Beneath the surface: a case report on nonencapsulated Streptococcus pneumoniae-associated invasive disease in an immunocompromised patient

Background. Streptococcus pneumoniae, a prominent human pathogen linked to various systemic diseases, includes non-typeable pneumococci marked by the absence of a detectable capsule. However, the majority of invasive infections are attributed to encapsulated strains. This case report details the first documented instance of invasive disease caused by non-typeable S. pneumoniae in Argentina since 2017. Case Presentation. A 19-year-old woman presented with haemorrhagic injuries attributed to chronic oral mucosa irritation. Subsequent hospitalization revealed bone marrow aplasia, leading to antibiotic, antifungal, antiviral, and immunosuppressive treatments, culminating in her discharge. Two weeks later, she was readmitted with sepsis related to a respiratory focus, exhibiting a negative COVID-PCR test. After ten days, ICU admission revealed additional infections: positive COVID-PCR test, fungal sinusitis, and S. pneumoniae bacteremia. Targeted treatments led to improvement, and the patient was subsequently discharged. S. pneumoniae characterization. Verification of the capsule’s absence utilized traditional methods such as the Quellung reaction, transmission electron microscopy, molecular assays, and Whole Genome Sequencing (WGS). The isolate, identified as ST18335, displayed genetic features and antibiotic resistance patterns, concordant between WGS and the agar dilution method. It demonstrated non-susceptibility to penicillin and cefotaxime, based on meningitis breakpoints, as well as meropenem and cotrimoxazole. Conclusion. This case underscores the clinical significance of non-typeable S. pneumoniae, emphasizing the necessity for a comprehensive approach to identification and characterization. The findings contribute to ongoing discussions regarding the challenges posed by non-typeable strains in vaccine development, understanding clinical impacts, and addressing antibiotic resistance. As the pneumococcal epidemiological landscape evolves, this case serves as a valuable addition to the evolving knowledge surrounding non-typeable S. pneumoniae, highlighting the continued need for surveillance and research in infectious diseases.

背景。肺炎链球菌是一种与多种全身性疾病相关的重要人类病原体，包括以无可见荚膜为特征的不可分型肺炎链球菌。然而，大多数侵袭性感染是由有荚膜菌株引起的。本病例报告详细介绍了自2017年以来阿根廷首例有记录的由不可分型肺炎链球菌引起的侵袭性疾病。 病例介绍。一名19岁女性因慢性口腔黏膜刺激导致出血性损伤就诊。随后住院发现骨髓再生障碍，进而接受了抗生素、抗真菌、抗病毒和免疫抑制治疗，最终出院。两周后，她因与呼吸道病灶相关的败血症再次入院，新冠病毒聚合酶链反应（COVID - PCR）检测呈阴性。十天后，入住重症监护病房（ICU）时发现又有其他感染：新冠病毒聚合酶链反应检测呈阳性、真菌性鼻窦炎以及肺炎链球菌菌血症。针对性治疗使病情有所改善，患者随后出院。 肺炎链球菌的特征描述。利用诸如荚膜肿胀试验、透射电子显微镜、分子检测以及全基因组测序（WGS）等传统方法验证了无荚膜情况。该分离株被鉴定为序列型18335（ST18335），其基因特征和抗生素耐药模式在全基因组测序和琼脂稀释法之间是一致的。根据脑膜炎折点，它对青霉素和头孢噻肟以及美罗培南和复方磺胺甲恶唑均显示不敏感。 结论。本病例强调了不可分型肺炎链球菌的临床重要性，强调了对其进行全面鉴定和特征描述的必要性。这些研究结果有助于正在进行的关于不可分型菌株在疫苗开发中所带来的挑战、了解临床影响以及应对抗生素耐药性的讨论。随着肺炎链球菌流行病学情况的演变，本病例为不断发展的关于不可分型肺炎链球菌的知识增添了有价值的内容，突出了在传染病方面持续监测和研究的必要性。