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An evolving novel coronavirus epidemic

The novel Wuhan coronavirus outbreak has been changing on an almost hourly basis. It has been difficult even for infectious disease experts to keep up with a litany of new facts that are emerging regarding case counts, fatalities, and countries with importations. 

Yesterday, the World Health Organization (WHO) declined to declare a public health emergency of international concern (PHEIC). Since I first wrote about this outbreak, two cases have been diagnosed in the U.S. It has become clear that amidst this uncertainty, there several vital aspects that merit deeper consideration. 

Understanding the severity of illness

One of the critical elements of gauging the risk of an emerging infectious disease outbreak is understanding the ratio of mild to severe cases. In the early days of any epidemic, the reporting will be skewed to severe cases and will render any fatality estimates unreliable. 

It has been well established, even with the causative coronaviruses behind MERS and SARS, that there is a spectrum of illness. Some that are infected may have mild to no symptoms, while others have fulminant manifestations. 

As this outbreak unfolds, it is certain the number of deaths — currently numbering 26 will increase — but it is equally important to understand how many mild cases are occurring. It is essential to understand where this coronavirus is situated. Initial investigation of the first 42 patients revealed some to be quite ill, with 10 percent requiring mechanical ventilation.

Is it more like SARS or MERS or more like community-acquired coronaviruses? Are severe cases restricted or highly concentrated in those with underlying medical conditions? Germane to this question is the fact that WHO scoring for severity is incongruent with validated pneumonia severity scoring used by clinicians as the mere presence of dyspnea qualifies a patient for the “severe” label.

As mild cases are uncovered, it is crucial that they only are hospitalized when they require medical intervention lest they absorb scare bed space and place healthcare workers and other patients at risk for inadvertent infection. 

Transmissibility uncertainty

Probably the most significant factor behind the WHO’s decision to not declare a PHEIC are the questions surrounding transmissibility. While it is clear that human-to-human transmission has occurred — not all cases are related to an animal market — it remains uncertain if human to human transmission is commonly sustained. 

Are people who are infected with the virus through another person able to transmit to another person? There are reports of multiple generations of transmission. However, it appears, thus far, that human to human transmission has been restricted to family clusters and healthcare settings — something is seen with SARS and MERS. Reassuringly, most of the cases outside of China have seen secondary transmission (Vietnam has had one father to son transmission). If human to human transmission is not sustainable for this virus, it will facilitate containment. 

Travel restrictions

Currently, the Centers for Disease Control and Prevention (CDC) has issued a level 3 alert for travel to Wuhan, their highest designation, advising against the non-essential travel. Travelers to the U.S. from Wuhan are being funneled to one of five airports where they are not only being screened for illness but being instructed on what to do in the event symptoms develop post-screening (as was the case with the patient in the state of Washington). 

Meanwhile, in Wuhan and linked cities, the Chinese government has instituted an armed lockdown in which approximately 20 million residents are not permitted to leave the area. Such an action has a significant downside as residents behind the barricades will, understandably and quite rightly, feel trapped, stigmatized, and abandoned. Such a policy may paradoxically drive disease spread as people seek to escape or hide illness. Additionally, it may become more challenging to get resources into the epidemic epicenter. 

As the epidemic unfolds, we can be sure that we will see more cases diagnosed — including in the U.S. — and more deaths. However, it is crucial that our response is proactive yet measured and appropriately matched to the adversary we face.

Amesh Adalja, M.D., is an infectious disease physician and a senior scholar at the Johns Hopkins Center for Health Security. Follow him on Twitter: @AmeshAA.

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