Is it still too early to tell the effects of COVID-19?
COVID-19 is a new condition, therefore scientists are learning more each day about the long- and short-term effects it may have on the body. Professor Wendy Cooper is a pulmonary pathologist at NSW Health Pathology, Royal Prince Alfred Hospital in Sydney and explains that whilst the pattern of COVID-19 is similar to what is seen in patients with severe influenza, we still do not have enough data about the pathological effects to draw any conclusions.
“Most people with COVID-19 will experience mild symptoms such as a sore throat or cough and some might not experience symptoms at all. However, in a small percentage of people, the infection can be severe, and may require hospitalisation. When studying the lung tissue of those with severe disease under a microscope, we see an acute lung injury pattern called diffuse alveolar damage (DAD), which is caused by abnormal secretions in the lungs, preventing gas exchange.
“This pattern is not dissimilar to other severe respiratory illness such as severe influenza and Severe Acute Respiratory Syndrome (SARS). However, whilst many studies have been carried out on the clinical features of COVID-19, very few pathologic studies have been carried out on autopsies or biopsies, which has largely been due to infection control risk,” said Prof Cooper.
A recent paper published in the New England Journal of Medicine (NEJM) compared lungs obtained from patients who died from COVID-19 with lungs obtained during autopsy from patients who died from acute respiratory distress syndrome (ARDS) secondary to influenza A (H1N1) infection.
The paper showed that there are similar disease patterns in both end-stage COVID-19 and influenza, including diffuse alveolar damage, microthrombi and new blood vessel growth. However, it suggested that alveolar capillary microthrombi were nine times as prevalent in patients with COVID-19 as in patients with influenza.
“The study found that there were more blood clots within the small vessels of the COVID-19 infected lungs and proposed a significant difference. Whilst this is an interesting theory and may well be the case, I don’t think this has been proven. This particular study was quite weak due to a number of factors, including small sample size, differences in patient population and timing, i.e. how long they lived with the disease before they died and what ventilation they had received. I therefore don’t think there is enough evidence to make any firm conclusions.”
“COVID-19 may be different to other respiratory illnesses based on its epidemiology and clinical features, however, from what we know so far from a pathological perspective, the changes in the lungs are similar to what we see with an influenza of equivalent severity – it’s just that more people end up having severe disease with COVID-19.
“As there are more cases of COVID-19 in general, this could explain why we are seeing a higher number of complications, however until there is more data available, we cannot be sure,” said Prof Cooper.