (18/41), 10.260, 0.507, 0.487 and 46.0% (23/50), respectively. The area under the ROC curve of NLR was 0.701 (95%CI: 0.577-0.826, P=0.010), and the Kappa coefficient was 0.313. If NLR>3.13, the sensitivity, specificity, accuracy, positive predictive value, negative predictive value, positive likelihood ratio, negative likelihood ratio, Youden index and false negative rate in diagnosing CK-infection were 68.0% (34/50), 68.4% (13/19), 58.0% (47/81), 85.0% ( 34/40), 44.8% (13/29), 2.153, 0.467, 0.364 and 32.0% (16/50), respectively.

CK is closely related to GLM, and GLM patients with CK infection show high level in hematological inflammation parameters. Clinicians should pay attention to pathogen detection in the diagnosis and treatment of GLM and provide individualized precise regimens.