Introduction . During previous viral pandemics, reported co-infection rates and implicated pathogens have varied . In the 1918 influenza pandemic, a large proportion of severe illness and death was complicated by bacterial co-infection, predominantly Streptococcus pneumoniae and Staphylococcus aureus.Gap statement . A better understanding of the incidence of co-infection in patients with COVID-19 infection and the pathogens involved is necessary for effective antimicrobial stewardship.Aim . To describe the incidence and nature of co-infection in critically ill adults with COVID-19 infection in England.Methodology . A retrospective cohort study of adults with COVID-19 admitted to seven intensive care units (ICUs) in England up to 18 May 2020, was performed . Patients with completed ICU stays were included . The proportion and type of organisms were determined at <48 and> 48 h following hospital admission, corresponding to community and hospital-acquired co-infections.Results . Of 254 patients studied (median age 59 years (IQR 49-69); 64.6â% male), 139 clinically significant organisms were identified from 83 (32.7â %) patients . Bacterial co-infections/ co-colonisation were identified within 48 h of admission in 14 (5.5â %) patients; the commonest pathogens were Staphylococcus aureus (four patients) and Streptococcus pneumoniae (two patients). The proportion of pathogens detected increased with duration of ICU stay, consisting largely of Gram-negative bacteria, particularly Klebsiella pneumoniae and Escherichia coli . The co-infection/ co-colonisation rate> 48 h after admission was 27/1000 person-days (95â% CI 21.3-34.1). Patients with co-infections/ co-colonisation were more likely to die in ICU (crude OR 1.78,95â% CI 1.03-3.08, P=0.04) compared to those without co-infections/ co-colonisation.Conclusion . We found limited evidence for community-acquired bacterial co-infection in hospitalised adults with COVID-19, but a high rate of Gram-negative infection acquired during ICU stay.