Anyone who has had internet TV, internet or print media will be likely aware of the novel coronavirus (nCoV19) #NameItAlready. Whilst you may be forgiven for believing this is the one that gets us, in all likelihood it won’t live up to the hype and fizzle out like it’s predecessor SARS. While nCoV19 is a public health threat, the public are perceiving it to be a larger threat than it is. If we have learned anything from SARS, this large gulf between expectation and reality could undermine control efforts against future contagions. A more nuanced examination of the threat posed by nCoV19 is required.
Coronaviruses are enveloped single stranded positive sense RNA viruses which cause diseases of birds and mammals. Enveloped viruses are prone to desiccation, limiting their survival in the environment to hours or days. Corona viruses have a 26 kilobase genome, which can be used to classify the organisms into several distinct lineages. In this instance, nCoV19 is closely related to SARS (80% genomic similarity). Genomic analysis of the virus has led to confusion over the likely animal reservoir of nCoV19, current literature suggests that the closest relative to nCOV19 is a bat coronavirus, whilst previous codon optimisation studies suggested an unlikely reptilian origin.
Importance to Human Health
Coronaviruses cause mild diseases, (now with 3 notable exceptions) as one of many aetiological agents which cause the common cold.
Little is currently known about the true number of individuals infected with nCoV19 the outbreak is still in its early days and epidemiologists are playing catch-up. Mortality rate figures currently circulating (3%) initially came from a study of 41 individuals hospitalised with the virus. This same figure has been used to claim that nCoV19 has a higher mortality rate than influenza. However, comparing apples with apples, some models suggest that only 5% of nCoV19 infections have been detected as most are mild and infected individuals do not require care. Therefore detected cases are more likely to be “serious”, which we presume means required hospitalisation, which is our current denominator in mortality rate calculations (3%). Comparing apples with apples, seasonal influenza has a five-fold higher mortality rate in serious cases (10-15%) making it much more lethal than nCoV19.
Human to human transmission has been observed with nCoV19. It is believed that the R0 is between 1.5 – 3.5 with several different numbers floating around in the literature. It must be remembered that this is an average number of secondary cases associated with each case. In some instances cases have infected up to 14 individuals (superspreaders), which is counter-intuitively reassuring as it hints at the potential to prevent excess spread of nCoV19 through targeted control measures, and should not generate alarm.
It all boils down to the case definition, most confirmed cases are hospitalised individuals. Given the clinical spectrum of coronavirus diseases, it’s not unreasonable to expect sub-clinical or asymptomatic cases exist in the community and are therefore not currently captured in the denominator used to calculate mortality rates. As these cases are detected through molecular studies the number of cases is going to grow. As we backfill the missed cases the virus will appear to be very transmissible, and a more realistic mortality rate will be observed.
Suspected case requiring diagnostic testing (not to be reported at European level)
Patients with acute respiratory infection (sudden onset of at least one of the following: cough, sore throat, shortness of breath) requiring hospitalisation or notECDC Surveillance Guidelines
In the 14 days prior to onset of symptoms, met at least one of the following epidemiological criteria:
• Were in close contact with a confirmed or probable case of 2019-nCoV infection; OR
• Had a history of travel to areas with presumed ongoing community transmission of 2019-nCoV; OR
• Worked in or attended a health care facility where patients with 2019-nCoV infections were being treated.
A person with laboratory confirmation of 2019-nCoV infection, irrespective of clinical signs and symptoms
The Real Risk of nCoV19
A transmissible virus which is lethal in the right host context (host genetics, comorbid patients, the elderly, vulnerable groups) will cause excess mortality in exposed populations. Historically, we have seen low or no mortality associated with these coronaviruses (MERS and SARS) in developed nations, which will likely be the case here. However, in environments with high population densities, added pressures on respiratory health (high rates of smoking, air pollution etc), and limited health resources, nCoV19 may cause excess mortality in its own right, and through creating system-block (healthcare allocated to treating nCoV19 patients prevents others receiving the treatment they need). Further, ACE2 in type II alveolar cells may be the biological basis of the higher mortality burden observed in Asian men. This virus is therefore of limited concern in the Australian context.
The real risk to the Australian community from this outbreak can be found in the children’s story The Boy Who Cried Wolf. The apparent gulf between current information and reality will make the public sceptical about the real threat posed by future contagions. We as experts need to accurately communicate the risks of nCoV19 to maintain legitimacy as information channels in future outbreaks. This however does not mean we should be apathetic of potential risks, which can be mitigated through hygiene measures for respiratory illness. As ever the public health message should centre on avoiding transmission any respiratory illness (especially influenza) to vulnerable members of our community.
- Zhao Y et al. Single-cell RNA expression profiling of ACE2, the putative receptor of Wuhan 2019-nCov Feb 2020
- Ceraolo C, Giorgi FM. Genomic variance of the 2019-nCoV coronavirus Feb 2020
- Read JM et al. Novel coronavirus 2019-nCoV: early estimation of epidemiological parameters and epidemic predictions. Jan 2020
- CDC. Disease Burden of Influenza. 2020
- AIHW. Influenza in Australia. 2020
- McGinnis R. PRO/AH/EDR> Novel coronavirus (19): China (HU) transmission dynamics