Understanding COVID-19 in Northern Ireland through the lens of surveillance and epidemiology

Dr Lynsey Patterson, Head of Health Protection Surveillance, PHA, and Dr Claire Neill, Specialty Registrar in Public Health, PHA

COVID statistics graphic

Since December 2019, the world has been getting to grips with the COVID-19 pandemic. As the outbreak spread, so did the need to have timely and accurate information on the number of cases, where they occurred, and a measure of how bad the disease is by understanding how many people have unfortunately lost their lives to COVID-19. Disease surveillance, or the activity behind the numbers, has been thrust into the limelight as has the need for ‘information for action’ across the globe.

Surveillance is designed to add a level of context to support analysis and interpretation of the raw data. The key aspects of any surveillance programme are: a clear definition (the case definition, which allows us to understand what we are measuring and compare with similar programmes elsewhere); that it provides sustained observation over time (compared to a one-off survey or research projects); and that it is timely (which can come at a cost in terms of provisional and less validated information). Collectively, these elements ensure that a surveillance system can provide data which, when analysed and interpreted, can be used to plan our immediate response to the disease.

In order to report on all aspects of COVID-19, we have been working in earnest since February 2020 to develop new surveillance systems. These systems have enabled us to understand who has been affected by the disease, or the epidemiology of cases, which is particularly important for a new disease, like COVID-19, that we knew very little about six months ago. We have introduced systems to detect disease increases at an early stage in the community (primary care surveillance) and in vulnerable groups (care home and critical care surveillance), all requiring unique approaches to collecting data. Having these systems in place is critical for the early detection of any increase in COVID-19. We also have systems in place for monitoring the numbers that have passed away as a result of COVID-19 (mortality surveillance), which we previously described in our blog series.

In May 2020, we published our first epidemiological bulletin which brings together information from all of these different surveillance systems to tell the story of COVID-19 infection in Northern Ireland. The bulletin complements other sources of information on COVID-19 such as the daily monitoring made possible by the Department of Health’s COVID-19 dashboard, to which we also contribute.  

In this second report, we have added new information on testing. This reflects the additional testing capacity available as part of our National Testing programme. Collectively, this shows that the number of cases in Northern Ireland continues to decrease despite high levels of testing. It is useful to consider the proportion of positive test results (also known as a positivity rate) which shows that while the level of testing has increased, the proportion that are positive has declined and is currently around 5%.

The majority of people diagnosed with COVID-19 infection in Northern Ireland have, to date, been female (60%), although the death rate is highest in males. The vast majority of hospital admissions have been in those over 80 years of age. The highest incidence of disease continues to be in Belfast, which may reflect the higher density of people in this area. The number of new cases of COVID-19 in our most vulnerable groups, those in critical care and the elderly in care homes, including care homes experiencing an outbreak of COVID-19, continues to fall (Figure 1). This reflects the concerted effort, particularly in care homes, to quickly respond and manage new cases in these settings. When we look at our community surveillance, we see large reductions in the numbers of people presenting to primary care with new respiratory symptoms which corresponds with the introduction of stay at home advice in March 2020.

Figure 1: Percentage of care homes in Northern Ireland with a suspected or confirmed outbreak of COVID-19

The surveillance team also coordinate Northern Ireland’s participation in European and Global Programmes. One such programme is the European Mortality Monitoring Project (EuroMOMO) which is designed to detect and measure excess deaths related to public health threats, such as influenza. Monitoring excess deaths, those above which we would expect to see in ‘normal’ conditions, is important as it allows us to quantify the impact of a situation like COVID-19 when not all causes of death are known. This has shown, similar to other parts of the UK and Europe, that we have seen some rise in deaths during April 2020. This is returning to normal, but may rise again in the future.

We have all had to adapt rapidly to a world with COVID-19 and our surveillance response has been no different. Despite sustained pressure earlier this year, we are in a position to detect and respond to any changes in the disease or pandemic, as these emerge, perhaps over the coming winter.   Data analysis can seem far away from the experience of individuals and we need to bear in mind the human cost associated with each death or hospital admission.

We hope this helps you understand the core elements of a surveillance system, why it is important, and how it can be used to protect the health of our population. Keep an eye out for future blogs, aiming to explore in more detail specific actions we are taking in response to the COVID-19 surveillance data. To see the epidemiological bulletin, which will be released at least monthly, please visit the Public Health Agency website.

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