Fever is probably the oldest recognized sign of disease. Its study, description and interpretation dates from the earliest manifestations of civilization. And yet, today we lack common criteria to define the border of febrile temperature and its clinical management .

We are so used to live with mild diseases that course with fever that domestic diagnosis and self-management with OTC medications, like paracetamol or ibuprofen, is in our daily lives.
Fever in the hospital environment is a different issue, as it can be the sign of much more severe threats of health or even life. Nosocomial infections (hospital acquired infections) are severe, difficult to treat and overcome conditions.

When fever is high, especially when the onset is abrupt, the shivering, the prostration and discomfort along with just touching the patient will deliver a clear diagnosis. When we need to detect fever early and when fever is not so high, before the symptoms are clear, we need a reliable, sensitive, accurate thermometer.

Thermometry is key in the early detection and treatment of these diseases and other that represent co-morbidities of conditions that require stays in hospitals.

Thermometry has two objectives: solve the question, fever yes or not, and quantify it to let us know how severe it is. Ultimately, we need to take a clinical decision, to treat or not and how.

Thermometry has diverse technological solutions that are valid and that have reached long ago, most of them, the character of standard of care (SOC). This is the case of axillary, oral, tympanic and temporal artery among the non or minimally invasive. Rectal, pulmonary artery, esophageal and bladder thermometry are invasive methods reserved for the cases that need a monitoring. Rectal is the less invasive method and most commonly used among them and is frequently considered the gold standard in many thermometry studies.

Comfort and distress. Through this long-lasting daily relationship with fever and thermometry, we have developed a sense of comfort with the diagnosis of fever, as it is a “given” that using any of the SOC thermometers anyone, from health care professionals to lay-people at home, anywhere, at home, school or hospital, any time can “solve” the question, fever yes or not.

In the midst of this “comfort” COVID19 showed up and came to disrupt many comfort zones of our civil and medical life. Thermometry was one of them. Widely needed and, more than that, mandated as a screening method for the disease in the most unusual places (restaurants, airports, shops, dental offices, etc.), we had to rush to get a thermometer everywhere.

New Players. The number of suppliers soared in response to the high demand and new non-contact methods came to promise a hygienic and fast screening of febrile patients. These non-contact methods are mainly IR guns, thermographic screens and cameras; they had a speedlight adoption in the marketplace provided the apparent ease of use, being even passive and not needing a user needed to get the readings. All of them, along with the many new suppliers of SOC methods, were granted automatically the accuracy needed to detect fever effectively.
We have learned 3 key lessons in the past 2 years. And we have yet to learn and question some important matters regarding fever and thermometry.

  1. The incorporation of initial febrile screening, along with hygienic and social distancing measures are proving to be beneficial beyond the course of COVID19 pandemic. Endemic hospital based infectious diseases are pointing to a significant decline
  2. Not all thermometers are made equal. Among the SOC methods, not all products have the same reliability. Unfortunately, in the rush for supplies many new suppliers have failed to meet the minimal accuracy requirements. Some countries have been forced to review the way they award the quality certification, tightening the requirements, which has reduced significantly the suppliers that made the cut.
  3. Not all methods are valid. The new clinical application of non-contact IR guns have flooded the markets. Screening for early stages of fever call for a high sensitivity, the capacity of a diagnostic tests to avoid false negative results. The non-contact IR guns have been reported in one of the best and most recent studies to deliver a sensitivity of 60.5%. The FDA has recommended these thermometers not to be used for fever screening.
  4. All suitable methods can be misused. Most of SOC methods have a degree of user-dependence. This means that users can produce different readings of the same temperature in relation of how well they use the instruments. Workflow pressure, overconfidence or poor knowledge of the techniques can, and actually deliver, poor results. User dependent variability should be careful reduced with any method, from the most challenging ones (tympanic) to the easiest ones (temporal artery)

It is time to solve some pending matters.

We need to get a better reliability in the measurement of thermometry by choosing the methods that have the highest accuracy and less user dependent variability.

Good thermometry is not a given; it requires rigorous attention to the way we measure temperature. A thorough and universal training on the use of thermometers is of the essence to achieve the needed diagnostic accuracy of this fundamental vital sign .

We need better, more universally accepted guidelines and recommendations for fever diagnosis and management. Fever is indeed a natural reaction to disease that has a role in the natural fight to the disease but it can produce problems in itself and we need to have clear criteria when to treat and how.

In order to foster better guidelines, we need better, updated studies like the one on non-contact IR but that assess the SOC methods solidly. The scientific literature on clinical assessment of the different SOC thermometry options is very diverse methodologically, which makes it difficult to perform high impact metanalysis. Part of the methodologic issues is the fact that inter and intra-observer variability is not reported and taken into account in any of the available studies. As a consequence, there are different evaluations of the methods. There is a need for sound studies that assess with precision the SOC options in order to establish clear criteria for fever, understand the best way to use each one of them and their role and best indications in the different clinical settings.

Thermometry options comparison

Here is a summary of comments on the key features and benefits of the main clinical thermometry options.

The ideal clinical thermometer has to meet the following conditions:

  • Safe. This includes the risk of damaging through the use of the instrument and the hygienic considerations.
  • Easy to use. This is related with the good reproducibility of the results with a low variability
  • Comfortable for the patient. Patients’ comfort is frequently disturbed by clinical maneuvers, adding to the natural discomfort of their conditions. This is especially important in pediatric patients.
  • Non-invasive. Many “non-invasive” SOC methods have in fact some degree of invasiveness, ranging from the tympanic thermometers, to the non-contact IR guns. Deep thermometry methods that access through natural orifices are considered invasive (rectal, bladder, esophageal).
  • Fast. Workflow optimization of nursing staff is of the essence given the relative scarceness of the RN personnel and the increasingly high demand for care, let alone the pandemic crisis.
  • Precise. Clinical decision making has to be as early as possible in the course of disease and adequate. Vital signs quality is key for a fast and accurate decision making.
  • Cost-effective. Cost of use and cost of ownership are frequently a “hidden” part of the iceberg cost. Very small expenditure with a very high frequency will represent a surprisingly high annual cost (disposables) on one side. The repair and replacement cost due instrument fragility, fatigue or low quality is the second component of the ownership cost.