Streptococcus pyogenes, commonly referred to as Group A Streptococcus (GAS), has the ability to induce a diverse range of illnesses.

In several European countries and the United States, a notable surge in invasive GAS (iGAS) infections has been documented since mid-2022. This sharp increase contrasts with the gradual rise in iGAS incidence observed among children over the past three decades. As demonstrated for several viral infections, the recent upturn in iGAS infections is potentially linked to the relaxation of mitigation measures implemented during the COVID-19 pandemic, such as face mask usage and school closures.

Since November 2022, concerns have been raised by French public health authorities regarding the rise in levels of iGAS infections, and an unexpected increase in pediatric severe GAS infections was reported in a French single-center study. However, this study ended in December 2022 and could only explore short-term trends. The Necker - Enfants malades Hospital in Paris, France, represents an excellent opportunity to examine the impact of the COVID-19 pandemic and the associated non-pharmaceutical interventions on the incidence of severe GAS infections, during, and after the pandemic.

This study aims to investigate trends of severe GAS infection incidence in children in the Paris area over the course of the COVID-19 pandemic.

Streptococcus pyogenes, commonly referred to as Group A Streptococcus (GAS), has the ability to induce a diverse range of illnesses. In primary care, acute pharyngitis, commonly known as 'strep throat', is the predominant form of GAS infection. Other commonly encountered non-invasive GAS infections encompass impetigo, scarlet fever, perianal infections, and paronychia. GAS may also cause rarer yet severe conditions such as streptococcal toxic shock syndrome, pneumonia with pleural empyema, and septic shock; most severe GAS infections can even be life-threatening.

In several European countries and the United States, a notable surge in invasive GAS (iGAS) infections has been documented since mid-2022. This sharp increase contrasts with the gradual rise in iGAS incidence observed among children over the past three decades. As demonstrated for several viral infections, the recent upturn in iGAS infections is potentially linked to the relaxation of mitigation measures implemented during the COVID-19 pandemic, such as face mask usage and school closures. Non-pharmaceutical interventions and behavioral changes during the COVID-19 pandemic modified the spread of SARS-CoV-2 and several respiratory pathogens, including GAS. Reduced exposure to endemic infectious agents may have created an immunity gap, leading to unexpected epidemics of viral and bacterial infections after non-pharmaceutical interventions were relaxed.

Since November 2022, concerns have been raised by French public health authorities regarding the rise in levels of iGAS infections, and an unexpected increase in pediatric severe GAS infections was reported in a French single-center study. However, this study ended in December 2022 and could only explore short-term trends. The Necker - Enfants malades Hospital in Paris, France, represents an excellent opportunity to examine the impact of the COVID-19 pandemic and the associated non-pharmaceutical interventions on the incidence of severe GAS infections, during, and after the pandemic. This tertiary care university hospital is located in a densely populated region and has various specialized departments involved in the management of severe infections, including pediatric intensive care units (PICU), orthopedics, pulmonology, otolaryngology, dermatology, infectious diseases, and microbiology.

This study aims to investigate trends of severe GAS infection incidence in children in the Paris area over the course of the COVID-19 pandemic.

Inclusion Criteria:

• Children under the age of 18 years.
• Admitted to Necker-Enfants Malades hospital for community-acquired or healthcare-associated severe Group A Streptococcus (GAS) infections between January 1, 2018, and December 31, 2023.
• Severe GAS infections comprises "invasive" and "probable invasive" GAS illnesses.

"Invasive" GAS infection will be defined as:

• isolation by culture or polymerase chain reaction (PCR) of GAS from a normally sterile site (e.g., blood, pleural fluid, cerebrospinal fluid, joint fluid, bone, bronchoalveolar lavage fluid); or
• isolation of GAS from a sterile or non-sterile site accompanied by necrotizing fasciitis or streptococcal toxic shock syndrome.

"Probable invasive" GAS will be defined as acute infections with GAS isolated from a non-sterile site, which includes sputum, otorhinolaryngology surgical specimens (mastoiditis, ethmoiditis, pharyngeal abscess) accompanied with one or more of the following severity criteria:

• intravenous (IV) antibiotics;
• surgery; and/or
• admission to the PICU.

Exclusion Criteria:

• Non-severe GAS infection, such as acute otitis media with otorrhea, pharyngitis, scarlet fever, GAS skin carriage.
• GAS identified on minor/superficial skin lesions.
• Otolaryngology infections (e.g., parapharyngeal abscess) that do not require IV antibiotics, surgery, or PICU admission.
• Opposition to the use of routine data.

All consecutive children under the age of 18 years with community-acquired or healthcare-associated severe Group A Streptococcus (GAS) infections admitted to Necker-Enfants Malades hospital between January 1, 2018, and December 31, 2023.