COVID-19: Numbers that matter

Call it by any other name, it is still the same. But the World Health Organization announced yesterday the “official” name for the novel Coronavirus that has hogged the recent health headlines. According to WHO Secretary-General Dr. Tedros Adhanom Ghebreyesus, “the name should not refer to a geographical location, an animal, an individual or group of people, and is pronounceable and related to the disease. Having a name matters to prevent the use of other names that can be accurate or stigmatizing. It also gives the WHO a standard format to use for any future coronavirus outbreaks.

Do numbers matter?

The problem with numbers is how they are interpreted. Or misinterpreted. And the numbers become troubling, as they leave more questions than answers to an already confused public.

As of this writing, there are 45,153 cases and 1,115 deaths. The case fatality rate (CFR) now stands at 2.47%. But that is just an estimate as CFR is the number of known deaths divided by the number of confirmed cases. This does not represent the true CFR as we don’t know the actual number of cases there are (patients who are asymptomatic may be positive and yet not get tested). There are several ways epidemiologists look at the numbers we know. The table below shows the current information regarding COVID-19. Making heads or tails and interpreting the graph can be done positively or negatively.

The American Journal of Epidemiology [Ghani AC. Donnelly CA, et al. “Methods for Estimating the Case Fatality Ratio for a Novel, Emerging Infectious Disease”, Am J Epidemiol 2005;162:479-486] cites a method that could reasonably work well if the hazards of death and recovery at any time t measured from admission to the hospital, conditional on an event occurring at time t, are proportional, would be to use the formula:

CFR = death/(deaths + recovered)

Using this formula and the data above, the worldwide CFR would be (1,115/[1115+4894]) = 19%. Let’s remove all the cases in mainland China (which are a lot). The total number of deaths outside of China is 2, while the number of recovered is 54. Using the same formula, we now get 2/(2+54) = 3.6% CFR for patients outside of China. The National Health Commission (NHC) of China on the other hand utilizes the simplified formula:

Cumulative current total death/current confirmed cases

Using this formula, we now get 1,113/44,436 = 2.5% (this is based on 44,636 cases confirmed in China, with 1,113 deaths or 99.8% of the mortality is in China). Outside of China, only 2 patients have died as of this writing. There are 517 cases (1.14% of all the cases in the world) outside of China.

How contagious is the COVID19?

Attack rate or transmissibility of a virus is indicated by the symbol Ro (reproductive number, pronounced as R-nought or r-zero). It represents the average number of people to which a single infected person will transmit the virus.

Let’s look at a school as an example. Ro describes how many kids will get sick when one sick kid goes to class (population), based on the assumption that all kids are able to get sick (susceptibility). The disease itself and the interaction with these kids are important factors.

If Ro > 1, then more kids are infected. It doesn’t mean that the higher the Ro is the more dangerous the disease is. Some viral URIs (upper respiratory tract infections) can have a high Ro, while some deadly diseases a low Ro (< 1). If the Ro <1, then not everyone that comes in contact with the sick patient will get infected. If, however, the Ro >1, then the propensity to infect more kids is higher. Let’s say that the Ro ~ 15 (as in measles). This means that for every child diagnosed to have measles, he/she most likely will infect 15 more children. The other sick children would eventually infect other kids and in a short period, all the kids in one community would come down with measles in the shortest duration.

Unfortunately, COVID-19 is a relatively new viral pathogen. Because there is no vaccine or previous exposure by most patients, we are all susceptible to getting the disease (unlike vaccine-preventable diseases). In short, when people have immunity against a disease, people won’t get sick. But that’s not what we are seeing with COVID-19. This gets complicated with ‘super-spreaders’. If we use the school setting again as an example, the ‘super-spreader’ will most probably be the adults in school – teacher, principal, work staff, etc – who work with every child.

The computed Ro for COVID-19 is estimated at 2-3. Meaning for every (+) patient, he/she can potentially infect 2 to 3 people. Pertussis has the highest Ro value at 17-18, measles at 12-15, tuberculosis at 10, smallpox 4-6, Ebola anywhere from 1.34-2, and influenza (common flu) at < 2.

It is important to remember that Ro depends on several factors: contact, how long illness lasts (incubation period), how many contacts the person has encountered even before the symptoms have appeared (which makes asymptomatic cases troublesome because they don’t know they’re sick but they’re transmitting infection), and how often the illness spreads during each contact.

Are we over reacting?

For the moment, perhaps we should be more circumspect because of the lack of information in the diagnosis, treatment and true outcome of this disease. Consider the fact that as of this writing, there have been 1,115 deaths due to the COVID-19. This, however, pales in comparison to the fact that 56,600 people have died from seasonal flu ALONE this year!

Numbers that count should focus on what we know and what we can treat and prevent. For 2020 alone, HIV/AIDS deaths are now at 195,988, malaria at 114,358, smoking related at 582,822, alcohol related deaths at 291,596, and deaths from cancer at 957,528 (based on data as of this writing).

With the total number of communicable disease deaths at 1,513,600 (at 1 death almost per second) to date, note how death due to COVID-19 is at a measly 0.07% of deaths. That means that 99.93% of deaths from communicable diseases are unrelated to COVID-19.

Let’s focus on the ball while making sure we have adequate defense. Remember, panic will always be a bestseller. Let’s not get derailed in our daily lives with data and information that you don’t understand but share. If we get swayed by media and other people who have turned the numbers for personal distraction, we may end up losing the war in communicable diseases.

The author was former professor in biostatistics and research methodologies at the University of Santo Tomas, Faculty of Medicine and UST Graduate School. His undergraduate and graduate studies are in Mathematics.

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