Community-acquired pneumonia (CAP) remains a significant global health concern, particularly among the pediatric population. Annually, approximately 1400 per 100 000 children experience CAP, with the highest incidence observed in those under the age of 5 [1].

Complicated CAP occurs in approximately 2-12% of all children with pneumonia and up to 30% of those requiring hospitalization [2], [3], [4]. In severe course, pneumonia patients may develop pleural effusion/empyema, necrotizing pneumonia (NP), bronchopulmonary fistula or lung abscess [5]. Among these, complicated parapneumonic effusion and pleural empyema are the most common, and NP the most severe form of pleuropulmonary complication [6], [7], [8]. The predominant causative agent of complicated CAP in children is Streptococcus pneumoniae [5], [9]. Other common pathogens include Staphylococcus aureus, Streptococcus pyogenes (group A Streptococcus, GAS), Staphylococcus epidermidis, and Mycoplasma pneumoniae [8], [10], [11].

Following the introduction of 7-valent pneumococcal conjugate vaccines (PCVs), a significant reduction in the overall hospitalizations due to bacterial pneumonia was reported [12]. Simultaneously, the incidence of complicated pneumonia has surprisingly increased [13], [14], [15]. After the implementation of the broader spectrum 10- and 13-valent PCVs an interim decrease in the incidence of complicated CAP cases was observed [16], [17], [18]. However, this was not an ubiquitous phenomenon, as some countries reported further increases in complicated pneumonia [16], [18].

COVID-19 pandemic had a profound impact on the epidemiology of pediatric acute respiratory infections including pneumonia. Due to epidemiological restrictions, a marked reduction in the number of respiratory infections was noted in the early phase of the pandemic resulting in a reduced pathogen circulation. This however, led to increased population susceptibility and subsequent resurgence of infections once the restrictions were lifted [19]. In particular, the immediate post-pandemic period was marked by unexpectedly high notifications of GAS infections [20]. In 2022 many countries reported a substantial increase in the incidence of GAS infections, mainly affecting children under 10 years of age [21], [22], [23], [24], [25]. While most cases were mild illnesses such as tonsillitis, pharyngitis, impetigo, cellulitis and scarlet fever, invasive GAS encompassing bacteremia, intracranial infections, as well as bone and joint infections were also increasingly noted [21], [22], [23], [24], [25], [26]. In the context of the current GAS outbreak, lower respiratory tract infections including pneumonia were reported in single studies, and data on pleuropulmonary complications are scarce [21], [22], [26], [27].

Therefore, our objective was to analyze the etiology and clinical presentation of complicated CAP cases in the infectious season 2022/2023 with a particular focus on infections caused by GAS.