Temperature checks, like this being performed at the Bratislava-Jarovce border crossing between ... [+] Austria and Slovakia, may catch some cases of Covid-19 coronavirus infections but far from all.. (Photo by JOE KLAMAR / AFP) (Photo by JOE KLAMAR/AFP via Getty Images)

It may help determine whether you want more cowbell. But a fever is not a great way to tell if you have a Covid-19 coronavirus infection.

One problem is that you may not be hot (in a temperature sense, that is) yet still have the Covid-19 coronavirus. A study published on July 6 in the Proceedings of the National Academy of Sciences (PNAS) estimated that when someone gets infected with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV2), over 50% of the time the person who gave him or her the virus did not have any symptoms when the transmission occurred. And a recently published study in the Centers for Disease Control and Prevention (CDC) Morbidity and Mortality Weekly Report (MMWR) revealed that 20% of a convenience sample of 164 patients with Covid-19 and symptoms did not happen to have a fever. So, doing the math suggests that less than 40% of people who are contagious will have a fever.

A second problem is that you may be hot (again, from a temperature sense) yet not have the Covid-19 coronavirus. A wide range of different things can cause a fever besides cowbell-deficiency. A fever can result from many other infections including the flu, hepatitis, malaria, and norovirus as well as inflammatory diseases such as rheumatoid arthritis or Crohns disease. A fever can occur when you are teething, assuming that you are an infant. (First, check if you are an infant. If are not an infant, yet teething, see your dentist as soon as possible.) Blood clots, particular medications, a bad sunburn, and food poisoning are other possible culprits.

Physical activity could raise your body temperature. (Photo: Getty)

Then theres the problem of being hot some of the time. Your physical activity and the temperature of the air around you can affect your body temperature. Therefore, going jogging in a sauna while wearing a parka prior to a temperature check could push up your reading.

Your body also may have natural fluctuations in temperature. A study published in the Journal Chronobiology International revealed that body temperature can vary over the day, the week, and the year. Each day, body temperature tends to be lowest between 6 and 8 am and highest between 6 and 8 pm. So, having a hot dinner or a hot dinner date may have more than one meaning. Body temperature is typically slightly colder in winter compared to the summer as well.

Other things can naturally affect your body temperature too. Just look at the study published in Biological Rhythm Research that measured the oral temperature of a woman every evening for, get this, 30 years. Her body temperature varied with her menstrual cycle, decreased as she aged, and declined significantly during menopause. Her temperature went up and down with the seasons too, peaking in August and bottoming out in FebruaryMarch.

A fourth problem is being hot but hiding it. Say you take a fever-reducing medication like Tylenol for some other reason such a headache, toothache, or hearing someone tell you how great he is during a speech. This medication could mask any fever that you may have.

Another problem is people not being able to tell that you are hot. Body temperature measurements could be wrong. As they say in real estate, location, location, location. Where you stick the thermometer can affect the temperature reading registered. If you are measuring your temperature on your knee, you dont know what you are doing. More common locations are your ear, rectum, mouth, and armpit, not necessarily sequentially and not in that order. A systematic review published in the Annals of Internal Medicine in 2015 showed that rectal temperatures give the most accurate readings compared to those other locations.

Of course, rectal temperature screening at say a campaign rally or a restaurant may not be the easiest thing to do logistically. Therefore, a business or organization may opt for less anal, so to speak, methods of measuring temperature. They may even utilize non-contact approaches such as thermal imaging systems and infrared thermometers because taking temperatures through touching many different people may not be the best thing to do these days.

A thermal camera checks the body temperature at Manuel Mrquez de Len airport on July 17, 2020 in ... [+] La Paz, Mexico. (Photo by Alfredo Martinez/Getty Images)

Keep in mind though such non-contact devices could vary significantly in accuracy. After all, as the saying goes, the further you get from the rectum, the less accurate things become. Plus, surprise, surprise, people may not follow directions. As I mentioned back in February for Forbes, if people need directions to toast a Pop Tart, you can imagine how they may screw up using a temperature taking device. Thats essentially the warning thats on a U.S. Food and Drug Administration (FDA) website: These devices have many benefits, but they must be used properly to get accurate readings. Since an elevated temperature does not conclusively indicate a Covid-19 infection, further evaluation and diagnostic testing are needed to determine if someone has a Covid-19 infection.

All in all, temperature screening may catch some cases of the Covid-19 coronavirus. But it could miss many others. Thus, be skeptical whenever anyone tries to assure you that things are safe just because they are doing temperature and symptom screening. For example, Nina Shapiro wrote recently for Forbes about how daily temperature checks will not be enough for kids to return to school.

Remember preventing the spread of the Covid-19 coronavirus requires a combination of interventions that must include social distancing. The use of temperature and symptom screening will not obviate the need to keep people more than six feet apart and to do other things such as actively disinfecting surfaces and having everyone wear masks. One intervention is never going to be enough. Christopher Walken may have said on Saturday Night Live, "I've got a fever and the only prescription is more cowbell. But that didnt mean that he didnt want to hear the rest of the band as well.

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Why Fever, Temperature Checks Are Inaccurate Ways To Screen For Covid-19 Coronavirus - Forbes