There has been much written about how to protect yourself from catching the new coronavirus but far less on what it does to those who catch it.
Yet doctors are learning more about the disease every day as cases mount and detailed reports are starting to appear in medical journals across the world. They describe a wide spectrum of illness ranging from cases that are so mild the patient does not notice, to those where patients decline at pace and die within a week.
Data currently suggest that around 80 per cent of confirmed Covid-19 cases are mild, 15 per cent are severe and five per cent are critical. Over time it is likely that mild cases will grow as a proportion of the total, as more asymptomatic cases are picked up through community testing.
Everyone, no matter their age, is susceptible to catching the virus and passing it on to others - although early figures suggest the "risk of severe illness, disease and death" increases markedly in people aged over 60 and in people with underlying conditions.
But while illness is less common and usually less severe in younger adults, the UK Government warns that they are not immune. "Children can be infected and can have a severe illness", it says.
The following case studies have been adapted from published medical reports and give a good idea of the different types of illness doctors across the world are seeing:
Case 1: Mild Female, age 35
On January 20, a passenger disembarked from the Diamond Princes cruise ship in Hong Kong. Just 10 days later, on February 1, they tested positive for Covid-19.
By then the ship had sailed on and was docked in Yokohama, Japan. As news of the positive test spread, the Diamond Princess was quarantined and its passengers told to isolate themselves in their cabins.
All on board were provided with thermometers and asked to check their temperature several times a day. Crew members were instructed to continue their duties and to report any fever or respiratory symptoms.
Despite the lockdown, the virus spread fast. By February 28, a total of 705 Covid-19 cases were confirmed among 4,061 passengers and crew; 392 cases were symptomatic, 36 people were taken to intensive care units, and six patients died. A seventh death was announced yesterday.
Case 1 occurred in a 35-year-old woman from South Asia who worked as a waitress on the ship. On day one of her illness, February 7, she experienced throat dryness and a slight cough. She and her room-mate shared a bathroom with two others who had previously had similar symptoms. Case 1 reported her symptoms but continued to work. On Day 3, she had throat soreness, stayed in her room, and was tested for the virus.
On Days 4 and 5, her symptoms diminished but on Day 6, her test came back positive and she was transferred from the ship to Asahi General Hospital in Chiba, 40 miles away, on the other side of Tokyo Bay. When admitted, she had a "slight sore throat and cough" but all her vital signs were normal. On examination, doctors found her throat was "bright red" but there were no lesions or pus and she did not have pneumonia.
However, her throat was sore and she continued to cough. On Day 8, she reported "slight rhinorrhea" - a runny nose.
On Day 9, she again tested positive but her symptoms continued to diminish, and by Day 10 she was feeling fine. Test results were positive on Days 13 and 15, negative on Day 19, positive again on Day 20, and negative on Days 22 and 23 - meeting the criteria for her safe discharge from hospital.
Case 1 never had a fever or shortness of breath. Her only symptoms were a sore throat and a cough.
One of her colleagues, a kitchen porter on the same ship, had the same bright red throat but in the later days of his illness could not feel it, even when testing positive.
"As the virus spreads, more mild Covid-19 cases are likely, and clinicians should be aware of clinical manifestations in the absence of severe symptoms," say the report's authors.
Case 2: Mild 10 children, aged three months to 11 years
Ten children with confirmed Covid-19 infections were admitted to the Children's Hospital in Shanghai, China, between January 19 and February 3.
Their ages ranged from three months to 11 years old. All were linked to known adult cases or epidemic hotspots and all were suffering "acute fever and or respiratory symptoms" at the time of their admissions to hospital.Seven of the children had been exposed to the virus in their homes and one is thought to have been infected when travelling on a bus with two adults from Wuhan.
The researchers note that the three-month-old infant may have passed the virus on to her parents rather than the other way round. Her parents developed symptomatic Covid-19 seven days after they looked after her "without protective measures".
Say the authors: "Personal medical protection is crucial when care providers look after the infected child." The children's symptoms varied. Eight had a temperature, six had a cough, four had sore throats, three had a stuffy nose and two had sneezing and runny noses. None of the patients had difficulty breathing but chest X-rays revealed four had mild pneumonia.
Samples taken from the children also suggested the virus may be spread through faeces. Six had faecal samples tested for Covid-19 and five (83.3 per cent) were positive.
All 10 children "recovered uneventfully" within two to three weeks and all were discharged from hospital.
However, the authors warn: "Prolonged virus shedding is observed in respiratory tract and faeces at the convalescent stage."
Case 3: Severe Male, 35
On January 19, a 35-year-old man wearing a face mask entered an urgent healthcare facility in Snohomish County, Washington state, just north of Seattle.
Just back from visiting relatives in Wuhan, China, he had been feverish and coughing for several days. Doctors were swift to act. They notified state officials, who in turn alerted the federal Emergency Operations Centre in Atlanta. Nose and throat swabs were taken and sent for analysis. The man was initially taken home and isolated.
The following day the tests came back positive: it was the first of a rapidly rising number of Covid-19 cases to be diagnosed on American soil and the first indication that Washington state would become an epidemic hotspot. The US now has more than 300 confirmed cases.
On admission, the patient reported a "persistent dry cough" and a two-day history of nausea and vomiting. His mucus membranes were found to be dry but he had no shortness of breath or chest pain. "His vital signs were within normal ranges".
For the next three days (Days 6 to 9 of his illness) he remained "largely stable" in a specialist hospital isolation unit. His cough continued, he had intermittent fever and several loose bowel movements.
Doctors noted that he "appeared fatigued". Apart from hypertriglyceridemia - a common precursor to heart disease - the patient was a healthy non-smoker. At just 35, he was also young. Yet his condition started to deteriorate.
On the night of his ninth day of illness, an X-ray showed evidence of pneumonia in the lower left lobe of his left lung. This "coincided with a change in respiratory status", with his oxygen saturation levels dropping sharply from 96 to 90 per cent.
Now on supplemental oxygen and apparently on a downward slope, the patient was diagnosed with "severe pneumonia" on Day 10 when new chest radiographs showed that the virus had spread to both his lungs.
Doctors were concerned enough to administer an experimental antiviral called remdesivir, which was first developed to combat Ebola and is now being more widely tested in the US and China as a treatment for coronavirus.
Two days later the patient's condition started to improve. Twelve days after first falling ill and after eight days in hospital, he was able to breathe properly without oxygen and his lungs had cleared. "His appetite improved, and he was asymptomatic aside from intermittent dry cough and rhinorrhea [runny nose]," noted the hospital.
Case 4: Fatal Male, 50
A 50-year-old man was sent to a fever clinic in Beijing on January 21 with symptoms of fever, chills, cough, fatigue and shortness of breath. He had been in Wuhan between January 8 and 12, and told doctors he first noticed symptoms of "mild chills and dry cough" on January 14. But rather than immediately seek medical help, he kept working for another week.
Chest X-rays revealed multiple patchy shadows in both lungs and tests showed he had Covid-19. He was immediately taken to an isolation ward and received supplemental oxygen via a face mask.
After receiving medication, including antivirals and antibiotics, his body temperature reduced from 39C (102.2F) to 36.4C. However, his cough, breathlessness and fatigue persisted.
On Day 12 of his illness, his breathing became more laboured but he refused ventilator support in the intensive care unit repeatedly because he suffered from claustrophobia.
Then, in the afternoon of Day 14, his blood oxygen levels and shortness of breath worsened.
Despite receiving high flow oxygen therapy, the oxygen saturation levels in his blood dropped to 60 per cent, and the patient had a "sudden cardiac arrest".
He was immediately given invasive ventilation, chest compression, and adrenalin but could not be resuscitated.He died at 6.31pm (Beijing time) on Jan 27.
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