Now declared a pandemic by the World Health Organization (WHO), the majority of people who contract Covid-19 only experience mild and cold symptoms.
The WHO says around 80% of people with Covid-19 recover without the need for specialized treatment. Only one in six people fall seriously ill “and have difficulty breathing”.
So how can Covid-19 progress to a more serious disease with pneumonia, and what does it do to our lungs and the rest of our bodies?
How does the virus affect people?
Guardian Australia spoke with Professor John Wilson, President-elect of the Royal Australasian College of Physicians and respiratory physician.
He says that almost all of the serious consequences of Covid-19 translate into pneumonia.
Wilson says that people who catch Covid-19 can be classified into four main categories.
The least serious are those who are “subclinical” and who have the virus but have no symptoms.
Next are those who get an upper respiratory infection, which Wilson says “means a person has a fever and cough and perhaps milder symptoms like headache or conjunctivitis.”
He says, “People with minor symptoms are still capable of transmitting the virus but may not be aware of it. “
The largest group of those who test positive for Covid-19, and those most likely to come to hospitals and surgeries, are those who develop the same flu-like symptoms that would usually prevent them from working.
A fourth group, says Wilson, will develop a serious illness characterized by pneumonia.
He said, “In Wuhan, it turned out that among those who tested positive and sought medical help, about 6% had a serious illness.”
The WHO says that older people and people with underlying conditions like high blood pressure, heart and lung problems or diabetes are more likely to develop serious illness.
How does pneumonia develop?
When people with Covid-19 develop a cough and fever, Wilson says this is the result of the infection reaching the respiratory tree – the air passages that carry air between the lungs and outside .
He said, “The lining of the respiratory tree is injured, causing inflammation. In turn, this irritates the nerves in the lining of the airways. A small speck of dust can stimulate coughing.
“But if the situation gets worse, it goes beyond the lining of the airways and goes to the gas exchange units, which are at the end of the air passages.
“If they become infected, they respond by dumping inflammatory material into the air sacs in the back of our lungs.”
If the air sacs then become inflamed, Wilson says it causes an “outpouring of inflammatory material [fluid and inflammatory cells] in the lungs and we end up with pneumonia. “
He says the lungs that fill up with inflammatory materials are unable to supply enough oxygen to the bloodstream, which reduces the body’s ability to absorb oxygen and get rid of carbon dioxide.
“It is the usual cause of death from severe pneumonia,” he said.
How to treat pneumonia?
Professor Christine Jenkins, President of the Lung Foundation Australia and a prominent respiratory doctor, told Guardian Australia: “Unfortunately, so far, there is nothing that can prevent people from getting Covid-19 pneumonia.
“People are already testing all kinds of drugs and we hope to find out that there are different combinations of viral and antiviral drugs that could work. At the moment, there is no established treatment outside of supportive treatment, this is what we offer to people in intensive care.
“We ventilate them and maintain high oxygen levels until their lungs can function normally again when they recover.”
Wilson says patients with viral pneumonia are also at risk for developing secondary infections, so they would also be treated with antiviral drugs and antibiotics.
“In some situations, this is not enough,” he said of the current epidemic. “The pneumonia remained intact and the patients did not survive. “
Is Covid-19 pneumonia different?
Jenkins says that Covid-19 pneumonia is different from the most common cases for which people are admitted to hospital.
“Most of the types of pneumonia we know and admit to the hospital are bacterial and respond to an antibiotic.
Wilson says there is evidence that the pneumonia caused by Covid-19 can be particularly serious. Wilson says cases of coronavirus pneumonia usually affect all of the lungs, rather than small parts.
He says, “Once we have a lung infection and, if it relates to the air sacs, the body’s response is first to try to destroy [the virus] and limit its replication. “
But Wilson says this “first responder mechanism” may be compromised in certain groups, including people with underlying heart and lung disease, diabetes, and the elderly.
Jenkins says that, generally, people aged 65 and over are at risk of contracting pneumonia, as well as people with medical conditions such as diabetes, cancer or a chronic disease affecting the lungs, heart, kidneys or liver, smokers, native Australians and infants 12 months of age and under.
“Age is the main predictor of the risk of death from pneumonia. Pneumonia is still serious for an elderly person and, in fact, it was one of the leading causes of death in the elderly. Now we have very good treatments for pneumonia.
“It’s important to remember that no matter what your health and activity, your risk of getting pneumonia increases with age. Indeed, our immune system naturally weakens with age, which makes it more difficult for our body to fight against infections and diseases. “
- Due to the unprecedented and continuing nature of the coronavirus epidemic, this article is regularly updated to ensure that it best reflects the current situation. All major corrections to this version or to previous versions of the article will continue to be noted in accordance with Guardian editorial policy.