Knowing who and how many people currently have the virus versus those who’ve already had the virus but have now recovered from it might provide important information that will guide our communities, public health systems and governments as we move forward through this pandemic.
How does COVID-19 spread?
As we now know all too well, human-to-human transmission of SARS-CoV-2 is not only possible but moreover occurs at a very high rate. Like the seasonal flu (but with a higher transmissibility), SARS-CoV-2 is spread mainly by respiratory droplets. Touching infected surfaces then touching your own mucous membranes (for example, your nose and mouth) can also lead to infection. Aerosolizing procedures would also promote spread.
The diagnostic test is most commonly a swab of your nose/throat which can detect the presence of virus RNA (SARS-CoV-2 is a single-stranded RNA virus) and indicates if you currently have the virus. Think of it as a snapshot in time, of whether you have the virus right now. In the event that you do have the virus but do not have any symptoms, you would still be able to infect others.1 If you did have the virus and no longer have it, the scientific community is rapidly developing the ability of knowing this too (this would be a blood test and is known as serology).2 It is controversial whether those who have already been infected by SARS-CoV-2 would have a certain immunity moving forward.2
Knowing who and how many people currently have the virus versus those who have already had the virus but have now recovered from it might provide important information that can guide our communities, public health systems and governments as we move forward through this pandemic.
What are the symptoms of COVID-19? Are there risk factors for disease severity?
Across the many populations around the world that have been studied, those who do get sick from the virus tend to have similar types of symptoms. Reports from epicentres Wuhan, China and New York, USA both reveal that patients with COVID-19 most often present with shortness of breath, a dry cough, fever and fatigue.3,4 Other symptoms are also possible including gastrointestinal symptoms (diarrhea, nausea and vomiting)4 and even loss of smell.5 Though it may not necessarily affect if you catch the virus, important risk factors for developing severe disease include older age and co-morbid disease.
Common co-morbid diseases that increase risk of severe disease include high blood pressure and diabetes. Patients with heart and lung conditions, cancer and conditions causing low immune systems are at higher risk of needing a ventilator and of death. Amongst lung conditions, patients with COPD may risk having more severe disease courses and complications if they do catch the infection.6-8 In future blogs we will discuss specific sub-topics as they relate to chronic lung disease care during the pandemic. The bottom line for our readers with chronic lung disease: prevention is key!
What do we know about the mortality rates of COVID-19?
Accurate survival rates are difficult to obtain for several reasons. It depends on the population being studied (including differences in risk factors, co-morbid conditions and healthcare system capacities). A mortality rate needs a numerator (those who have died from COVID-19) and, importantly, a denominator (all members of the population infected with the virus) – another reason why the ability to test and diagnose is so important.9
It also depends on when the numerator and denominator are spaced in time from one another (a common strategy is to use the global numerator around 2 weeks prior to the global denominator – a reflection of the incubation time of the virus). Global mortality rates hover around or below 5%, however depending on the population studied and their choice of numerator/denominator, other estimates have been higher than this.9 Our understanding of these statistics, and of the virus itself, continues to grow as the global scientific community continues to collaborate and study this disease.
About the author
Bryan completed his medical school and Internal Medicine residency at the University of Toronto, and his Respirology fellowship at the University of Alberta. Prior to this he completed his undergraduate degree at Queen’s University and his master’s degree in Physiology at McGill University. He has had a longstanding clinical and research interest in respiratory and cardiac physiology and applied exercise science, in pulmonary rehabilitation, and in the management of chronic respiratory disease. He is currently completing an additional fellowship at the Montreal Chest Institute (McGill University Health Centre) in pulmonary rehabilitation and chronic disease management.