日本新生児成育医学会雑誌　34(2)：171-175；2022　

日本新生児成育医学会雑誌　第34巻　第2号　50 ～ 54頁（2022年）

受付日：2021．12．16

受理日：2022．03．25

健常乳児のAchromobacter xylosoxidans 菌血症の1 例

Achromobacter Xylosoxidans Bacteremia in a Healthy Infant：A Case Report

日本赤十字社医療センター　小児科

Department of Pediatrics, Japanese Red Cross Medical Center

西澤会美奈・宮奈　香・渡邊康博・大石芳久

Emina NISHIZAWA，Kaori MIYANA，Yasuhiro WATANABE，Yoshihisa OISHI

Key Words：Achromobacter xylosoxidans，bacteremia，healthy infant，multi-drug resistance

Achromobacter xylosoxidansは環境中に遍在する多剤耐性グラム陰性桿菌で，免疫能が低下した患者に医療関連 感染症を引き起こすが，健常乳児の院外感染は極めてまれである。今回我々は基礎疾患のない2 か月男児のA. xylosoxidans 菌血症の1 例を経験した。発熱で来院し全身状態は良好であったが血液検査で白血球数21,810/μL， CRP 3.34mg/dL と炎症反応の上昇を認めた。菌血症を疑いセフトリアキソンの投与を開始したが，血液培養で A.xylosoxidans が検出されピペラシリンに変更し治療を完遂し合併症なく退院した。免疫グロブリン値や補体価は 正常であったが，感染経路は不明であり，今後の経過を慎重に観察する必要がある。A.xylosoxidans は多剤耐性で， 新生児から早期乳児に一般的に使用される抗菌薬に耐性を持つため，診断後速やかに適切な抗菌薬に変更すること が重要である。

Achromobacter xylosoxidans, a non-fermentative, multidrug-resistant, gram-negative bacterium that is widely distributed in the environment is known to cause nosocomial infections, such as bacteremia and pneumonia. However, A.xylosoxidans infections are usually reported in immunocompromised patients, and infection in healthy infants is rare. We report a case of A.xylosoxidans bacteremia in a 2-month-old male infant who presented with fever and a bad mood but no overt underlying disease. Blood test results showed a moderately elevated white blood cell count and serum C-reactive protein levels. Though physical examination did not show any inflammatory focus, we initiated intravenous ceftriaxone therapy against pneumococcus, Haemophilus influenzae, and group B streptococcus to treat suspected bacteremia. Blood cultures yielded A.xylosoxidans on the third day of admission, and therapy was switched from ceftriaxone to piperacillin/tazobactam and subsequently to piperacillin. The patient’s clinical symptoms gradually improved, and he was discharged on the 19 th day. His immunoglobulin levels and total complement activity were within the normal ranges; therefore, we did not suspect any humoral immunity abnormalities. However, the patient showed no overt underlying disease and the portal of pathogen entry was not identified; therefore, we monitored the patient’s course for any undiagnosed immunodeficiency. A.xylosoxidans is resistant to antimicrobial agents such as ampicillin, vancomycin, ceftriaxone, and cefotaxime, which are commonly used against severe bacterial infections in early infancy; therefore, it is necessary to switch to an appropriate antibiotic regimen immediately after diagnosis. Clinicians should be mindful of the possibility of A.xylosoxidans as a causative organism in cases of nosocomial bacteremia secondary to gram-negative rods in premature infants, and it is important to consider the possibility of A.xylosoxidans infection for selection of the optimal antibiotic until accurate identification of the causative agent.