Thermal Scanner – Credit Wikipedia
# 8118
As you might expect, today’s big story out of Taiwan (see Taiwan CDC Reports Second Imported H7N9 Case) has not escaped the notice of the public Health Officials in Hong Kong. The following statement has been posted on their http://www.info.gov.hk website, which also contains details on Hong Kong’s border security measures designed to identify and isolate potential carriers of the virus.
First, the statement, then I’ll return with a bit more on the value and history of thermal screening for disease.
CHP closely monitor a human case of avian influenza A(H7N9) in Taiwan
The Centre for Health Protection (CHP) of the Department of Health (DH) tonight (December 31) noted a confirmed human case of avian influenza A(H7N9) affecting a man aged 86 in Taiwan.
The patient, who lives in Jiangsu Province in Mainland China, travelled to Taiwan on December 17. He had onset of symptoms including loss of appetite and chest discomfort since December 19. He sought medical consultation from a local hospital on December 24. His specimen tested positive for the avian influenza A(H7N9) virus upon testing by the health authority in Taiwan today. He is currently admitted for further management.
"Locally, enhanced disease surveillance, port health measures and health education against avian influenza are ongoing. We will remain vigilant and maintain liaison with the World Health Organization (WHO) and relevant health authorities. Local surveillance activities will be modified upon the WHO's recommendations," a spokesman for the DH remarked.
All border control points (BCPs) have implemented disease prevention and control measures. Thermal imaging systems are in place for body temperature checks of inbound travellers. Suspected cases will be immediately referred to public hospitals for follow-up investigation.Regarding health education for travellers at BCPs, distribution of pamphlets, display of posters in departure and arrival halls, in-flight public announcements, environmental health inspection and provision of regular updates to the travel industry via meetings and correspondence are all proceeding.
"Travellers, especially those returning from avian influenza A(H7N9)-affected areas and provinces with fever or respiratory symptoms, should immediately wear masks, seek medical attention and reveal their travel history to doctors. Health-care professionals should pay special attention to patients who might have contact with poultry, birds or their droppings in affected areas and provinces," the spokesman advised.
Hong Kong has recently seen two imported cases of H7N9 themselves, and with the traditional peak of the `bird flu season’ still ahead, finds itself – like Taiwan – is very much on the front lines against this emerging virus.
Since fever is often a hallmark of infection, thermal imaging has been promoted as a way to protect the public and (hopefully) delay introduction of a virus into a country during a pandemic. Unfortunately, these checks haven’t produced much in the way of compelling results in the past.
The problem is, not everyone who is infected will exhibit a fever.
- Some may be silently incubating the virus, and will become symptomatic in another 24-48 hours
- Others may have other symptoms, but no fever
- Some may be taking antipyretics (fever reducers) to ease symptoms or evade detection
- And some may simply be asymptomatic carriers of the virus.
Added to these, scanners can be foiled by other factors including the consumption of hot beverages or alcohol, pregnancy, menstrual period or hormonal treatments. All of which can increase the external skin temperature and cause a false positive.
Inversely, intense perspiration or heavy face make-up can have a cooling effect on the skin temperature which can cause a false negative.
Over the years we’ve looked at a number of thermal screening studies that have tried to quantify their value. A few highlights include:
In April of 2012, in EID Journal: Airport Screening For Pandemic Flu In New Zealand, we looked at a study that found that the screening methods used at New Zealand’s airport were inadequate to slow the entry of the 2009 pandemic flu into their country, detecting less than 6% of those infected.
Unlike some other countries in 2009, New Zealand did not employ thermal scanners, which look for arriving passengers or crew with elevated temperatures. But even countries that employed thermal scanners and far more strict interdiction techniques during the summer of 2009 failed to keep the flu out.
Since there is nothing worse than being sick away from your own country and your own doctor, to little surprise in Vietnam Discovers Passengers Beating Thermal Scanners, we saw evidence of flyers taking fever-reducers to beat the airport scanners in order to get home.
In December of 2009, in Travel-Associated H1N1 Influenza in Singapore, I wrote about a a study in the CDC’s EID Journal entitled: Epidemiology of travel-associated pandemic (H1N1) 2009 infection in 116 patients, Singapore that determined that airport thermal scanners detected only 12% of travel-associated flu, and that many travelers boarded flights despite already experiencing symptoms.
And in June of 2010 CIDRAP carried a piece on a study of thermal scanners in New Zealand in 2008 (before the pandemic) presented at 2010’s ICEID called Thermal scanners are poor flu predictors.
None of which is to suggest that Hong Kong shouldn’t try to interdict infected travelers at the border, because even if the success rate is low, there may be some value in trying to limit the number of infected persons arriving into a country, particularly during the opening days and weeks of an outbreak.
But no one should be over-comforted by the thought of thermal scanners deployed at borders or airport terminals, as their impact on the spread of any infectious disease is likely to be limited.
