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Severe acute respiratory syndrome
  1. G Rezza
  1. Istituto Superiore di Sanità, Rome, Italy
  1. Correspondence to:
 Dr G Rezza; 
 g.rezza{at}iss.it

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A challenge for public health

In this issue of the journal, Lee and Abdullah focus on the adoption of hygienic and health promotion measures in Hong Kong for controlling the spread of severe acute respiratory syndrome (SARS).1 One of the interesting aspects of this work is that it provides an insider’s point of view, yet these hygienic measures need to be discussed in the overall context of the outbreak, including the other public health interventions that have been performed in both Hong Kong and other heavily affected cities.

It should first be mentioned that one of the distinguishing characteristics of SARS is that for the first time in many years the entire world has perceived an outbreak as a life threatening event with a great non-discriminatory potential for diffusion, whereas this has not been the case for other epidemics of emerging infections in the era of antibiotics. For example, despite the fact that the outbreaks of Ebola and Lassa fever produced high case fatality rates in Sub-Saharan Africa, they remained for the most part confined to remote areas and were thus never truly perceived as global level threats by persons living in industrialised countries. Although the HIV/AIDS pandemic represents a true global level disaster, knowledge of the selective modalities of transmission has led to its being often perceived as affecting only marginalised people in wealthy countries and people living in poor resource countries.

The global level concern surrounding SARS began to take form when reports from Hong Kong and China’s Guandong province incited the WHO to launch a global alert, unprecedented in its history, that recommended the postponement of all but essential travel to the affected areas and the screening of airline passengers2; around the same time, the public health measures for reducing the risk of transmission in the affected areas became extremely strict. None the less, it is fair to say that we were not prepared to cope with the SARS emergency, for several reasons. Specifically, SARS, which is caused by a new human coronavirus (referred to as “SARS-CoV”), is mainly transmitted through respiratory secretions, and these types of infections are not as easily controlled as those transmitted through, for example, sexual intercourse or blood. Secondly, that the infection is viral makes treatment difficult, given the scarcity of effective antiviral drugs in general. Thirdly, there is not much experience with vaccines against other known human coronaviruses (229E and OC43-like), as they have only been associated with mild pathogens, which cause about 30% of seasonal common colds.

However, despite these hurdles, the epidemic curves of SARS in Guandong, Hong Kong, Singapore, Beijing, Toronto, and Taiwan all showed a rather rapid decline after the implementation of stringent public health measures,3 and in Hanoi, where WHO officer Carlo Urbani recommended that stringent measures be adopted immediately after he identified the disease, the outbreak was contained within a few weeks. The group of Roy Anderson of Imperial College in London has emphasised that the spread of infection has been successfully limited because mixing and travel were restricted through measures that the authors defined as “draconian”, including: the isolation of cases, contact tracing and mandatory home quarantine, suspension of school sessions, health declarations for visitors, isolation of residents of a building and their subsequent move to rural isolation camps, and body temperature checks for air passengers.4 Although the application and enforcement of these measures varied across the different affected areas, it can be safely be said that they were effective.

Insight into the reasons for this success has been provided by the dynamic mathematical models designed to determine how and why the disease had spread among populations in Asia and elsewhere. According to preliminary analyses of the outbreak in Hong Kong, SARS-CoV is more likely to be transmitted by direct contact or by larger virus laden droplets, which travel only one or two metres, as compared with lighter airborne particles or aerosols, as is the case for influenza and measles.5,6 This theory is supported by the comparatively low basic case reproduction number (R0) (that is, the average number of persons infected by each case at the beginning of the epidemic), which seems to range from 2 to 4, with the exception of two super-spread events; the theory is also supported by the occurrence of clusters of cases linked to symptomatic people in a particular spatial setting (for example, healthcare facilities or households).

This success, which to some extent was unexpected, has played down the criticism concerning the supposed non-effectiveness of the cordone sanitaire in the era of globalisation. However, whether or not imposing these measures represents an unacceptable infringement of individual rights continues to be a matter of debate.

A challenge for public health

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