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We have recently found out that a cordon sanitaire has been implemented at airports, particularly aimed at flights from Wuhan, China, where passengers’ body temperatures are measured to assess whether they are infected by the coronavirus.

But is a body temperature screening at airports really a sufficient way of curbing the epidemic? Let’s find out together.

The principle behind the decision to carry out a body temperature measurement as a screening test is: “If everyone infected with the coronavirus has a fever, everyone infected by the virus can be identified if their body temperature is measured.”

Let’s try to shed some light on the matter. A person arriving from Wuhan airport may or may not have a fever, and may or may not be infected with the coronavirus. We put these two possibilities on the table. 

For the rows of the table, we put whether or not a person has the infection, ie when the person has acquired the virus, while in the columns of the table we put whether the person manifests a fever as a symptom or not. 

 

Infection / Fever Fever YES Fever NO
Infection YES
Infection NO

 

Now, let’s cross-reference the data from the rows and columns: Four possibilities are formed: 

  1. The person has a fever and the infection. 
  2. The person doesn’t have a fever and doesn’t have the infection
  3. The person has a fever but doesn’t have the infection
  4. The person doesn’t have a fever but has the infection

 

Infection / Fever Fever YES Fever NO
Infection YES Fever YES, Infection YES Fever NO, Infection YES
Infection NO Fever YES, Infection NO Fever NO, Infection NO

 

If the test was perfect, the result should be that everyone who has a fever also has the infection, and that those who don’t have a fever, do not have the infection. 

Well, as expected, a person who has a fever can possibly NOT have the infection as in the case of someone who has the normal flu and not the coronavirus. This case is called a FALSE POSITIVE. Because identified as having a fever, the person would be stopped, isolated, or subjected to a blood test for the coronavirus, but results would come out as NEGATIVE.

But can it also happen that a person infected with the coronavirus does not manifest a fever? Of course. This case is called a FALSE NEGATIVE. This is an individual who is NEGATIVE in having fever, but is FALSE as negative because he is positive for the virus.

All tests in medicine aim to have no false-negatives because these do not allow identification, with certainty, the people positive to the infection itself. 

In the case of the coronavirus, the ability of the screening test not to have false negatives is NOT OPTIMAL, in fact, it is rather poor!

In particular, it is estimated that the Incubation period, the duration in which there are no symptoms, can be between 1 to 14 days. This means that during the incubation period, the person is infected but has no symptoms, therefore no fever either.

As of today’s recent news, it seems that those infected are able to transmit the virus even during the incubation period when the person has no symptoms yet.

Therefore, it appears that symptom search tests, such as measuring the body temperature , are not effective in identifying all infected subjects, and thus the probability of infection is still high. 

 

Med4Care Marco De Nardin

Dr. Marco De Nardin