Dr. Stephen Thomas (State University of New York): capturing subjective patient experience of dengue

In a recent paper published in PLOS NTDs*, a group of researchers is capturing a more thorough and realistic overview of the true burden of dengue based on the subjective experiences of the patients infected with the dengue virus. Spanning a wide spectrum of infection, from the vast majority of asymptomatic cases to the fewer cases of severe dengue, the authors are developing a Dengue Illness Card to record patient experiences in view of developing a quantitative Dengue Illness Index to provide robust data on the true cost and burden of dengue in endemic regions, and to ultimately improve the tools available to evaluate the benefit of measures to counter dengue including drugs and vaccines. In this Infectious Thoughts interview, we speak to Dr. Stephen Thomas from the Division of Infectious Diseases at the State University of New York, whose career spans work as a medical doctor, a world-renowed researcher in infectious diseases and dengue in particular, and chief operating officer of all the US Army's medical labs, about the innovative thinking underpinning the Dengue Illness Index and its role in accelerating the understanding and control of dengue infection.

* Dengue illness index—A tool to characterize the subjective dengue illness experience

Stephen J. Thomas, Liane Agulto, Kim Hendrickx, Martin Erpicum, Kay M. Tomashek, M. Cristina Cassetti, Catherine Laughlin, Alexander Precioso, Alexander C. Schmidt, Federico Narvaez, João Bosco Siqueira, Hasitha Tissera, Robert Edelman

Published: October 4, 2018


The Dengue Illness Index (DII) was recently developed to improve the assessment of vaccine and drug efficacy by including variables related to the subjective disease experience of an individual having contracted the dengue virus. What gaps in the understanding of the disease is this index trying to bridge and what applications could this have in improving disease management?

There have been several guidelines for the diagnosis and treatment of dengue - the World Health Organisation has been at the centre of these efforts but there have also been other groups. One of the main issues has been to improve the classification or characterisation of the severity of dengue cases, and to use that information to try to prognosticate patients early on in their illness course to understand who is at risk for developing severe dengue and its potential complications. This then helps to decide who can be managed as in- an out-patients. The index which we have just published in PLOS NTDs came out of a NIH-driven initiative to try and improve the description and characterisation of a wide spectrum of dengue cases, for the purposes of research rather than just for clinical use.

What does the index capture in terms of the large differences in types of dengue infection?

Severe dengue is really the tip of the iceberg when it comes to dengue cases; the largest part of dengue infections may go completely unnoticed as many people can be asymptomatic and don’t experience any clinical ailments. There is also a very large proportion of patients who will experience some illness, but this won’t be clinically relevant, and they can still function normally and engage with work and school for example; they will likely not even seek treatment. The next smaller category will be those with classic dengue fever symptoms such as fever, a rash, bone pain and feeling unwell. And finally, the tip of the iceberg, the severe dengue cases, will

represent 2-4% of all dengue infections and are usually those infected for a second time with a different strain of dengue. So the co-authors and I are trying to describe a spectrum of dengue illness to address the fact that a very large segment of dengue illness was largely remaining ignored.

However, this silent majority is just as concerning from a public health point of view than the smallest and most severe segment because most of the people with these milder dengue symptoms are being managed as outpatients in dengue-endemic regions, which are largely in the developing world. But being managed as an outpatient doesn’t mean that those patients aren’t placing a burden on the health system – they represent a significant burden in terms of disability adjusted life years or other metrics. For example, if a child is not admitted to hospital but stays home, this still means she is missing school and an adult must stay home and miss a day of earning; they might be bringing the child back and forth to healthcare providers etc.

So when you take the number of non-severe but clinically relevant dengue cases and start layering all those potential impacts, it really does add to a public health burden. If you don’t have a way to measure that, then it’s possible that the true potential public health benefits of vaccines, drugs and other counter measures aren’t being fully measured. So while lots of work was being done on severe dengue, Bob and I wanted to work on dengue infection signs in a much more meaningful way for less severe dengue and that was the motivation behind starting the work and publication that you saw.