London School of Hygiene & Tropical Medicine

Airport screening for infectious disease such as Ebola, bird flu and SARS will often miss half or more of infected travellers, but can be improved, according to new researched published in the journal eLife.

One of the biggest barriers to success is the lack of honest reporting by passengers about their risk of exposure, if being honest could put them at risk of delay.

Researchers from the London School of Hygiene & Tropical Medicine and the University of California, Los Angeles (UCLA) have identified ways to make current screening as effective as possible and highlighted what needs to be done next to improve it further.

The study presents options for policy makers, including whether resources would be better spent on arrival screening which will reduce but not eliminate the cases, or on tracing and containing potential cases highlighted by airport questionnaires.

Using a mathematical model to analyse screening for six viruses – SARS coronavirus, Ebola virus, Middle East respiratory syndrome coronavirus (MERS-CoV), Marburg virus, swine flu (H1N1), and bird flu (H7N9) – the researchers found that for diseases with a long incubation period such as Marburg and Ebola, taking passengers’ temperature to test for fever is particularly ineffective at the start of an epidemic.

The findings suggest that for the early phase of these disease epidemics, questionnaires are the most effective detection method.

With diseases such as swine flu that take a shorter time to incubate, fever screening was found to be the most effective method throughout an epidemic.

Fever screening on arrival has previously been criticised for being particularly ineffective, but the researchers found it can catch some cases missed at departure. The findings suggest infrared non-contact thermometers will only ever pick up fevers at most 70% of the time. Also, symptoms of some diseases will progress during transit so can be easier to detect on arrival.

Understanding how each disease progresses can improve detection by making sure the right questions are asked in questionnaires. For example, exposure to a symptomatic patient is an established risk factor for contracting Ebola.

However, the researchers found that at best 25% of people honestly reported on exposure to influenza during the 2009 pandemic, and some might even have hidden symptoms by taking medication. This is the first time available information has been used to arrive at an estimated figure.

Study co-author Dr Adam Kucharski, Research Fellow in Infectious Disease Epidemiology at the London School of Hygiene & Tropical Medicine, said: “Our findings show that airport screening must be tailored to the outbreak in question. The effectiveness of departure and arrival screening will depend on the pathogen, the screening method used, and the current state of the epidemic. For example, questionnaires about potential exposure would be unlikely to catch MERS-CoV cases, but might be useful for other infections. Fever screening at arrival might pick up some influenza A/H7N9 cases, but would be unlikely to spot many Ebola infections.

“There is no one-size-fits-all solution. Screening can be expensive and inconvenient, and it is important to provide a scientific case for it, rather than just political one.”

The research was supported by the National Institutes of Health and the National Science Foundation in the US and by the Medical Research Council in the UK.

• Katelyn Gostic, Adam Kucharski, Jamie Lloyd-Smith. Effectiveness of traveller screening for emerging pathogens is shaped by epidemiology and natural history of infection. eLife. DOI: 10.7554/eLife.05564