What the science tells us about how COVID-19 spreads, sickens and kills

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It’s been three months since vendors in a market in Wuhan, China, began showing symptoms of a debilitating respiratory illness.

Since then, the virus has been identified and the disease named: COVID-19. It’s gone on to sicken over 100,000 people and kill over 3,500 people, including in Washington state.

What does the science say about COVID-19?

Medical reports prepared by the World Health Organization on the outbreak in China and another published on the first known U.S. case offer glimpses into the scientific nature of the new coronavirus and the disease it causes.

The goal of the report of the WHO-China Joint Mission on Coronavirus Disease 2019 (COVID-19) was to provide a rapid assessment of the disease and help combat it.

The joint mission consisted of 25 international experts from a variety of professions.

What’s killing COVID-19 patients?

The report contains a detailed post-mortem examination of a 50-year-old man.

In that case, COVID-19 resulted in acute respiratory distress syndrome.

According to Dr. Peter McGough, medical director for UW’s Neighborhood Clinics, the report indicates the man died after his lungs became inflamed and damage occurred to the alveoli — the air sacs that take up oxygen and transfer it to the blood stream.

The man also had damage to the lining of his lungs and fluid retention. That results in a lack of oxygen reaching the brain and heart, resulting in death.

While the virus is new, its attack on the body isn’t that unusual, McGough said.

“It’s not that different from the flu,” McGough said.

Whether a patient recovers or dies depends on many factors, McGough said. If the patient has impaired lung function caused by asthma or COPD, for example, they will be at a disadvantage. An impaired immune condition, diabetes and other factors also increase the chances for a more severe impact.

“There are some nice surprises,” McGough said. “We are not seeing severe cases in children. Though, that can change.”

Demographics and Transmission

Out of nearly 56,000 cases reviewed in the WHO report, the median age of victims was 51. The majority of cases are aged 30-69. Slightly more were men than women. The reports authors speculated that could be because more men suffer from chronic illness and smoke.

In China, the disease is largely being transmitted in families. It’s spread via droplets and on items like clothing, furniture and other surfaces during close, unprotected contact between an infector and infectee. Airborne spread has not been reported for COVID-19, according to the WHO report, and it is not believed to be a major driver of transmission.

Transmission to health care workers “does not appear to be a major transmission feature of COVID-19 in China,” according to the report.

Higher rates of transmission were seen in Chinese long-term care facilities. They also were noted in prisons and hospital patients. In Washington state, the highest numbers of deaths and concentrated illnesses came from a Kirkland care facility.

Immunity and risk

Researchers in China could find no pre-existing immunity in people. “...everyone is assumed to be susceptible,” the report said.

It’s still too early to tell if a person can get the disease again after an initial infection. Typically, viral infections lead to an immunity. However, viruses can mutate, and a patient might not have immunity to a different strain.

The WHO report pegged people aged 60 and over to be the highest risk for severe disease and death. Also in that group are people with underlying conditions.

Children seem to have an advantage. COVID-19 is rare and mild when it does occur in children in China. Approximately 2.4 percent of the total reported cases were people aged under 19 years.

How illness presented itself in first US case

How will you know if you have the novel coronavirus, COVID-19, and not, say a bad case of the flu?

Symptoms can be similar to other respiratory infections or as mild as a common cold.

According to the CDC’s testing guidelines, “Most patients with confirmed COVID-19 have developed fever and/or symptoms of acute respiratory illness.”

A review of the New England Journal of Medicine’s recent report on the first U.S. case offers insight only in what that individual, a 35-year old Snohomish County resident, experienced.

The case study was released to educate physicians and the general public Jan. 31 on what was known so far:

“This case highlights the importance of close coordination between clinicians and public health authorities at the local, state and federal levels, as well as the need for rapid dissemination of clinical information related to the care of patients with this emerging infection.”

According to the report:

The patient had returned from a visit to Wuhan, China to see family. He checked in Jan. 19 to an urgent care clinic in Snohomish County.

He had been suffering for four days with a cough and fever. Other than a history of high triglycerides, he had no other chronic health issues. Staff at the urgent care clinic ordered home isolation and monitoring by the local health department.

One day later, testing showed he had COVID-19. He then was sent to Providence Regional Medical Center for clinical observation “with health care workers following CDC recommendations for contact, droplet, and airborne precautions with eye protection.”

“On admission, the patient reported persistent dry cough and a 2-day history of nausea and vomiting; he reported that he had no shortness of breath or chest pain,” according to the report.

The next few days, his vital signs were stable, but he experienced “intermittent” fevers with periods of elevated heart rate, along with a nonproductive cough.

According to the report, he was given acetaminophen every four hours and ibuprofen every six hours, along with cough medication and saline for hydration.

Day 5 in the hospital, he showed signs of pneumonia in a part of his left lung. Day 6, he was put on supplemental oxygen.

“Given the changing clinical presentation and concern about hospital-acquired pneumonia,” a round of antibiotics was started.

By Day 7 in the hospital he was put on “investigational” antiviral therapy, remdesivir, just for that evening. The National Institutes of Health reported Feb. 25 that there is a randomized, controlled clinical trial to evaluate safety and efficacy of the drug in treating COVID-19 at the University of Nebraska in Omaha, limited to hospitalized patients diagnosed with COVID-19.

The next day, the man’s condition improved.

He eventually recovered and has since been released.

Symptoms, disease progression and severity

Most people infected with COVID-19 virus have mild disease and recover, according to the WHO report. Approximately 80 percent of confirmed patients have mild to moderate disease.

Symptoms of COVID-19 can range from none to severe pneumonia and death.

According to data from more than 55,000 cases, typical signs and symptoms include: fever (87 percent of patients), dry cough (67 percent), fatigue (38 percent), sputum production (33 percent), shortness of breath (18 percent), sore throat (13 percent), headache (13 percent), muscle pain (14 percent) and chills (11 percent).

People with COVID-19 generally develop symptoms on an average of 5-6 days after infection.

The proportion of asymptomatic infections couldn’t be determined but they appear to be relatively rare, according to the report.

Recovery

It took patients about two weeks to recover after symptoms first appeared, according to the WHO report. Patients with severe or critical disease took three to six weeks.

Preliminary data suggested that severe cases developed one week after symptoms first appeared.

The report noted that by February, the survival rate in China was increasing. Early detection, identification and treatment were cited as factors.