Relationship of Oropharyngeal Colonization Microorganisms to Clinical Outcomes within 100 Days after Allogeneic Hematopoietic Stem Cell Transplantation

•Oropharyngeal colonization microorganisms delay the engraftment of neutrophils and platelets.•Oropharyngeal colonization microorganisms are related to nonrelapse mortality and survival within 100 days in allogeneic hematopoietic stem cell transplantation (allo-HSCT) recipients.•Monitoring of oropharyngeal microorganisms may be useful during the course of allo-HSCT. Little is known about oropharyngeal colonization microorganisms in patients during allogeneic hematopoietic stem cell transplantation (allo-HSCT), and updated epidemiologic investigations are advisable. This study aimed to characterize oropharyngeal colonization microorganisms in patients during allo-HSCT and confirm whether they were related to clinical outcomes. This retrospective, matched case-control study included 1267 consecutive patients undergoing allo-HSCT between January 2018 and December 2020 at our institution. Patients with oropharyngeal colonization microorganisms were those with a positive throat swab before or on the day of transplantation without the occurrence of any symptoms of infection. Propensity score matching was used. Characteristics of oropharyngeal colonization microorganisms were evaluated among patients in the transplant medicine wards and compared with clinical outcomes within 100 days in positive and negative colonization groups. A total of 127 patients had oropharyngeal colonization microorganisms before or on the day of transplantation. Using propensity score matching, we matched the 127 patients in the positive colonization group with 508 patients in the negative colonization group at a 1:4 ratio (total of 635 cases). None of the differences in clinical traits between the 2 groups remained significant. Among the 127 patients with oropharyngeal colonization microorganisms, 90 patients suffered from the documented infection subsequently, and the others were asymptomatic. A total of 82 single gram-negative bacteria were identified in 127 isolates. There were no differences between the positive and negative colonization groups in the occurrence of oral mucositis, Epstein-Barr virus, or acute graft-versus-host disease and relapse within 100 days. However, the rate of neutrophil or platelet recovery was significantly lower in the positive colonization group compared with the negative colonization group (hazard ratio [HR], .71; 95% confidence interval [CI], .59 to .84; P < .001; HR .69; 95% CI, .58 to .83; P = .003; separately). The risk of bloodstream infection was h