松下 一之

症例は70歳代女性。悪寒、嘔吐、食思不振、発熱から急性胆嚢炎が疑われ、当院消化器内科に緊急入院した。入院時血液培養のうち、嫌気ボトルが培養44時間で陽転し、アネロコロンビアウサギ血液培地(日本BD)での培養で、極微小の透明なコロニーが観察され、質量分析と16S rRNA遺伝子解析によってDialister pneumosintesと同定された。本菌はVeillonella科に属し、腸管、口腔内、腟などに常在する偏性嫌気性グラム陰性桿菌である。Dialister属はヒトに対する病原性については不明な点が多い。本菌の症例報告は2002年から2023年の間で、国内外から12報14症例とまれである。本菌は発育が遅く、全自動同定感受性装置の同定可能菌種に含まれておらず、現状は質量分析や16S rRNA遺伝子解析による同定のみのために症例報告数が少ないことが予想される。今後はより多くの症例情報を蓄積し、ヒトへの病原性の有無や薬剤感受性検査法の確立を行うことが必要である。(著者抄録)

The effect of antibodies elicited by bivalent mRNA vaccines (original and omicron BA.1) on preventing coronavirus disease 2019 (COVID-19) onset in the presence of the XBB variant remains unknown. A prospective cohort study conducted at Chiba University Hospital examined healthcare workers who received their sixth vaccination with the Pfizer-BioNTech COVID-19 bivalent mRNA vaccine (original and omicron BA.1). Researchers quantitatively measured serum anti-spike (S) antibody levels. Participants not infected during the 60-day observation period after vaccination had significantly higher S antibody titers than those who were newly infected (27756 U/mL, 95% CI [24988-30831 U/mL] vs. 15321 U/mL, 95% CI [10824-21688 U/mL], p<0.05). The risk of infection decreased by 84% when the S antibody titer exceeded 15500 U/ml. Neutralizing antibody titers against the XBB.1.16 and XBB.1.42 variants were higher in age- and sex-matched noninfected individuals than in newly infected individuals during the post-vaccination observation period. S antibody titers were highly correlated with neutralizing antibody titers. In conclusion, after the sixth COVID-19 vaccination with the bivalent mRNA vaccine (original and omicron BA.1), high S antibody titers correlated with disease prevention, even in the presence of XBB variants.