Redefining fever

Fevers are tough.  They make you feel lousy.  They cause worry.  They prevent kids from attending school and adults from going to work.

But they’re also tough for doctors.  Patients with fevers always present a challenge. What’s causing it? Is it a virus that will go away on its own? A bacterial infection that requires antibiotics?  Does the patient need to be admitted to the hospital? Or does the fever herald something more ominous?

Recurrent fevers

As a rheumatologist specializing in autoinflammatory diseases, many of the patients that I see–both kids and adults–complain of fevers.  Some have had years of fever episodes that recur like clockwork.  Others have persistent fevers for weeks or months that haven’t gone away.  Many have seen countless doctors, received multiple diagnoses, only to have those diagnoses recanted after negative tests or failed treatments.

Autoinflammatory diseases are rare illnesses that cause unprovoked episodes of fever and systemic inflammation.  That is, they activate the body’s immune system–which usually works to combat infections–but in the absence of any pathogens.  This can cause a variety of symptoms including body aches, joint pain, skin rash, enlarged glands…rarely they can affect the brain and other internal organs.  Most autoinflammatory diseases are genetic, but many have no known cause.

In clinic, as I sit in the room and listen to the patient’s story, I sometimes feel like Sherlock Holmes, looking for patterns and clues that will help me solve the crime–I mean–identify the fever’s underlying cause.  Are fevers always accompanied by stomach aches and chest pain?  Do fevers last more than a week?  Are patients well between episodes? Is the child growing appropriately? Is the woman losing weight?

As I said before, fevers are tough. After taking a full medical history and examining the patient, I often struggle, like many doctors before me, to give the patient a firm diagnosis. Most patients don’t usually have a fever on the day they see me, and from their history, it’s challenging to discern whether their fevers are caused by rare autoinflammatory diseases or by repeated infections (infections are the most common cause of recurrent fevers).

The problem

Was there a better way of distinguishing the cause of the fever? Could we somehow look at the fever pattern of their illness, and from it, identify the underlying cause?

As I began to research this question, I found out that doctors have a rudimentary understanding of temperatures.  For instance, the idea that normal body temperatures are 98.6 F (37C) and that fevers are 100.4 (38C) stem from one study done by Carl Wunderlich in 1868, and its findings have rarely been questioned.  A few brave souls have challenged Wunderlich’s findings, noting that his thermometer was inaccurate and that he may have overestimated actual temperatures.  Smaller studies have suggested 98.2F (36.8F) is a more “normal” temperature, although it varies depending on the time of day, with lower temperatures in the morning, and higher temperatures in the afternoon.

From Wunderlich's "On the Temperature in Diseases," 1868.
From Wunderlich’s “On the Temperature in Diseases,” 1868.

In addition, most doctors view temperature as binary–you either have a fever or you don’t.  But what if my temperature is 99 F, when my normal is 97 F?  Does that not mean anything?   Could it indicate that I have an infection? Could it reflect the fact that my arthritis was active?  Could the temperature indicate that my lupus was acting up?

With these thoughts in mind, I was determined to conduct a study to answer these questions.  I wanted to take Wunderlich’s studies into the 21st century and redefine what fevers are all about.

The solution

Two technological breakthroughs have made it possible to significantly improve upon the work that Wunderlich conducted.  First, we now have wearable thermometers that continuously measure your temperature, similar to how the Apple Watch or Fitbit tracks your heart rate  This gives us an unprecedented amount of detailed information that may provide us with a way to identify fever patterns specific for various ailments.

The second breakthrough is the development of crowdsourcing technologies that allow large numbers of people to contribute their data for research.  Apple recently launched ResearchKit, which allows anyone with an iPhone to join a research study and contribute their health data for science. Patients from across the country are now empowered to become partners in research, rather than subjects to be studied.


With colleagues from the Autoinflammatory Clinic and Innovation & Digital Health Accelerator at Boston Children’s Hospital, we created Feverprints, a research study about temperatures in health and disease. By downloading and signing consent, users can anonymously contribute their temperatures when they are well, which will allow us to redefine what “normal” temperatures are. We may find that no single “normal” temperature exists, and that, in fact, it varies with time of day and between people of different ages, sexes, ethnicities, and sizes.   If this is the case, we will develop algorithms to help doctors interpret temperatures more accurately.

Feverprints screenFeverprints

We are also interested in tracking temperature when people are ill.  We are looking to discover fever patterns (“feverprints!”) that are specific for various diseases. Identifying these feverprints may allow doctors to make faster and more accurate diagnoses.

Finally, we want to learn about the effect of fever medicines (like Tylenol or Motrin) on a variety of illnesses illness.  Do these medicines actually help to lower body temperature? Do they make people feel better? Do they help people to heal faster, or does it actually allow the infection to persist for longer periods, as some studies have shown?

Next time I see a patient in clinic with recurrent fevers of unknown cause, I hope to be able to use the information we gain from our Feverprints study to provide her with a timely and accurate diagnosis and offer her effective treatment.  Will you help make this happen?


I invite you to learn more about our Feverprints study. I hope you are able to help us better understand what fevers are all about.  You can download the Feverprints app from Apple’s App Store.