Bacterial and Viral Co-Infections in COVID-19 Patients: Etiology and Clinical Impact

Background: Mixed infections can worsen disease symptoms. This study investigated the impact of mixed infections with viral and bacterial pathogens in patients positive for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Methods: Using the in-house multiplex PCR method, we tested 337 SARS-CoV-2 positive samples for co-infections with three bacterial and 14 other viral pathogens. Results: Between August 2021 and May 2022, 8% of 337 SARS-CoV-2-positive patients had bacterial co-infections, 5.6% had viral co-infections, and 1.4% had triple mixed infections. The most common causes of mixed infections were <i>Haemophilus influenzae</i> (5.93%) and respiratory syncytial virus (RSV) (1.18%). Children < 5 years old had more frequent co-infections than adults < 65 years old (20.8% vs. 16.4%), while adults showed a more severe clinical picture with a higher C-reactive protein (CRP) level (78.1 vs.16.2 mg/L; <i>p</i> = 0.033), a lower oxygen saturation (SpO2) (89.5 vs. 93.2%), and a longer hospital stay (8.1 vs. 3.1 days; <i>p</i> = 0.025) (mean levels). The risk of a fatal outcome was 41% in unvaccinated patients (<i>p</i> = 0.713), which increased by 2.66% with co-infection with two pathogens (<i>p</i> = 0.342) and by 26% with three pathogens (<i>p</i> = 0.005). Additionally, 50% of intensive care unit (ICU) patients had a triple infection, compared with only 1.3% in the inpatient unit (<i>p</i> = 0.0029). The risk of death and/or ICU admission was 12 times higher (<i>p</i> = 0.042) with an additional pathogen and increased by 95% (<i>p</i> = 0.003) with a third concomitant pathogen. Conclusions: Regular multiplex testing is important for prompt treatment and targeted antibiotic use.