At this writing SARS transmission has been stopped in most areas that had high grade local transmission and appears on the verge of interuption in all other areas. Despite these encouraging trends much (or most) about SARS remains unknown. It is too soon to say what patterns of transmission—endemic, periodically epidemic, or seasonal—will develop.
SARS cannot be controlled in the world if SARS cannot be controlled in China where the SARS coronavirus originated. It is not yet known whether China is capable of the necessary sustained public health response. The presence of a robust animal reservoir would counteract much of even the most efficient of efforts. Much of our globalised economy depends on China and its immediate neighbors. We cannot simply erect a wall around a region but must continue to rigidly adhere to already developed guidelines at the expense of some inconvenience to ease of international travel.
The international traveler is an efficient vector of SARS as well as new respiratory pathogens yet to emerge. A SARS like scenario was predictable. GeoSentinel is a global provider-based sentinel surveillance system of specialized travel and tropical medicine clinics that has been tracking infections in travelers since 1997 (www.istm.org/geosentinel/main.html). For all ill returning travelers seen at GeoSentinel sites from East Asia (N=4591), respiratory diseases accounted for 12.8% of all illness, morbidity second only to gastrointestinal infections in this population (unpublished data).
The World Health Organization as well as a number of national public health agencies have produced a series of sensible guidelines related to international travel that have now been proven highly efficacious in practice. Since the implementation, in late March, of the basic principles enunciated in the WHO document (reproduced following), chains of transmission of SARS have only been established in a single country, Taiwan. Hong Kong, Singapore, Vietnam and Canada were unlucky enough to have been blind-sided by the introduction of SARS virus into health care facilities and local communities in the days before the initial WHO worldwide alert was issued on March 12. Since then approximately 20 countries have imported small numbers of cases but have been able to rapidly isolate and contain those cases without secondary chains of transmission.
The point by point travel guidelines following should be read and promoted thoroughly by all travel medicine clinicians. Most travel medicine clinicians serve as resources within their community by businesses, academic institutions, government agencies and the travel industry. As to be expected with something as new and potentially frightening as SARS, some over-reaction by the public is inevitable. Although a large number of documents covering a myriad of travel-related situations for both travelers as well as hosting bodies have been produced, the essential underlying principles are quite few. These need to be clearly articulated by travel medicine practitioners in explaining resulting travel guidelines: the maximum incubation period for SARS is 10 days; asymptomatic individuals do not transmit SARS; almost all transmission is by direct respiratory droplets to those within a few feet, but in all affected areas there is documentation of a very small number of instances where there are environmental (hospital corridors, elevators, etc.) or other modes of transmission that are not yet well explained; there is no airborne transmission of SARS; most secondary cases have occurred in hospital settings and in household contacts not in travelers; no authoritative body advocates the use of surgical masks by the public while going about daily life; unlike most viral diseases, viral loads are low during the first week of symptoms precluding the ready development of highly sensitive early screening tests. The case definition will likely remain clinically based.
Flying is never a zero-risk proposition, rarely a crash occurs. Similarly the risk of SARS transmission on airliners is not zero but is very low. Only 4 flights have been associated with on-board transmission. These all occurred prior to the implementation of current pre-departure screening guidelines in late March. On 3 flights only 1 or 2 passengers or crew with direct contact with an index case were infected and on one of these flights a so-called super-spreader apparently infected 22 others.
The need for continued adherence to guidelines cannot be overstated. Airport temperature screening is likely a permanent part of the landscape and should be. As demonstrated in the Toronto second-wave in late April a single case missed in a medical care setting or at an international port of entry is enough to set up a community wide outbreak.