Swine flu: can it be stopped at the border?

Anyone looking at the news in the last couple of days can be of no doubt as to the leading story of the moment (well, at least it makes a change from the credit crunch). Over 100 deaths from swine flu in Mexico, confirmed cases in the USA, Canada and now Spain, and suspected cases in countries from New Zealand to Israel, have caused fears of a possible pandemic. But what can the world do to limit spread of the virus?

 

In modern times, the huge rise of international travel has meant that diseases can spread around the world far more rapidly than previously. And just as international travel can spread a disease round the globe in a matter of days, so the travel and tourism industry is highly vulnerable to the impacts of disease outbreaks. The best known case is SARS (severe acute respiratory syndrome), which had a dramatic effect on tourism in Asia. Thus an early effect of the current swine flu alert is heavy decreases in shares of airlines and tourism companies around the world, with shares in British Airways decreasing by 8% early this morning.

 

One result of the SARS epidemic, and of fears of a possible bird flu pandemic which have been prevalent in recent years, is that as well as huge stocks of antiviral agents, many countries have plans and equipment in place to institute border screening of travellers arriving from affected countries. This is particularly the case in Asia, where airport screening for passengers with elevated temperatures was instituted in many destinations during the SARS scare. In Hong Kong, where SARS killed hundreds of people in 2003, all travellers will be screened on arrival, and any ill person will be quarantined. Airport screening plans for arrivals from affected countries have also been announced by Japan, Singapore, Malaysia, South Korea and Indonesia. Australia is also on high alert, and Health Minister Nicola Roxon says some form of screening at Australian airports could be in place "in the next few days" amid fears of a global swine flu pandemic.

 

"The Government's crisis committee, the health committee, is meeting today to assess when and whether the new steps – including screening at airports – might be necessary," Ms Roxon said. "I think that it is likely that in the course of today or the next few days those steps may well be necessary.

 

"It's important for the public to be aware if they've been travelling in Mexico and the Americas, if they are feeling flu-like symptoms to see their doctors."

 

But how effective is border screening? Looking at a number of papers on the CAB Abstracts database and on public health news sites, the answer seems to be 'not very'.

 

To watch for disease without producing chaos and delays at airports and other border crossings, remote-sensing infrared thermography (IRT) has been advocated as a means for testing for fever. But with a high rate of 'false positives', and a delay of several days between infection and the occurrence of fever and other symptoms, the best evidence suggests that while screening can delay and reduce the number of cases from flu and other fevers, it is almost impossible for most countries to keep out a disease altogether (the exceptions may be cases such as small island nations, where it is easier to screen and keep track of all arrivals).

 

The most recent publication I can find is a paper on U.S. airport entry screening in response to pandemic influenza (Malone et al. 2009) published online by Travel Medicine and Infectious Diseases on 14 April. In a simulation model, it was found that in the first 100 days of a global pandemic, U.S. airport screening would evaluate over 17 M passengers with 800 K secondary screenings. 11,570 pandemic influenza (PI) infected passengers (majority asymptomatic) would enter the U.S. undetected from all 18 airports. It is concluded that while U.S. airport screening identifies 50% of infected individuals; efficacy is limited by the asymptomatic PI infected. Screening will not significantly delay arrival of PI via international air transport, but will reduce the rate of new US cases and subsequent deaths.

 

A recent French study (Bitar et al., 2009) also suggested that using temperature scanners in airports to try to identify and block entry of sick travellers during a disease outbreak is unlikely to achieve the desired goal. The authors, from France’s Health Watch Institute, said the available scientific data suggests there is little benefit to airport temperature screening when the incidence of disease is low, as it was with SARS and as it would be expected to be in the very early days of a pandemic.

 

“Because public perceptions are important, policy-makers may feel some pressure to use NCIT” — non-contact infrared thermometers — “but the decision making process should not ignore the poor scientific evidence on NCIT’s efficacy to delay the introduction of a novel influenza strain,” they wrote in a study published earlier this year in Eurosurveillance, the weekly infectious diseases journal produced by the European Centre for Disease Prevention and Control in Stockholm.

 

A 2004 study on Canada’s airport screening efforts showed that 4.6 million travellers were screened between May and November of 2003. Only 1,435 had an elevated temperature and none of those people had SARS (Health Canada, 2004).

 

Chan et al. (2004) evaluated the use of infrared thermography (IRT) to detect fevers in travellers at airports and border crossings and determined that IRT readings from the side of the face, especially from the ear at 0.5 m, yielded the most reliable, precise and consistent estimates of conventionally determined body temperatures. Samaan et al. (2004) report on the use of border screening for SARS in Australia, where a low identification rate was attributed to the low prevalence of SARS, the use of exit screening by affected countries, and the subjective measures used in the screening process. Glass and Becker (2006) suggest that border screening has a relatively minor role in reducing disease spread. For the case of SARS, it was suggested that screening can detect up to 10% (95% CI 3-23) of infected travellers, and reduce the probability of a large outbreak by up to 7% (95% CI 2-17).

 

While border screening is unlikely to prevent the spread of a disease such as SARS and influenza, if it delays the spread and reduces the number of cases, it may give national governments and health authorities a bit more breathing space to improve methods for detection and isolation of cases, and for other actions to limit the possibility of a pandemic. We don't yet have a pandemic, and it may be that we don't get one in this case. But whether or not we do, the short-term impact on travel and tourism (my particular area of focus, as editor of CABI's website on the subject, Leisuretourism.com) could be profound. Mexico's tourist industry, already suffering from the country's drug wars, is likely to be devastated at least in the short term. And today EU Health Commissioner Andorra Vassiliou has advised Europeans to reassess their travel plans to the America's.

 

She told reporters "they should avoid traveling to Mexico or the United States of America unless it is very urgent for them."

 

Whether or not we develop a pandemic – and it's important to stress that we aren't in one yet – the impact of swine flu on the economy and travel is already apparent.

 

Further reading

 

1.  Screening for fever by remote-sensing infrared thermographic camera. Chan LungSang , Cheung, G. T. Y. , Lauder, I. J. , Kumana, C. R. / Journal of Travel Medicine, 2004, Vol. 11, No. 5, pp. 273-279, 24 ref.
2.  Evaluation of measures to reduce international spread of SARS. Glass, K. , Becker, N. G. / Epidemiology and Infection, 2006, Vol. 134, No. 5, pp. 1092-1101, 15 ref.
3.  Thermal image scanners to detect fever in airline passengers, Vancouver and Toronto, 2003. Canada, Health Canada / Canada Communicable Disease Report, 2004, Vol. 30, No. 19, pp. 165-167, 7 ref.
4.  Border screening for SARS in Australia: what has been learnt? Samaan, G. , Patel, M. , Spencer, J. , Roberts, L. / Medical Journal of Australia, 2004, Vol. 180, No. 5, pp. 220-223, 14 ref.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s