[Impact of the first year of the COVID-19 pandemic on the epidemiology of invasive infections (bacteremia) in the hospitals of the Assistance Publique-Hôpitaux de Paris].

Introduction: The COVID-19 pandemic has led to a massive influx of patients suffering from severe forms of the disease into hospitals, often requiring intensive care (vascular catheters, ventilation, etc.) which exposes them to high risks of nosocomial infections, particularly invasive infections (bacteremia).

Method: The impact of the COVID-19 pandemic on the epidemiology of bacteremia in 2020 was analysed in 25 hospitals of the Assistance Publique-Hôpitaux de Paris (AP-HP, approximately 14,000 beds, covering the Île-de-France region). Up to a quarter of patients admitted to AP-HP during the March-April period (peak of the 1st wave) were infected with COVID-19. The incidence over 100 admissions of bacteraemia increased overall compared to previous years: by 24% in March 2020 and by 115% in April.

Results: The evolution of the incidence of bacteremia was not the same for 2 groups of microorganisms with very different ecologies. For the "hospital" type microorganisms classically responsible for nosocomial infections, the incidence increased significantly in March-April 2020: (×2.3), (×2.4), (×2.4), (×3.4), yeasts (×2.7). Two thirds of the bacteremias caused by these microorganisms were considered as acquired during hospitalization. Importantly, there was also a sharp increase in the incidence of bacteremia caused by antibiotic-resistant strains. The antibiotics used as indicators were the 3rd generation cephalosporins (3GCs), major antibiotics in the treatment of serious infections used for monitoring bacterial resistance in Europe. For example, the incidence of bacteremia with 3GC-resistant strains increased threefold in April 2020 for . During the same period, the consumption of 3GC increased sharply in the same hospitals (+131% in March and +148% in April). For (pneumococcus) and (group A hemolytic streptococcus), two pathogens responsible for mainly community and respiratory-transmitted infections, the pandemic had the opposite effect. There was a decrease in incidence in 2020 by 34% and 28% respectively for these two species, particularly in the spring when strict containment, physical distancing and mask-wearing measures were in place. A slight re-emergence of infections with these two species occurred in the summer of 2020 after the relaxation of prevention measures. In contrast to what was seen above, 4/5 of the bacteremias caused by these two species were considered as community-acquired.

Conclusion: The COVID-19 pandemic which had a strong impact on hospital management and social organization in the general population, had opposite impacts on the incidence of bacteremia depending on the pathogens and their mode of transmission.