化膿レンサ球菌はヒトの上気道と皮膚より分離されるグラム陽性球菌であり，伝染性膿痂疹や咽頭炎から壊死性筋膜炎などの致死性疾患まで様々な病態を軟組織に引き起こす．レンサ球菌は乳酸菌の一種であるとの考えが過去にあったように，レンサ球菌はエネルギー獲得において糖質の利用と発酵を好む．しかし，皮膚表層は化膿レンサ球菌の生態的ニッチであるが，エネルギー源となるグルコース等の糖質が少ない．本研究では，皮膚表面の低グルコース環境では，化膿レンサ球菌が皮膚組織中のフィラグリン分子由来のアルギニンを利用して病変を引き起こすことを示す．

Mycobacterium haemophilum is a non-tuberculous mycobacterium (NTM) that causes infections in immunocompromised patients and lymphadenitis in immunocompetent children. Currently, the appropriate antimicrobial regimen and duration of treatment for this infection has not been established. We managed a rare case of disseminated M. haemophilum infection in a post-renal transplant recipient, which was further exacerbated by immune reconstitution inflammatory syndrome (IRIS) during antimicrobial therapy. IRIS is known to occur during NTM therapy. Characteristically, cultures often yield negative results at the time of re-exacerbation, because it is an immunological reaction and cultures are obtained during treatment. Therefore, when a patient experiences another exacerbation during the treatment of M. haemophilum infection, IRIS should be considered as a potential differential diagnosis, and culture for acid-fast bacilli should be repeated.

A previous healthy, 58-year-old woman had a cat bite on the nail bed of her left thumb. A month later, she developed a low-grade fever, which persisted despite a 4-day course of cefteram prescribed at the previous center for upper respiratory symptoms. She was referred to our department on account of a left axillary swelling 59 days after the event. Contrast-enhanced CT revealed homogeneous lymphadenopathy in the left axilla, left neck, left supraclavicular fossa, and upper abdomen. A lymph node biopsy of the left axilla revealed the presence of pyogenic granulomatous lymphadenitis. Paired serum samples analyzed using immunofluorescence assay on Days 52 and 66 after the bite indicated a negative Bartonella henselae IgM titer of <20. However, the B. henselae IgG titer increased from a negative value of <64 to 256 on the respective date. Based on these findings, cat scratch disease (CSD) was diagnosed. A partial response to ibuprofen prompted the initiation of doxycycline therapy. The lymphadenopathy resolved after treatment over a 4-week period. However, she developed left eye discomfort associated with redness and swelling of the optic disc and peripapillary retinal edema without loss of visual acuity, which was first identified during the doxycycline therapy. Based on these findings, neuroretinitis was diagnosed. The ocular manifestations improved with continued antibiotic therapy without further recurrences after 2 months of follow-up.

Even with antibiotic therapy, CSD can manifest various ocular pathologies, including neuroretinitis and optic neuritis, which have no established treatment plan. In such cases, a personalized evaluation based on symptoms, course, and ocular findings is required.

An 86-year-old man suffered from COVID-19 and was treated at another hospital. He was transferred to our hospital due to hemoptysis and deterioration of respiratory condition. At our hospital, we treated with steroids and antibiotics and stopped the administration of cilostazol. His condition gradually improved. However, 24 days after onset of COVID-19 symptoms, he suffered a sudden pulmonary hemorrhage. Chest computed tomography showed a nodular shadow and ground glass opacities in the right lower and upper lobes, respectively. He was diagnosed with COVID-19-associated pulmonary aspergillosis (CAPA), following high serum antigen titer of Aspergillus and a positive sputum culture of Aspergillus fumigatus. Despite administration of antifungal drugs, he died 35 days after onset of COVID-19 symptoms.

Globally, CAPA has become a serious concern in the management of severe cases of COVID-19 due to its associated high mortality rate. However, the diagnosis of CAPA is challenging, because CAPA can occur in immunocompetent patients and radiological findings, such as cavitations suggesting fungal infection, are not often seen. In addition, mycological evidence is complicated by decreased use of diagnostic bronchoscopy, which is necessary to protect health-care workers from aerosol exposure. Hemoptysis may be helpful for the diagnosis of CAPA. In patients with COVID-19, hemoptysis should prompt consideration of the possibility of CAPA.