It was not a “cytokine storm” so often believed to cause mortality due to Covid-19, a team of US scientists have argued, but secondary bacterial pneumonia that does not resolve was a key driver of death in patients with the infection.
They found that 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. It may even exceed death rates from the SARS-CoV-2 viral infection itself, they said in a study published in the Journal of Clinical Investigation.
By applying machine learning, a form of artificial intelligence (AI), to medical record data, scientists at Northwestern University Feinberg School of Medicine in the US found evidence that Covid-19 does not cause a “cytokine storm,” severe immune reaction in which the body releases too many cytokines into the blood too quickly.
Cytokines play an important role in normal immune responses, but having a large amount of them released in the body all at once can be harmful. “Our study highlights the importance of preventing, looking for and aggressively treating secondary bacterial pneumonia in critically ill patients with severe pneumonia, including those with Covid-19,” said study senior author Benjamin Singer, an associate professor at Northwestern University Feinberg School of Medicine, US.
“Those who were cured of their secondary pneumonia were likely to live, while those whose pneumonia did not resolve were more likely to die,” Singer said in a statement.
“Our data suggested that the mortality related to the virus itself is relatively low, but other things that happen during the ICU stay, like secondary bacterial pneumonia, offset that,” he added. The findings also negate the cytokine storm theory, said Singer.
“The term ‘cytokine storm’ means an overwhelming inflammation that drives organ failure in your lungs, your kidneys, your brain and other organs,” Singer said. “If that were true, if cytokine storm were underlying the long length of stay we see in patients with Covid-19, we would expect to see frequent transitions to states that are characterized by multi-organ failure. That’s not what we saw,” he added.