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A Great Explanation of COVID 19 By Dr Des Crowley

Dr Des Crowley has provided us with a guest blog post on an explanation of COVID 19 and how it works.

I find epidemiology and infectious diseases fascinating. They combine science, mathematics and sociology in equal parts. COVID 19 is a fast-changing pandemic that is now challenging health services globally.

On the advice of the world’s best public health experts, governments are implementing unprecedented measures, including mass shut downs of schools, businesses and borders. I have put together a few pointers that might give people a better understanding of this life-changing epidemic.

COVID 19 is a disease caused by a virus. It was first identified in China at the end of 2019. By the end of January 2020, the first cases of COVID 19 were identified in Italy, Spain and the UK. Ireland had its first confirmed case at the end of February. The first cases identified in European countries were from people traveling from areas where infections were already identified and these were all followed by community transmission.

The greatest difficulty with COVID 19 infection is that it can be transmitted by people who are asymptomatic. This is unlike SARS which was caused by a similar type virus but was only transmitted by symptomatic patients. This allowed this emerging epidemic to be curtailed so that it did not develop into the pandemic we are now experiencing.

Because it can be transmitted by asymptomatic patients the only way to effectively reduce transmission is to practice personal and environmental hygiene and social distancing. Washing hands, adhering to cough and sneeze etiquette and staying 2 metres apart prevents us coming in contact with the virus. Cleaning potentially contaminated surfaces prevents us getting our hands contaminated and infecting ourselves by wiping our faces (particularly eyes and mouths).

We hear a lot about ‘flattening of the curve’. The reporting and monitoring of epidemics are all about infectivity rates and percentage increases in new cases. Some people find percentages difficult to understand. It can help to interpret them by imagining a crowd e.g. 1000 people (the capacity of the Olympia theatre) (1% of this crowd is 10) or larger groups (Croke Park has a capacity of 80,000) (10% of this population is 8,000 people). While absolute numbers are important, they don’t tell us much about the progress of an epidemic. The best indicator is the rates of increase of new infections (how fast the infection is spreading). Flattening a curve in an epidemic allows health services to adapt to the challenges and it also allows us time to look for better ways to manage the disease, find cures and develop vaccines. However, the flattening of the curve may not impact on the overall numbers of infections or deaths (the same number will occur but over a longer period of time).

The rates of infection and deaths in Italy and Spain have upset us all. Watching these harrowing images feels apocalyptic and it is difficult to imagine how these might translate to Ireland. Clearly both Spain and Italy are larger countries (populations of 46 million and 60 million respectively). Dividing the numbers by 10 and 12 will allow you to compare with Irish data (Republic of Ireland has a population of 5 million). When comparing with Irish figures its important to understand that we are a month behind both countries on the curve and we differ culturally and in population profile from both countries.

We have daily updates of new diagnosis and deaths from our public health experts. While helpful they need to be interpreted with caution. There are significant delays in testing and diagnosis (2-10 days) and we are only testing very symptomatic people. The rates of new infections underestimate the real levels of community infection and are reflective of behaviours (level of social distancing and self-isolation) that are 10-14 days old. Despite these limitations the level of new infections in Ireland is encouraging and does give hope that the curve is flattening.

Presently COVID 19 testing is by a lab-based PCR test. This involves identifying the presence of the virus in nasal and pharyngeal swabs. The virus is usually present for 14 days so a negative test after this period is meaningless. We have heard much about an anti-body test being a game changer in how we manage this pandemic. An antibody test identifies blood markers produced in the body in response to the infection. These will persist once the infection is cleared and can determine that a person is now immune to the virus. This will allow people to return to front line work and feel safer. It is generally accepted in the medical world that once infected you will have ongoing immunity to re-infection. We are approximately 10 days to 2 weeks away from having a reliable anti-body test so do not be fooled into ordering these tests on line, they are inaccurate and you should not assume immunity based on their result.

There is a real possibility that we will have a point-of-care antibody test in the very near future. These will allow people to test from home and to have an accurate understanding of their immunity. This may well change how we manage the epidemic and may mean we move towards ‘herd immunity’ and protecting those considered vulnerable.

It is recognised that some people are more vulnerable to COVID infection than others, in particular older people and those with underlying illnesses and compromised immunities. However globally the biggest impact this pandemic will have is on the poor. The vast majority of people living in developing countries cannot socially isolate or practice social distancing. They do not have access to water to clean their hands and existing disease and malnutrition will make them even more susceptible. Rates of HIV infection is Africa will further exacerbate its containment.
The Irish health service has responded in a dynamic and effective way to this challenge. We have implemented new and efficient ways to provide healthcare and have introduced sweeping changes to how we care for our homeless and marginalised people. It is my hope that we can take these positive changes and learnings into the a post-COVID future and address some of the social and health inequalities experienced by some many.

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