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The following is a summary of “Early bacterial co-infections and ventilator-associated lower respiratory tract infections among intubated patients during the first and second COVID-19 waves: a European comparative cohort study,” published in the March 2025 issue of the Respiratory Research by Rouze et al.

The management of patients with critical illness suffering from severe SARS-CoV-2 pneumonia evolved over successive waves of the COVID-19 pandemic, influenced by logistical constraints and changes in clinical practice. This study aimed to compare the prevalence of early bacterial pulmonary co-infections and the incidence of ventilator-associated lower respiratory tract infections (VA-LRTI) between the first and second waves of the pandemic while also characterizing their microbiological profiles.

This investigation was part of a multicenter retrospective cohort study conducted across 35 European intensive care units (ICUs). The study included adult patients admitted for SARS-CoV-2 pneumonia who required invasive mechanical ventilation for at least 48 hours. Patients were consecutively enrolled from two time periods: February to May 2020 (period 1) and October 2020 to April 2021 (period 2). Bacterial co-infections were defined by positive respiratory or blood cultures, or a positive pneumococcal urinary antigen test, within 48 hours of intubation. VA-LRTI, comprising ventilator-associated tracheobronchitis (VAT) and ventilator-associated pneumonia (VAP), were diagnosed based on clinical, radiological, and quantitative microbiological criteria. The 28-day cumulative incidence of VA-LRTI was estimated using the Kalbfleisch and Prentice method, while statistical comparisons were made using multivariable logistic regression and Fine-and-Gray models.

A total of 1,154 patients were included, with 558 patients in period 1 and 596 in period 2. The prevalence of early bacterial pulmonary co-infections significantly increased from 9.7% in period 1 to 14.9% in period 2 (adjusted odds ratio [95% CI]: 1.52 [1.04–2.22], p = 0.03). Notably, Gram-positive cocci decreased from 59% to 48% of co-infections between the two periods. The overall incidence of VA-LRTI remained relatively stable, occurring in 50.4% of patients in period 1 and 53.9% in period 2 (adjusted sub-distribution HR: 1.14 [0.96–1.35], p = 0.11). However, a significant shift in VA-LRTI subtypes was observed, with VAP incidence increasing from 36% to 44.8% (adjusted sHR: 1.37 [1.12–1.66], p = 0.001), primarily occurring within the first 14 days post-intubation, while VAT incidence significantly declined from 14.3% to 9.1% (adjusted sHR: 0.61 [0.42–0.88], p = 0.007). 

The microbiological profile of VA-LRTI remained dominated by Gram-negative bacilli, with Pseudomonas aeruginosa, Enterobacter spp., and Klebsiella spp. accounting for 89% of infections in period 1 and 84% in period 2.

These findings highlight a significant increase in early bacterial pulmonary co-infections among intubated patients with COVID-19 during the second wave compared to the first. Although the overall incidence of VA-LRTI remained consistent, there was a notable shift in infection patterns, with VAP cases increasing while VAT cases declined. This shift underscores the need for continuous evaluation of infection control strategies and antimicrobial stewardship to mitigate the burden of bacterial complications in critically ill patients with COVID-19.

Source: respiratory-research.biomedcentral.com/articles/10.1186/s12931-025-03148-2