A buildup of SARS-CoV-2, the virus causing Covid-19, in the lungs is likely behind the steep mortality rates seen in people with the infectious disease, finds a new study.
The findings, published in the journal Nature Microbiology, showed that people, who died of Covid-19, had, on average, 10 times the amount of virus, or viral load, in their lower airways as did severely-ill patients who survived their illness.
The results contrast with previous suspicions that simultaneous infections, such as bacterial pneumonia or overreaction of the body's immune defense system, played major roles in heightened risk of death, said researchers at New York University- Grossman School of Medicine.
Meanwhile, the team found no evidence implicating a secondary bacterial infection as the cause of the deaths, although they cautioned that this may be due to the frequent course of antibiotics given to critically-ill patients.
"Our findings suggest that the body's failure to cope with the large numbers of virus infecting the lungs is largely responsible for Covid-19 deaths in the pandemic," said lead author Imran Sulaiman, Professor in the Department of Medicine at NYU Langone Health.
Further, the study revealed that those who died had, on average, 50 per cent lower production of a type of immune chemical that targets the coronavirus, compared with the Covid-19 patients who survived the illness.
These customised proteins are part of the body's adaptive immune system, a subset of cells and chemicals that "remember" invading newly-encountered microbes, leaving the body better prepared for future exposure, the team said.
"These results suggest that a problem with the adaptive immune system is preventing it from effectively combating the coronavirus," said Leopoldo Segal, Associate Professor in the Department of Medicine at NYU Langone.
"If we can identify the source of this issue, we may be able to find an effective treatment that works by bolstering the body's own defences," Segal added.
However, he cautioned that the team only studied coronavirus patients who survived their first two weeks of hospitalisation. It is possible, Segal said, that bacterial infections or autoimmune reactions may play a greater role in Covid-19 mortality that occurs earlier.
For the research, the team collected bacterial and fungal samples from the lungs of 589 men and women who were hospitalised.