To determine the prevalence and microbiological characteristics of bacterial coinfection at hospital admission, assess its association with adverse outcomes, and evaluate the diagnostic performance of admission procalcitonin (PCT) relative to other inflammatory biomarkers.
Approach:
Study Design: Post hoc analysis of a prospective longitudinal cohort at a single hospital in Spain.
Patient Population: Included 2187 consecutive adults hospitalized primarily for clinically significant COVID-19 from March 1, 2020, through July 31, 2022, who had PCT measured within 48 hours of admission.
Data Collection: Admission data included demographics, comorbidity burden, COVID-19 severity, clinical outcomes, and inflammatory biomarker levels.
Microbiological Investigation: Testing was performed according to predefined criteria in patients with severe disease, compatible radiographic findings, or suspected bacterial infection. Microbiological confirmation was the reference standard.
Key Findings:
Bacterial coinfection within 48 hours of admission occurred in 50 patients (2.3%). The respiratory tract was the most frequent source, and *Streptococcus pneumoniae* was the predominant pathogen.
Coinfection was independently associated with intensive care unit admission, invasive mechanical ventilation, or 28-day mortality (adjusted odds ratio, 4.31).
PCT provided the highest discrimination among evaluated biomarkers (area under the curve, 0.79). At PCT levels below 0.5 ng/mL, the negative predictive value was 99.1%, supporting its use primarily as a rule-out biomarker.
Limitations:
Although data collection was prospective, the post hoc analysis may be subject to residual confounding.
Microbiological testing was not uniform, potentially introducing partial-verification bias and underestimating coinfection.
Limited respiratory cultures, inclusion of clinically significant nonrespiratory infections, and the single-center design may affect interpretation and generalizability.
Conclusion:
Bacterial coinfection at admission was uncommon but associated with worse outcomes. Admission PCT demonstrated good discrimination and strong rule-out capacity, potentially supporting early antibiotic decisions and antimicrobial stewardship.
