Temperature checks have become the new normal in airports, offices and even some residential buildings as authorities rush to contain the spread of the deadly new coronavirus , but medical and public health experts have said they are unlikely to detect infected people. Covid-19, the disease caused by the coronavirus, had sickened more than 91,000 people and killed over 3,100 worldwide as of Tuesday. Are ‘temperature guns’ reliable and accurate? Handheld, non-contact infrared thermometers, or “temperature guns”, have emerged as a popular device to screen people for fevers during viral outbreaks. Although the guns can quickly measure surface temperature without touching people’s skin, experts said using non-contact devices to avoid spreading the infection meant some accuracy was sacrificed . “In general, the remote infrared thermometers have been shown to be less reliable,” James Lawler, associate professor of medicine at the University of Nebraska, said. “As with skin contact thermometers, there are issues including sweating and heat loss that can affect temperature readings.” He said that electronic ear thermometers and oral thermometers may be more accurate but temperature readings would take more time and pose a higher risk of cross-contamination. “Contact is not a good idea for infection control, even with disposable covers,” Raina MacIntyre, professor of global biosecurity at the University of New South Wales in Sydney, said. How effective are temperature checks at detecting Covid-19? Thermometer guns and thermal screening cameras, which measure the heat coming off a person, will not catch everyone infected with Covid-19, because there are some who are infected but show no symptoms, according to experts. “People who are asymptomatic are just as likely to be contagious as those who have a fever or other symptoms,” MacIntyre said. Doctors warn China coronavirus carriers may show no symptoms of illness Research published in The New England Journal of Medicine last month showed two of 126 people evacuated to Frankfurt in Germany on a flight from China’s Hubei province had tested positive for the coronavirus after arrival despite passing symptoms-based screening before boarding the plane. The German researchers said this suggested that transmission “may occur in persons who have no fever and no signs or only minor signs of infection”. Additionally, an infected person may still be in the incubation period – the length of time between exposure to an infection and the appearance of the first symptoms. The US Centres for Disease Control and Prevention said Covid-19 symptoms may appear as soon as two days or as long as 14 days after exposure. But leading Chinese respiratory expert Zhong Nanshan last month warned that the incubation period could be as long as 24 days in rare cases. The 14-day mark is the World Health Organisation’s advisory period for monitoring cases and is based on data from other coronaviruses. Coronavirus contagious even in incubation stage, China says “Even if they have a Covid-19 illness with fever, they may not have a fever at the time they are screened due to the natural fluctuation of the fever or the use of medicines to bring the fever down,” said Sanjaya Senanayake, an infectious diseases specialist at Australian National University Medical School in Canberra. Last month, British researchers showed that temperature checks at airports can fail to detect a Covid-19-infected passenger in almost half of cases, in a study published in scientific journal Eurosurveillance . Screening at airports works only if transmission of infection by asymptomatic people is negligible, screening sensitivity is almost perfect and the incubation period is short, the report of the study said. Sense of security? Michael Osterholm, director of the Centre for Infectious Disease Research and Policy at the University of Minnesota, said temperature checks can provide a sense of security, but whether they are effective is a different story. “It’s clear that even with what was put into place, with border control, restricting travel between countries, temperature checks haven’t stopped [the spread of the virus],” he said of the arrival of the virus into the United States. “[A sense of security] is all it is, if you look at how many people have actually been identified and diverted by those temperature checks.” However, other countries have identified infected people at travel checkpoints. The first Covid-19 case outside China, a 61-year-old Chinese woman from Wuhan who travelled to Bangkok, was detected by thermal surveillance at Suvarnabhumi Airport on January 13. Osterholm compares it to other measures with similar purpose. “The same thing is true with disinfectant,” he said. “There is television footage of people out there spraying, and we don’t have any evidence that it makes any difference at all in disease occurrence.” Additional reporting by Simone McCarthy Purchase the China AI Report 2020 brought to you by SCMP Research and enjoy a 20% discount (original price US$400). This 60-page all new intelligence report gives you first-hand insights and analysis into the latest industry developments and intelligence about China AI. Get exclusive access to our webinars for continuous learning, and interact with China AI executives in live Q&A. Offer valid until 31 March 2020.