China has a new SARS-like virus — how serious is it?

China has a new SARS-like virus — how serious is it?
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The last several days of infectious disease headlines have been focused on a mysterious outbreak in Wuhan, China, that has many concerning harbingers. This cluster of pneumonia cases —  some of which are severe — involves individuals who had exposure to a, since decontaminated, seafood market that housed many types of animals.

The initial evaluation of these patients, who became ill between Dec. 12 and Dec. 29, 2019, was unable to reveal any of the likely pathogens. Therefore these patients were determined to have unknown viral pneumonia, which has since been determined to be caused by a novel coronavirus.

These cases, which number 59 with seven labeled “critical," have led to justified precautions in many countries who are on alert for the importation of evidence and surging demand for masks by the Hong Kong public.


The Centers for Disease Control and Prevention (CDC) has issued a health alert to clinicians to inquire about travel to Wuhan as well as a level 1 travel alert for China (which suggests travelers take usual precautions).

Comparisons to SARS

Even before the identification of a novel coronavirus as the culprit virus, this outbreak had been linked by journalists and infectious disease experts with the 2003 eruption of Severe Acute Respiratory Syndrome (SARS), a disease process caused by a novel coronavirus with animal origins that also occurred in China.

In that incident, over 8000 cases and almost 800 deaths occurred as the virus swept the globe and created international disruption. Another novel coronavirus that shares a preference for severe disease with SARS, Middle East Respiratory Syndrome (MERS), has also been invoked

It is important to note that this new infection is, thus far, unlike SARS (and MERS) in at least two significant respects. First, there are currently no fatalities. SARS had about a 10  percent fatality rate, while MERS fatality rates reach around 35 percent.


There has been no apparent person-to-person transmission reported, and health-care workers are free of infection. This last suggests that this infection may not be highly contagious between humans, as health-care workers would be at high risk and could serve as sentinel indicators for contagiousness. However, the fact that 59 cases have occurred seems somewhat high for an exclusive animal-to-human transmission route.

Coronaviruses are a significant cause of the common cold but have pandemic potential

Post-SARS, it has been common to associate coronaviruses almost exclusively with severe disease. However, it is crucial to remember that these viruses, which resemble a crown when viewed with an electron microscope, are much more likely to cause uncomplicated upper respiratory infections, i.e., the common cold.

Before SARS, the first human coronaviruses described were thought of as one of the many common cold viruses without much concern for any more severe infections in those with a healthy functioning immune system. SARS drastically changed that misperception and has since placed coronaviruses, for good reasons, near the top of pandemic threats. 

Those reasons include the fact that coronaviruses are spread via the respiratory route, have shown their ability to cause severe disease, have many strains circulating in animal reservoirs such as bats, and have no effective vaccine or antiviral available.

This reconceptualization of the risk of coronaviruses has since led to the discovery of novel coronaviruses. In addition to MERS, two other human coronaviruses have been discovered (NL63, HKU1).

Both of these discoveries, unlike the events in Wuhan, did not initially involve clusters of infection such as in Wuhan but were the result of aggressive diagnostic testing in individual patients. However, these coronaviruses, though "novel," are not necessarily rare, as studies have shown that HKU1, for example, accounts for many cases of coronavirus infections. 

Key questions: Spectrum of illness, animal reservoir, family tree

The concern regarding this outbreak will remain justified until a critical issue is answered. What is the severity of the disease? Most respiratory infections have a spectrum of illnesses where some have minor symptoms, while others can have more severe complications such as pneumonia or respiratory failure. Understanding what the usual course of infection will be is crucial.

Is this novel coronavirus syndrome more akin to the common coronavirus infection, or is it more like MERS and SARS? Do those that have been deemed critically ill have other medical conditions such as diabetes, emphysema, or cardiovascular disease that explain the severity of illness? How is critical illness being defined? Which animal in the live market is the likely origin for the virus, and how is it acquired? Do all case-patients have contact with the suspected animal? Where does this novel coronavirus genetically fit in the human coronavirus group? There are 15 positive samples, were the others negative, not tested, or caused by something else?

As this outbreak unfolds, total transparency and real-time information dissemination should be expected. Thus far, most of what is being reported are reassuring and a testament to improvements in health security that have occurred in China post-SARS. The occurrence of this outbreak, irrespective of its outcome, should serve as a reminder to the world about the priority that must be placed on adept and prompt management of infectious disease emergencies at their earliest stages. 

Dr. Amesh Adalja is a senior scholar at the Johns Hopkins Center for Health Security. He is also a board-certified in infectious disease, critical care, emergency medicine, and internal medicine. Follow him on Twitter @AmeshAA.