インフルエンザワクチンを毎シーズン連続して接種するとワクチン効果が減弱するかもしれないという議論がある．我々は，過去の感染を考慮したうえでこの現象を検討する臨床疫学研究を行った．その結果，9～ 18 歳の若年者において，連続接種者のワクチン効果は当該シーズンのみ接種したものに比べ，優位に低いことが示された．また，ワクチン効果は過去のワクチン接種回数に用量依存的に低下していた．この現象は，ワクチン株間の抗原差が小さく，ワクチン株と流行株の抗原差が大きくなった場合（抗原変異）に若年者におこりやすい可能性があり，更なる検討が必要である.

【背景】日本では新生児侵襲性B 群連鎖球菌（Group B Streptococcus 以下GBS）感染症防止のため，2008 年に予防プログラムが開始され，日本の2011～2015 年調査での罹患率は早発型0.09，遅発型0.12/1000 出生であった．産婦人科診療ガイドライン―産科編2017 改訂版（GL2017）では，妊娠35～37 週に膣と肛門内からの培養検査を行い，GBS 保菌妊婦には分娩時に抗菌薬の静脈投与，培養にはGBS 選択分離培地を推奨している．GL2017 策定後の実態調査はなされていない．
【目的】各産科施設のGBS スクリーニング検査方法の実態を調べるため，アンケート調査を行う．
【方法】米国Vanderbilt 大学開発データ集積管理システムREDCap により情報を集積する．各施設での検体採取時期，部位，培養法，予防的抗菌薬投与法など11 項目について分娩を取り扱う産科施設からの回答をREDCap に入力し，解析した．
【結果】430 施設中237 施設より回答を得た（55.1%）．うち50 施設はGL2017 で推奨されている35 週以降に培養を実施しておらず，141 施設は同推奨の膣と肛門内の2 か所から採取されていなかった．分娩時に予防的抗菌薬を静脈内投与していたのは214 施設（90.3%）であった．培養方法は直接法127 施設，増菌法 64 施設であった．GL2017 推奨の，妊娠35～37 週に膣，肛門内2 か所からの培養検査を行い，保菌妊婦の分娩時に予防的抗菌薬静脈投与していた施設は，77 施設（32.5%）であった．このうち，GBS 検出率が最も高く，米国で推奨されているGBS 選択増菌培地を採用している施設は15 施設（6.3%）であった．
【結論】早発型GBS 感染症の発症を最小限にするため，適切な妊婦GBS 保菌スクリーニング法のガイドライン遵守とGBS 選択増菌培地の採用による検出率向上が望まれる．

A 53-year-old man was admitted with fever and generalized malaise.
Computed tomography (CT) revealed slight swelling of the right pectoralis major muscle. He was diagnosed as having pyomyositis. Blood and abscess fluid cultures were positive for Staphylococcus schleiferi (S. schleiferi). Empiric antibiotic therapy was initiated with intravenous ceftriaxone (CTRX). However, the highgrade fever persisted, and the right chest wall became swollen. On day 4, CT demonstrated abscesses in the right pectoralis major muscle and the front of the right thoracic cavity. The abscesses were drained and intravenous sulbactam/ampicillin (SBT/ABPC) treatment was initiated. With this treatment, although the abscesses became smaller, the high fever persisted. On day 10, CT revealed another abscess in the back of the right thoracic cavity, which was also drained. After the second drainage, the patientʼs condition improved and his serum CRP level decreased. He was discharged on day 24 of hospitalization. Pyomyositis is a bacterial infection of the skeletal muscle, and the quadriceps muscles are the most frequently affected. There have been 5 reports of adult cases of pyomyositis of the pectoralis major muscle in Japan, and the causative organism in all 5 cases was Staphylococcus aureus (S. aureus) . S. schleiferi is a beta-hemolytic, coagulasevariable colonizer of small animals that can cause opportunistic infection in humans. This is the first report of pyomyositis of the pectoralis major muscle caused by S. schleiferi in a Japanese patient.

We successfully treated a patient on maintenance hemodialysis who was diagnosed as having prosthetic valve endocarditis (PVE) caused by Streptococcus salivarius (S. salivarius) with low penicillin susceptibility, using the combination of ceftriaxone with gentamicin at a synergy dose. The patient, a 73-year-old man with end-stage renal disease on maintenance hemodialysis, was referred to our department after 3 days of treatment with oral amoxicillin for fever and chills. Two initial blood cultures were positive for S. salivarius. Transesophageal echocardiography (TEE) performed at admission to our hospital revealed a 0.6-cm vegetation attached to the aortic prosthetic valve. The patient was diagnosed as having PVE caused by S. salivarius, and initiated on treatment with intravenous ampicillin at the dose of 2g every 12 hours with concurrent intravenous gentamycin administration at the dose of 50mg after the commencement of each hemodialysis session. Sensitivity testing revealed intermediate resistance of the causative organism to penicillin and ampicillin. Therefore, the therapy was switched to intravenous ceftriaxone 2g every 24 hours for 6 weeks, with concurrent gentamicin administration at 50mg after the commencement of hemodialysis session. However, gentamicin needed to be discontinued after 18 days because of hearing loss. A repeat TEE at discharge of the patient confirmed disappearance of the vegetation on the prosthetic valve. We conclude that decisions regarding therapeutic and prophylactic interventions for infective endocarditis caused by S. salivarius should be made taking into account the possibility of penicillin resistance of the causative organism.

We report the case of a 78-year-old male patient with decompensated liver cirrhosis who died from exacerbation of the liver cirrhosis after recovery from severe fever with thrombocytopenia syndrome (SFTS). The patient visited our hospital with complaints of fever, appetite loss, diarrhea and lightheadedness. Laboratory examination revealed leukopenia, thrombocytopenia, elevation of the liver enzyme levels, and hyponatremia. The patient was diagnosed as having SFTS by RT-PCR. He gradually recovered with supportive treatment and was discharged on day 68 after admission. However, he was readmitted 30 days later with generalized weakness and behavioral abnormalities. He died on day 135 after readmission due to progression of liver failure. This case suggests the need for further investigation to clarify the long-term course after recovery from SFTS and the influence of SFTS on pre-existing comorbidities.