evidence: What really killed COVID-19 patients: It wasn't a cytokine storm, suggests study Secondary bacterial infection of the lung (pneumonia) was extremely common in patients with COVID-19, affecting almost half the patients who required support from mechanical ventilation. By applying machine learning to medical record data, scientists at Northwestern University Feinberg School of Medicine found that secondary bacterial pneumonia that does not resolve was a key driver of death in patients with COVID-19. It may even exceed death rates from the viral infection itself. [...] The investigators found nearly half of patients with COVID-19 develop a secondary ventilator-associated bacterial pneumonia.