Dr Siddharth Sridhar 
Clinical Assistant Professor 
Department of Microbiology

The oft-used term ‘emerging infectious diseases’ usually brings up images of periodic cataclysmic contagions of pathogens like COVID-19 or bird flu. However, in reality, emerging infectious diseases are all around us, sight unseen. As a clinical virologist, I am acutely aware of this whenever I see patients being discharged without a microbiological diagnosis for syndromes like hepatitis, pneumonia, or fever. These hidden infections often cause mild illness or are poorly transmissible; they may occur far from urban centers, seldom triggering public health responses. Nevertheless, they are important – to patients and their doctors (for there is no treatment without a diagnosis), to societies, and to researchers trawling the Earth’s microbiome for the next big pandemic agent. 

I learned this in 2017 when I was fortunate enough to recognize and report the world’s first human case of infection by rat hepatitis E virus. By establishing a city-wide diagnostic network for rat hepatitis E, we managed to ‘crack the case’ for a number of patients with otherwise-unexplained hepatitis. Rat hepatitis E is the archetype of an emerging infectious disease hiding in plain sight. Most infections are mild and it is poorly transmissible. But rat hepatitis E has an outsize impact on the immunocompromised population: although only causing 10% of cases of hepatitis E overall, it accounted for half of all the chronic hepatitis E cases recorded in the city since 2017. Establishing this diagnosis was vital for these patients because rat hepatitis E is curable with ribavirin. 

The on-going epidemic of rat hepatitis E also served as a bellwether of public hygiene and rodent infestation in Hong Kong. Liaising with government and private organizations to set up a street rat hepatitis E surveillance project taught me more about the intricacies of pest control than I would ever have imagined possible.  But, perhaps most gratifying of all is seeing my colleagues overseas begin to find rat hepatitis E in their patients in Europe and North America. This, for me, is the best part of clinical research – the impact is immediate, transformative, and certain. This is why I stay in academia.  

While we remain vigilant for the next pandemic agents, let’s not forget the small guys. In my opinion, the widely touted ‘big data’ obsessed infrastructure drive is inadequate to discover these pathogens. My approach is the opposite: I love well-curated small data that is as close as possible to what doctors face in the wards every day. There are so many discoveries waiting to be made there.