Can new infectious diseases be stopped? Lessons from SARS and avian influenza

Infectious diseases can emerge and spread with deadly and debilitating effects. But they can be stopped, as experience from SARS shows.

Severe acute respiratory syndrome (SARS) has often been described as the first serious new disease to emerge in the 21st century. As such, it fulfilled some of the prophecies made following another “first” for this century: the deliberate distribution, in an act of bioterrorism, of anthrax spores through the US postal system in late 2001.

That previously unthinkable event opened the eyes of politicians and the public to the damage that an infectious disease – whether of deliberate or natural origin – could cause in a highly mobile and closely interconnected world. It focused attention on several features of “modern” infectious diseases that make outbreaks, whatever their cause, an especially ominous threat. These include silent incubation periods that allow microbes to hide, unsuspected and undetected, in travellers, the speed of international spread made possible by the volume of air travel, and the potential for social and economic disruption amplified by electronic communications and the close interdependence of economies. Many scenarios were developed to predict the magnitude of illness and disruption following the deliberate spread of a disease, such as smallpox, having a long incubation period, a high fatality rate and no cure.

SARS had all of these features and more. Beginning in February 2003, it spread rapidly along the routes of worldwide air travel, placing any country with an international airport at risk. It had neither a vaccine nor an effective treatment, and killed upwards of one out of every ten persons it infected. It mimicked the symptoms of many other diseases, making diagnosis difficult, took its heaviest toll on healthcare staff, and spread most efficiently in hospitals. It also defied certain longstanding assumptions about the impact of epidemic-prone diseases in wealthy nations, and set an important test: can an emerging disease be stopped?

Events during the final decades of the 20th century had quickly eroded confidence that infectious diseases could be easily conquered. Beginning in the 1970s, the rapid development and spread of drug resistance rendered one antibiotic after another useless. Ebola haemorrhagic fever emerged in Africa in 1976, marking the most dramatic and potentially explosive epidemic of a new viral disease seen in the world for more than 30 years. In the early 1980s, AIDS struck, spread around the world, and rapidly became entrenched, eventually creating the greatest humanitarian crisis in history. Altogether, 40 new disease agents were detected during the last three decades.

Although the vulnerability of all nations to the infectious disease threat was widely accepted by the start of this century, many experts believed that new infectious diseases would not take hold with devastating effect in affluent nations. In these nations, the consequences of AIDS were greatly diminished by the advent of antiretroviral drugs and their wide availability.

Most other new diseases with high fatality, including the Ebola, Marburg, and Lassa haemorrhagic fevers, were considered diseases of poverty and poorly-equipped hospitals. Good sanitation and infection control, it was felt, would protect populations in the industrialised world from the devastation caused by epidemic-prone diseases in other parts of the world.

SARS proved otherwise. Good sanitation and high standards of healthcare were no protection. In fact, the spread of SARS was most efficient in sophisticated healthcare settings where certain medical procedures greatly increased the risk of transmission. SARS also showed how, in a closely interconnected and interdependent world, a deadly and poorly understood new disease can adversely affect economic growth, trade, tourism, business performance, political careers and social stability.

The public image of SARS was a white mask. The most vivid images of its economic impact were those of empty airports and strangely quiet city streets. SARS changed the way economists estimate disease-related economic losses. Previously, such estimates were based primarily on the costs of medical treatment, absenteeism from work and lost productivity. Efforts to calculate the full economic costs of SARS are ongoing, but range from US$30 billion to $100 billion, largely measured in terms of lost trade and foreign investment.

The consequences of SARS in affluent countries were devastating, but short-lived. The World Health Organization (WHO) first alerted the world to the new disease in mid-March 2003. From the outset, the objective was to seal off opportunities for its further spread, interrupt transmission, and prevent the new disease from becoming permanently established as yet another threat to global health. The experience with AIDS taught the world that the best response to a new disease is an all-out effort to prevent it from becoming established in the first place.

Fortunately, the international community was much better prepared for SARS than it was when Ebola or AIDS emerged. The response to SARS demonstrated some of the positive features of a globalised society: the advantages of rapid electronic communications and new information technologies for emergency response, and the willingness of the international community to form a united front against a common threat.

The possibility of stopping SARS “dead in its tracks” brought full support at levels ranging from heads of state to community volunteers, and in forms ranging from the electronic exchange of electron micrographs of the virus to mass distribution of thermometers. The willingness of the world’s best laboratory scientists, clinicians and epidemiologists to collaborate in around-the-clock “virtual” networks played a decisive role in generating knowledge and solving mysteries as the disease progressed.

Within a month, the causative agent – a new corona virus unlike any known before – had been identified. In less than four months following the first global alert, the WHO was able to announce, on 5 July 2003, that all known chains of human-to-human transmission had been broken. Ironically, the first new disease of the 21st century had been brought to bay using 19th century control tools – case detection, isolation, quarantine, infection control, and contact tracing – amplified by the latest communication technologies.

The possibility, opened by SARS, that emerging diseases might be stopped has given the roles of national and international surveillance for epidemic-prone diseases even greater importance. Surveillance systems for SARS are still on alert.

A new, though different, scare came in January 2004, when clinicians in Vietnam detected an unusual number of cases of severe respiratory illness, with high fatality and an unknown cause, at a hospital in Hanoi. The WHO was promptly informed, and its network of laboratories identified the cause as an especially deadly influenza virus that normally infects bird species exclusively. That finding caused Asian nations, and eventually the entire world, to increase their vigilance for cases of severe avian influenza in poultry and humans which could herald the start of another epidemic. It also encouraged governments to develop or strengthen pandemic preparedness plans and to find ways to use the unprecedented international collaboration seen during SARS to protect the world against other threats.

Future efforts to stop new diseases can draw three lessons from these experiences. First, good surveillance at both national and international levels is essential. Second, since infectious diseases potentially threaten every country, it is in every country’s best self-interest to collaborate internationally. Finally, international co-ordination – whether under the WHO’s leadership or the guidance of the International Health Regulations – is needed to ensure that our collective efforts bring the best results for international health.

©OECD Observer No 243, May 2004

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