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Twice Daily Temperature Checks at Home – What You Need to Know

In these times of COVID-19, checking for fever in the morning is not the most accurate time to detect a fever. Our daily circadian rhythm regulates our body temperature, which is lowest in the morning, and highest in the evening. New research shows this happens with fevers as well.

Up to 50% of fevers are missed in the morning, but none are missed in the evening due to circadian effects, making dinner time a good time for a second daily scan. Twice daily morning and evening fever detection is the best defense at home.

Questions and answers below are taken from the Northeastern University School of Nursing Virtual Summer Academy 2020 Presentation on Temperature Assessment by Dr. Marybeth Pompei, Senior Vice President and Chief Clinical Scientist Exergen Corporation and Affiliate Professor at Northeastern. Questions were posed by the Dean of the School of Nursing, and answers and recommendations provided by Dr. Pompei, as an expert in this field. 

 

Q&A’s on Temperature Screening

Q: What are the recommendations from authorities for temperature screenings to be done at home?

A:

American Academy of Pediatrics (AAP) School Guidelines

“Testing & temperature checks. The CDC currently does not recommend COVID testing of students and staff. Testing only shows whether a person is infected at that specific moment in time and may not be useful in preventing outbreaks in school communities. Taking students' temperatures at school may also not be feasible, but you can monitor your children's health at home and keep them out of school if they are not feeling well and have a fever. Schools should frequently remind students, teachers, and staff to stay home if they have a fever of 100.4 degrees F or greater or have any signs of illness.”
Check out this article on Returning to School During COVID-19

Centers for Disease Control and Prevention (CDC)

Massachusetts Department of Elementary and Secondary Education

“Checking for symptoms each morning by families and caregivers is critical and will serve as the primary screening mechanism for COVID-19 symptoms.41 Schools should provide information to families in their primary language to support them in conducting this symptom check and families should not send their children to school if they exhibit COVID-19 symptoms. We will be providing a checklist of symptoms and other guides to districts and schools to help families and students.

*Screening procedures are not required at the point of entry to the school. However, school staff (as well as bus drivers) should observe students throughout the day and refer students who may be symptomatic to the school healthcare point of contact.

*As noted in previous guidance, temperature checks are not recommended as screening for all students due to the high likelihood of potential false positive and false negative results.”

Q: How do circadian rhythms impact temperatures and assessments of temperatures?

A: Our internal biological clocks produce circadian cycles that vary throughout the 24 hours of each day. This causes body temperature to vary about 1.6°F (0.9°C) between lowest temperatures in the morning and highest temperatures in the evening. With fever, the circadian variation still occurs, but at higher temperatures.


Accordingly, temperature assessments in the morning are low and will miss about half of the fevers. Temperature assessments in the evening are high and will detect all the fevers.


Mornings Not Ideal for Fever Screening. NYTimes/Reuters, May 27, 2020

“Morning fever screenings may be misleading.
As businesses and cities reopen, screening people for fever when they arrive in the morning at work or school is likely to be widely used to help prevent coronavirus spread. But “morning may be the worst time” to screen for fevers, researchers say. They draw this conclusion from data collected from more than 300,000 people during studies of flu outbreaks in earlier years. “Fever-range temperatures… were rarest during mornings, and were about half as common during mornings as during evenings in periods of high influenza activity,” they report in a paper published on Tuesday without peer review on the medRxiv preprint server. “The results suggest that morning temperature measurements could miss many febrile disease cases,” they said.” (Read the Article)

Recent Published Studies on Circadian Effects on Fever

Harding et al (2020). Fevers Are Rarest in the Morning: Could We Be Missing Infectious Disease Cases by Screening for Fever Then? Undergoing peer review at https://doi.org/10.1101/2020.05.23.20093484

Harding et al (2020). Fever incidence Is Much Lower in the Morning than the Evening: Boston and US National Triage Data. West J Emerg Med. 2020 Jun 24;21(4):909-917. doi: 10.5811/westjem.2020.3.45215. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7390559/

Harding et al (2019). The daily, weekly, and seasonal cycles of body temperature analyzed at large scale. Chronobiol Int. 2019 Dec;36(12):1646-1657. doi: 10.1080/07420528.2019.1663863. Epub 2019 Sep 17. https://publishingimages.s3.amazonaws.com/eZineImages/PracticePerfect/706/The_daily_weekly_and_seasonal_cycles_of_body_temperature.pdf

Q: When do you recommend that temperatures be taken for school-aged youth?

A: Twice Daily. Before leaving for school in the morning, and at dinner time in the evening. If a fever is detected at either time, the student stays home and parents should contact their medical care professional immediately. 

 

Even if the student is learning on-line, it is important to check temperature twice daily for the sake of the health of students and family members.


Q: What makes thermometers accurate? What should we know about thermometer accuracy?

A: Published peer-reviewed clinical studies. Without such studies by medical professionals, there is no assurance of accuracy on children and adults in all settings.

Accuracy specifications by manufacturers of thermometers are laboratory accuracy, not accuracy in actual use on people being tested for fever. Laboratory accuracy tests do not include important physiological effects which vary from person to person, and setting to setting, which can affect the actual accuracy well beyond their laboratory accuracy.

Published peer-reviewed clinical studies are the gold standard for accuracy, since they include actual use on people in many settings, which automatically includes the physiological effects that vary from person to person and setting to setting. Only these studies can provide the assurance that the thermometer will provide accuracy in detecting fevers for all ages in all settings.

With more than 80 published peer-reviewed clinical studies attesting to the accuracy on all ages from newborns to geriatrics, in all settings where fever detection is needed, the Exergen Temporal Artery Thermometer is by far the most proven accurate, compared to thermometers which have no or very few clinical studies.

How about No Touch Thermometers?

No Touch thermometers are highly inaccurate for detecting fevers, here is why:

Accuracy specifications by manufacturers of No Touch thermometers are laboratory accuracy, not accuracy in actual use on people being tested for fever. Laboratory accuracy tests do not include important physiological effects which vary from person to person, and setting to setting, rendering No Touch thermometers unreliable, regardless of their laboratory accuracy. For No Touch devices, these physiological effects can overwhelm the normal laboratory accuracy of the device, to the point that its actual error is 2 deg C rather than 0.2 deg C.

   

Estimated standard deviation of temperature uncertainty

Physiological Variable

Est. Range

No-Touch Thermometry

TA Thermometry

Skin emissivity

0.97 ± 0.02

0.31°C

0.03°C

Skin ambient temperature

±5°C

0.58°C

0.06°C

Variable perfusion on face

±1°C

0.58°C

0.06°C

Perspiration on the face

±1°C

0.58°C

0.06°C

95% confidence interval of errors clue to identifiable skin physiological variables

2.09°C

0.21 °C

This discrepancy in accuracy was clearly observed during the SARS epidemic in 2003. Exergen, recognized as experts in this field, was asked to provide the underlying science in a study regarding this accuracy discrepancy at a Symposium in 2004, which was subsequently published. The chart above is from that published study, and shows that the errors due to physiological effects is +/- 2.09 deg C.,compared to the light contact method of temporal artery (TA) scanning error of +/- 0.21 deg C. The TA thermometer was specifically designed to overcome these physiological barriers to obtaining accurate readings, and were awarded numerous patents on the design. (Pompei and Pompei 2004). Subsequent studies confirmed the Pompei findings of 2004.

In 2009, Bitar et al. reviewed 6 studies of fever screening with non-contact infrared thermometry (NCIT) devices, such as thermometer guns and thermal imagers. Across the reviewed studies, the sensitivity of NCIT ranged from 4% to 90% and its specificity ranged from 75% to 100%. In other words, NCIT detected fever in from 4% to 90% of the people with fevers, and NCIT did not detect fever in from 75% to 100% of people who lacked fever. The extremely wide range of reported sensitivities (4% to 90%) suggests generally poor usefulness of the NCIT methods, both because values at the low end of the range are unacceptably poor (4% of fevers detected), and because it is difficult to recommend a technology for which the user cannot tell if they will receive good (90%) or disastrous (4%) performance. https://www.eurosurveillance.org/content/10.2807/ese.14.06.19115-en

In 2019, Mouchtouri et al. reviewed the real-world efficacy of fever screening at airports and borders, and found that almost no disease cases had been caught across several nations and pandemics. The screenings were primarily performed with thermometer guns and thermal imagers. https://www.mdpi.com/1660-4601/16/23/4638

It is now common knowledge in the professional medical community that No Touch thermometers are too inaccurate to use as a reliable screening device for fever, and are used largely for theater effects. An August 13, 2020 article in Forbes magazine quotes Dr. Anthony Fauci, director of the National Institute for Allergy and Infectious Diseases, as saying, when referencing infrared thermometers that take a person’s body temperature by aiming the device at their forehead, “We have found at the [National Institutes of Health] that it is much, much better to just question people when they come in and save the time, because the temperatures are notoriously inaccurate many times.

Without peer-reviewed published clinical studies, No Touch thermometers commonly available cannot be relied upon for medical accuracy in fever detection.

Q: What types of thermometers are recommended for use in schools? For use by families?

A: Only those that are clinically accurate as demonstrated by published peer-reviewed clinical studies.

For school nurses checking students that might be sick, a professional grade fast, accurate, non-invasive thermometer scanning the temporal artery with more than 80 published peer-reviewed clinical studies, is best.


For families, a home model thermometer that is fast, accurate, and non-invasive, scanning the temporal artery, backed by more than 80 published peer-reviewed clinical studies, is best.


Q: How is the cut-off for fever chosen?

A: 100.4°F (38.0°C) is the medically accepted definition of a fever for more than 100 years, is recommended by AAP, CDC and WHO, and used in every medical institution in the world.

Q: Can you explain how a thermometer margin of error might guide the choice for a cut-off of fever?

A: Some attempts to use a lower cut-off for Covid-19 screening have been made due to the low readings of the no touch thermometers from their inaccuracies. These attempts have been unsuccessful in “improving” the no touch devices’ accuracies. 

A thermometer with accuracy backed by more than 80 published peer reviewed studies requires no adjustment to the medical standard cut-off for fevers.

 

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Medical information disclaimer: this document may contain general information relating to various medical conditions and their treatment. Such information is provided for informational purposes only and is not meant to be a substitute for advice provided by a doctor or other qualified health care professional. Readers should not use the information contained herein for diagnosing a health or fitness problem or disease, and should always consult with a doctor or other health care professional for medical advice or information about diagnosis or treatment.