An Infectious Diseases Specialist Perspective for Planning for the Next Pandemic
Key Points Addressed in Article
- A review of Epidemiology
- The Stages of an Outbreak
- Ways to Begin thinking about protecting yourself from infection
The Emergence of the novel Coronavirus
The caseload of those infected with COVID-19 continues to ascend in an exponential manner in China; with spread mainly with those traveling from the outbreak zone to multiple neighboring and more distant countries, including Germany, France, Italy, Iran, Canada and the United States.
What began in an animal marketplace in the bustling city of 11 million in Wuhan, China, has developed into 75,129 cases predominantly in Wuhan and other parts of Hubei province. Public transportation in 17 populous cities in China has been suspended, as the Chinese government grapples with trying to contain the illness.
The first case of COVID-19 was reported on December 31st, after a person developed symptoms three weeks earlier (December 8th), along with 27 other cases (suspected) over the course of a few weeks. COVID-19 has now approached pandemic proportions. All of this is happening during one of the busiest times in China, the Lunar New Year.
Infection Characteristics: A Review of Epidemiology
In order to understand the gravity of the novel coronavirus, it is important to define some epidemiology terms: attack rate and mortality rate. The attack rate represents the number of people who acquire an illness divided by the number of those at risk. The mortality rate is the number of those that have died from the infection divided by the amount of those infected.
Even when a disease has a lower mortality rate, if it has a high attack rate, it can make a severe impact. The seasonal flu has an estimated attack rate of 10-20%. This means about one-fifth of the US population may contract influenza during the season! During the current flu season, the CDC estimates that there have been up to 21 million flu illnesses in the United States, with up to 10 million flu medical visits, 250,000 flu hospitalizations and up to 20,000 deaths related to the flu.
With the amount of cases of seasonal influenza, the mortality rate is around 0.1% (9 cases/100,000). Thusfar, with the 75,129 cases reported of the COVID-19, there were 2,007 reported deaths (mostly in Wuhan) making the estimated mortality rate 2.6%. This is expected to change, as more cases are identified. If the attack rate of COVID-19 is similar to influenza, it will have a significant impact across the globe if it is not contained. Diseases with menacingly high mortality rates, such as SARS (10%), Avian flu (59%), and Ebola (50-90%), have lower attack rates, meaning they were not able to affect as many.
What’s particularly more concerning is the amount of severe cases reported, which, if the number is accurate, a rate of 21% of those infected with COVID-19 have a more severe infection. Though, most likely these cases are among the highest risk populations for severe disease, the very old and those with chronic diseases.
Another thing to keep in mind: When epidemiologists determine the above rates, they must ensure an accurate numerator and denominator. Oftentimes, the first cases that are identified are the more severe cases – making the estimated mortality rate higher than it may actually be. When you tally up the cases of milder diseases, your denominator increases, and the mortality rate consequently decreases.
An illness that can cause mortality and be spread easily requires preparation and containment strategies.
Was the rapidity of this process predictable?
The first case of COVID-19 was believed to have been acquired at a market in Wuhan – and was reported as a novel infection on December 28th. There were 27 other people that were being evaluated for viral pneumonia during that time. One day following, a report of a family cluster of six patients who flew from Shenzhen to Wuhan on December 29, 2019, started presenting with influenza like symptoms on January 1, 2020. None of the family members had contact with markets or animals in Wuhan. This suggests that they were exposed to secondary cases (i.e. person-to-person) by the time that the primary case was identified as having the novel coronavirus.
Given that this disease emerged during the flu season, it is not unusual that it took some time to differentiate this from the usual viral infections. The usual “shotgun” gene sequencing tests were used including respiratory viral panels. Samples were sent for further methods to identify it as a novel coronavirus, similar to those of bat origin.
There are several phases to an outbreak (pictured below). Phases 1 to 3 relate to animal infections with few human infections. Phase 4 is related to human-to-human transmission, when the virus possesses an Ro of greater than 1. The epidemic was already well into phase 4 sustained human transmission by the time it was identified. Given that respiratory viruses, such as influenza, respiratory syncytial virus (RSV) and coronaviruses are transmitted by respiratory droplets as little as 10 microns (micrometers), the diseases can be easily transmitted with casual contact, shaking hands, or touching contaminated surfaces or objects (fomites). Remember these droplets can get passed not only from the secretions from sneezing or coughing, but also saliva from talking. At phase 5 to 6, there is widespread human infection. The “post peak” period is when there is still the possibility of recurrent epidemic surges, as the virus may be still re-intruduced to an uninfected population. Finally, the post pandemic period is when enough of herd immunity from acquired infection (or vaccination) allows for the disease to be controlled.
Any respiratory disease has the capabilities of exponential spread over a short period.
What can one do to protect themselves from this scourge?
A simple surgical mask, when worn correctly (sealed well around the nose), is probably sufficient to prevent particles larger than 5 microns from entering the mask. Since respiratory droplets are larger than this size, risk of transmission is expected to be low. Although an N95 mask offers greater protection for very small particles (0.3 microns), it is likely unnecessary to prevent transmission of COVID-19. Nevertheless, until the dynamics of transmission are understood better, the CDC recommends healthcare workers to use N95 masks. As with SARS, an important risk group for acquiring the disease is healthcare workers.
The average amount of people infected per person is a little higher than influenza (estimated 1.5-4 vs. 1.5-2.5), suggesting there may be some airborne droplet spread. Though, in contradistinction with measles, which is associated with airborne droplet transmission and can be as high as 20 people, it is likely that COVID-19 is mostly transmitted by larger respiratory droplets.
Another important recommendation is that someone who suspects or is suspected of having the infection should comply with using a mask and washing hands after touching his/her face.
Do we need to stock up and “hunker down”?
Preparation for an apocalypse is a common theme in many popular movies and streaming series. While COVID-19 is expected to make a significant wave of disease throughout the world – which is what I gather when I see the case reports double in a day – it is unlikely that it is going to have a major impact on most of our lives. It is always sad to hear of people who develop complications or die from this infection – and one excess death from this infection is one too many. Rather than the infection, fear and panic is likely to have a greater impact on order and stability.
The containment measures seem to have made some progress on reducing new cases spread outside of Wuhan and Hubei province. Though, from what we learned with with the recent infections in South Korea, Italy and Iran, it can change in a day.
There is always a possibility that the virus may transform as it is spreads from human to human – potentially becoming more virulent. If that were to occur, the dynamics of the attack rate would likely change. I don’t expect that we will see this with COVID-19.
As for now, my recommendation would be to keep informed of the disease rates while reading the news or listening to the radio. These rates are constantly being updated throughout the day. Staying glued to this information is likely not beneficial and may be hazardous to your mental health – increasing fear and panic.
Seasonal influenza has made a greater impact and your likelihood of getting it is much greater too. So if you still haven’t been vaccinated, it is never too late.
I was recently featured on KGW regarding risk factors for Coronavirus, after a Portland women and her family were quarantines aboard a cruise ship for 2 weeks. She was essentially asymptomatic.
Categories: Infectious Diseases Topics