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

## TL;DR

This case report describes the first documented invasive disease caused by non-typeable Streptococcus pneumoniae in Argentina, highlighting its clinical and research implications.

## Contribution

The first documented case of invasive disease caused by non-typeable S. pneumoniae in Argentina since 2017.

## Key findings

- Non-typeable S. pneumoniae isolate ST18335 was confirmed using multiple methods including WGS.
- The isolate showed resistance to several antibiotics, including penicillin and cefotaxime.
- The case highlights the importance of surveillance and research for non-typeable pneumococci.

## Abstract

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.

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.

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.

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.