Covid-19 – What Is Known And What Is Unknown

The case fatality rate dropped to 0.7% for those with symptom onset after Feb 1.

Covid-19 has held global attention for about two months. Its impact has been personal, economic and social. According to the World Health Organization’s (WHO) situation report dated 3 March 2020, there were 90,870 confirmed cases globally of which 80,304 were in China and 10,566 outside China in 72 countries; with 2,946 deaths in China and 166 outside China.

There is much that is known about the outbreak of the new infection, which was reported to WHO by China on 30 December 2019, but there is much more that is still unknown.

The WHO sent a mission to China comprising 25 national and international experts with the objectives to enhance understanding of the Covid-19 outbreak, to share knowledge, to generate recommendations and to establish priorities for collaboration and research to address critical gaps in knowledge, response, readiness tools and activities.

The report of the WHO-China joint mission on Covid-19 16-24 February 2020 was published on 28 February 2020. The mission analysed data from 55,924 laboratory confirmed cases as of 20 February 2020. A summary of the salient findings for public information is found below.

What is known

The median age of those infected was 51 years with a range from 2 days to 100 years old. The majority (77.8 per cent) of the infected were aged between 30-69 years of which 51.1 per cent were males, 77.0 per cent from Hubei province and 21.6p er cent were farmers or labourers. Data on those below 18 years suggested they had a low attack rate (2.4 per cent of all reported cases).

Covid-19 is transmitted by droplets and fomites (objects likely to carry the virus like door knobs, furniture, clothes, utensils) during close unprotected contact between the infected person and an uninfected person.

Airborne spread has not been reported and is not believed to be a major driver of transmission currently; however, it could occur if certain aerosol generating procedures are carried out in health care facilities.

Viable virus has been identified in the faeces of some patients. The faecal-oral route does not appear to be a driver of transmission; however, its role is yet to be determined.

The human-to-human transmission in China has largely been occurring in families. Of the clusters in Guangdong and Sichuan provinces, 75-85 per cent were in families. Preliminary studies in Guangdong estimate the secondary attack rate in households range from 3-10 per cent.

Transmission were reported in health care stings, prisons and other long-term living facilities. The role of the settings and groups in transmission were unclear although the close proximity and contact, and environmental contamination were factors that could amplify transmission. However, they did not appear to be major drivers of transmission.

There were 2,055 cases reported among health care workers (“HCW”) in 476 hospitals across China, as of 20 February 2020, with the majority (88 per cent) of the cases in Hubei, with 12 per cent outside Hubei.

The exposure in the latter was reported in most cases to have been traced back to a confirmed case in a household — transmission within health care settings did not appear to be a major transmission driver.

There is no known pre-existing immunity in humans as Covid-19 is a newly identified infection. Everyone is assumed susceptible although some may have risk factors that increase susceptibility to infection.

The symptoms are non-specific with the presentation ranging from no symptoms (“asymptomatic) to sever pneumonia and death. The typical signs and symptoms in the cases analysed included: fever (87.9 per cent), dry cough (67.7 per cent), fatigue (38.1 per cent), sputum production (33.4 per cent), shortness of breath (18.6 per cent), sore throat (13.9 per cent), headache (13.6 per cent), myalgia or arthralgia (“muscle or joint ache” – 14.8 per cent), chills (11.4 per cent), nausea or vomiting (5.0 per cent), nasal congestion (4.8 per cent), diarrhoea (3.7 per cent), and haemoptysis (“coughing out blood – 0.9 per cent), and conjunctival congestion (0.8 per cent).

Mild respiratory symptoms and fever develop within 5-6 days after infection on average. Although the mean incubation period is 5-6 days, it ranges from 1-14 days.

About 80 per cent of the infected had mild to moderate disease which included non-pneumonia and pneumonia cases. 13.8 per cent had severe disease and 6.1 per cent were critically ill with respiratory failure, septic shock and/or multiple organ dysfunction/failure.

Asymptomatic infection had been reported but the majority of these persons went on to develop the disease. Truly asymptomatic infections appear to be relatively rare and does not appear to be a major driver of transmission.

The overall case fatality rate (“CFR”) was 3.8 per cent and it varied with location and intensity of transmission i.e. 5.8 per cent in Wuhan and 0.7 per cent in other areas in China.

The overall CFR was higher in the early stages of the outbreak (17.3 per cent for those with symptom onset from 1-10 January 2020) but reduced with time to 0.7 per cent for those with symptom onset after 1 February 2020. The standard of care had evolved during the course of the outbreak.

Those who are at highest risk for severe disease and death include those aged above 60 years and those with underlying conditions like high blood pressure, diabetes, cardiovascular disease, chronic respiratory disease and cancer.

Mortality increases with age with the highest among those aged 80 years or more whose CFR was 21.9 per cent. The CFR for males was 4.7 per cent and 2.8 per cent for females. The CFR of those who had no co-morbidities was 1.4 per cent compared to 13.2 per cent for those with cardiovascular disease, 9.2 per cent for diabetes, 8.4 per cent for hypertension, 8.0 per cent for chronic respiratory disease and 7.6 per cent for cancer.

Disease in children appeared to be relatively rare and mild with 2.4 per cent of the total cases in those under 19 years, of which 2.5 per cent developed severe disease and 0.2 per cent critical disease.

The median time from symptom onset to laboratory confirmation nationally decreased from 12 days (range 8-18 days) in early January 2020 to 3 days (range 1-7) in early February 2020. This facilitated earlier case and contact identification, isolation and treatment.

What is unknown

Although much is known about Covid-19, there is still much more that is unknown. They include:
• Source of infection — Animal origin and natural reservoir of the virus; Human-animal interface of the original event; Early cases whose exposure could not be identified.
• Pathogenesis and virulence evolution of the virus — Bats appear to be the reservoir of the virus, but the intermediate host(s) has not yet been identified.
• Transmission dynamics – Modes of Transmission (Role of aerosol transmission in non-health care settings and Role of faecal-oral transmission); viral shedding in various periods of the clinical course in different biological samples i.e. upper and lower respiratory tract, saliva, faeces, urine (Before symptom onset and among asymptomatic cases; During the symptomatic period; After the symptomatic period / during clinical recovery).
• Risk factors for infection – Behavioural and socio-economic risk factors for infection in households/ institutions and the community; Risk factors for asymptomatic infection; risk factors for nosocomial infection among health care workers and among patients.
• Surveillance and monitoring.
• Laboratory and diagnostics.
• Clinical management of severe and critically ill patients.
• Prevention and control measures.

Messages for the public

The WHO’s messages for the public are:
• “Recognise that Covid-19 is a new and concerning disease, but that outbreaks can managed with the right response and that the vast majority of infected people will recover;
• Begin now to adopt and rigorously practice the most important preventive measures for Covid-19 by frequent hand washing and always covering your mouth and nose when sneezing or coughing;
• Continually update yourself on Covid-19 and its signs and symptoms (i.e. fever and dry cough), because the strategies and response activities will constantly improve as new information on this disease is accumulating every day; and
• Be prepared to actively support a response to Covid-19 in a variety of ways, including the adoption of more stringent ‘social distancing’ practices and helping the high-risk elderly population.”

Dr Milton Lum is a past President of the Federation of Private Medical Practitioners Associations, Malaysia and the Malaysian Medical Association. This article is not intended to replace, dictate or define evaluation by a qualified doctor. The views expressed do not represent that of any organization the writer is associated with.

  • This is the personal opinion of the writer or publication and does not necessarily represent the views of CodeBlue.

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