• Andrew Lee

The Bigger Picture — an Interview with a Public Health Epidemiologist

An apple a day keeps the doctor away. To most of us, public health was never an unfamiliar topic. During these unprecedented times, public health has become the major concern worldwide and we are more than honoured to have invited Dr. Ryan Au Yeung to enlighten us with his research, his work done related to COVID-19, and his views and knowledge of the difference between public health and clinical medicine.

Dr. Au Yeung completed all of his studies in Hong Kong University, including Biology during his undergraduate studies, Public Health for his Masters and Epidemiology in his PhD study. After his graduation, he was presented with the opportunity for an academic exchange in Columbia University for a duration of 3 months. During the exchange, he got to work with professors related to public health, learning different approaches or methods to tackle problems effectively. Afterwards, he continued to work at HKU as an assistant professor at the Li Ka Shing Faculty of Medicine, School of Public Health.

His primary research includes exploring genetic determinants and various diseases, and his main focus is on cardiovascular diseases. Apart from research, he also teaches students in the Bachelor of Medicine, Bachelor of Surgery (MBBS) program and Global Health and Development (GHD) program, which touches upon globalization and its effects on the world, both economically and in terms of public health.


As Dr. Au Yeung says, public health and clinical medicine both have their advantages and functions in different ways. It’s hard to compare which is of more superiority as they tackle problems in different ways. In clinical medicine, a doctor treats a patient directly through consultation and prescription. However, in public health, the target is not an individual but in fact a group of people and similar health problems — the sample size ranges from a few thousand people to over tens of thousands of people. In terms of specialty, one has to be a physician in order to work in clinical medicine, but one doesn’t necessarily have to be a physician for public health. Public health specialists consist of an interdisciplinary team with different backgrounds including physicians, social scientists, economists, people with legal backgrounds etc. They communicate with different stakeholders, catering their needs in order to facilitate effective public health intervention and assist the government in policy making, notably the recent COVID-19 pandemic.

Clinical medicine doctors are generally more focused on disease specific phenotypes (e.g. heart disease or cancer), looking deep into physiological pathways or cell culture. As they deal with a smaller sample size, they can probe their patients from top to bottom using CT scans or MRI, investigating intricate structures. On the other hand, public health doctors focused more on the determinants related to future health risk, such as blood pressure, lipids and body mass index. Given they deal with a larger sample size, it is therefore infeasible to do thorough scans on every one of them due to the timeliness and large economic costs of such actions. However, this does not mean that clinical medicine doctors can provide more help to patients when compared to public health doctors. Dr. Au Yeung said, “Imagine a group of people falling down from a bridge and were drowning. The ones who immediately set out for rescue would be the clinical medicine doctors; the ones who investigate the infrastructure of the bridge and aim to better the design of the bridge would be the public health doctors." Both of them help the public in different ways and yet they have to work hand in hand in order for the public to have a better quality of life.

OKAY let’s do research but what method should we use?

As mentioned above, Dr. Au Yeung's research mainly focuses on genetic determinants, he therefore mainly uses Mendelian randomization on his research. Mendelian randomization represents a novel epidemiologic study design which incorporates genetic information into traditional epidemiologic methods. Having cutting-edge technology and experience in this aspect, Dr. Au Yeung is one of the pioneers in this research method. From gene-related studies to genome sequencing, genetic information related to health and disease expands adjacent to the ever-growing "big data force", which also partially led to the rise of studies based on Mendelian randomization nowadays. The method also provides an alternative pathway to address questions of causality without going through typical biases that might adversely affect the validity of traditional epidemiologic approaches.

Eliminating biases is one of the most prominent advantages of using randomized controlled trial (RCT). In RCT, the subjects are randomly assigned to one of the groups, that is the experimental group receiving the intervention to be tested, or the control group receiving the conventional treatment or a placebo. Confounding factors and chance of individual factors, potential errors due to bias can then be minimized. The groups’ outcome can then be compared so that the effect of the independent variable can be known directly. However, there are limitations of such a test. Dr. Au Yeung concluded that although RCT can provide a fairer test, it is unsuitable under some circumstances. For example, concerning the effect of winery, it is hard to have a control group of people not drinking wine for 10 years at all, and thus the feasibility is low.

In this case, observational studies would come up as the upper hand. For instance, using RCT to allocate a group of patients to drink alcohol in order to investigate the relationship of alcohol with cardiovascular diseases is clearly unethical. Simply recording the health conditions of a group of regular drinkers would show the effects in a straight-forward manner. “Observational studies appear to be a very useful tool in epidemiology,” says Dr. Au Yeung. The public concern stacked upon the practical or ethical issues for RCT is then non-existent for observational studies. However, unlike RCT, it is more prone to confounding and bias as there is no randomization in the study group. For instance, Dr. Au Yeung proposes this situation: Say we are to investigate if consuming more vitamin tablets promotes health, however, people who consume more vitamin than the average person are more likely to have a wealthy background or higher quality of life. The physical conditions and psychological impacts would then tend to be better and less respectively when compared to the average being.

How should I find research inspiration?

Dr. Au Yeung suggests to start reading as the first step. Searching for suitable resources would then be next. He also shared how he overcame his challenges step by step during his research. “When I was studying Mendelian randomization for my PhD, the method was pretty new to society, it is not as straight-forward as other well-established methods. People were not entirely clear about Mendelian randomization, including me and my mentor at the time. Discovering it step by step, finding possible ways, it seems as if I were developing side by side with the method.

“Through these challenges, one would then know how to overcome similar challenges in the future. “I take these challenges as beneficial opportunities,” laughed Dr. Au Yeung.

So how exactly are public health investigations incorporated in COVID-19 policies?

Dr. Au Yeung and his team pay close attention to the number of people who were previously exposed to SARS-CoV-2 virus using a serosurvey design, whilst other public health researchers look at the trend of number of infectants, looking for possible upward trends, downward trends, or even a sudden outbreak due to a surge of the numbers. Some also created a mathematical model along the way in order to aid their investigation, such as investigating the amount of subsequent cases that one case of COVID could lead it. Based on various types of evidence, the public health researchers could easily figure out the reproductive number of COVID-19, i.e. the average number of people infected by one patient. They then pass on this evidence to the government for policy making.

Qualities suitable to be a public health doctor

“Public health is of an interdisciplinary nature,” comments Dr. Au Yeung. Communication skills are therefore deemed as one of the most important attributes as communicating with physicians, social scientists, economists, lawyers etc. appears as a norm. Moreover, due to government policies which aim for the betterment of public health leading to side effects — such as a drop in economy — public health doctors should have bright minds. Take the recent lockdown in Yau Ma Tei as an example — citizens were forbidden to leave the area, fulfilling the policy of isolation. However, economic activities might then be hindered in the area. Public health doctors, especially those working at a senior level in health authorities (e.g. Food and Health Bureau of HKSAR Government), hence have to consider multiple perspectives at a time, catering to the needs of several stakeholders.

To be or not to be… that is the question. To be a public health doctor, interest should always be of utmost importance for consideration. Along the ever-extending pathway of medical pursuit, the ends are limitless. You do not have to be constrained by a single aspect in the sea of medical career pathways. To shine bright, find your interest for medicine, find your love for medicine, and most importantly, find your passion for medicine.

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