Skip directly to site content Skip directly to page options Skip directly to A-Z link Skip directly to A-Z link Skip directly to A-Z link
Volume 10, Number 7—July 2004
Conference Summary

Emerging Infections: What Have We Learned from SARS?

Alison P. Galvani*Comments to Author 
Author affiliation: *University of California, Berkeley, California, USA

Cite This Article

Given the current size and mobility of the human population, emerging diseases pose a continuing threat to global health. This threat became reality with the outbreak of severe acute respiratory syndrome (SARS). The emergence of a disease requires two steps: introduction into the human population and perpetuated transmission. Although preventing the introduction of a new disease is ideal, containing a zoonosis is a necessity. The lessons that we have learned from SARS were the topic of a meeting of The Royal Society on January 13, 2004, in London, England.

Zoonoses are responsible for most emerging infectious diseases, including infections caused by Ebola virus, West Nile virus, monkeypox, hantavirus, HIV, and new subtypes of influenza A. In the case of SARS coronavirus (SARS-CoV), serologic evidence indicates that the virus was spread through interspecies transmission from wild game markets in Guangdong, China (Malik Peiris, University of Hong Kong). This finding led to bans in the wild meat trade from Nan Shan Zhong (Guangzhou Respiratory Disease Research Institute) similar to the ban on eating nervous system tissue from cows that was implemented after new variant Creutzfeldt-Jakob disease emerged in Britain.

Ecologic changes, concomitant with increasing contact between humans and animal disease reservoirs, contribute to zoonoses. The emergence of SARS was facilitated by increased contact between people and animal disease reservoirs as the wild meat industry expanded recently. Global warming will likely contribute to the spread of dengue beyond tropical regions (Tony McMichael, National Centre for Epidemiology and Population Health, Canberra, Australia). Habitat fragmentation by deforestation may increase the contact between people and reservoir species. For example, hemorrhagic fever virus has been linked to deforestation in South America.

Containing an emerging disease depends on rapidly designing and implementing a control strategy appropriate to the epidemiology of the disease. Interdisciplinary and international collaboration occurred with unprecedented rapidity during the SARS outbreak. The network of laboratories in 17 countries organized by the World Health Organization (WHO) coordinated information sharing (David Heymann, WHO) and was instrumental in rapidly identifying the etiologic agent of SARS (1) and in fulfilling Koch’s postulates (2) (Albert Osterhaus, Erasmus University, Rotterdam).

As is typical of an emerging disease, no vaccines or drugs to combat SARS existed, making quarantine, patient isolation, travel restrictions, and contact precautions the only means of limiting transmission. Mathematic models provided a framework for evaluating alternative control measures and making predictions about the course of the epidemic (3,4). Previously, similar models had guided public health policy, for example, in halting an outbreak of hoof and mouth disease in the United Kingdom in 2001 (5,6). One of the complications in setting parameters in an emerging disease model is the difficulty in estimating epidemiologic limits from the initially small sample sizes. Thus, openly sharing data and analysis of key model parameters are vital.

The model must be appropriate to the nature of the disease and the accuracy of the parameter estimates (7). Stochasticity inherent in transmission dynamics will be particularly pronounced when infection prevalence is low. Population heterogeneity and the network structure of human interactions will affect the spread of an emerging disease. In the 2003 SARS outbreak, healthcare workers were at particular risk (8) and acted as bridges carrying the infection from the hospital and causing community wide epidemics. High-risk “core groups” have been a major focus of HIV/AIDS models for years (9), but the movement of SARS patients into the core (i.e., the hospital) adds a further complication (3).

The two waves of SARS clusters in Toronto (Robert Maunder, Mount Sinai Hospital, Toronto) highlight the need for surveillance even after an outbreak appears extinguished. Management of the SARS epidemic also demonstrated that public service infrastructure, which affords the greatest chance of success (3), is essential to the rapid containment of an outbreak. In areas most affected, contact tracing was important (10). In Guangdong, police departments tracked down contacts of infected persons, who were then followed up for 10 days after exposure. Evaluating the surge capacity of public health services and hospitals is one way to assess the preparedness of a medical system.

The case-fatality rate is a key determinant of the public health impact of an emerging disease and was high for SARS at approximately 15% (11). The relationship between infectiousness and onset of symptoms is also important. Patient isolation has greater potential as a control strategy if the illness can be diagnosed before the person becomes infectious (Roy Anderson, Imperial College London). In contrast, persons infected with influenza virus are highly infectious before they become symptomatic.

The rapidity of pathogen turnover means that evolution in pathogen populations can occur on a time scale that is epidemiologically relevant. Indeed, SARS-CoV evolved during the course of the SARS outbreak in China (12). Similarly, influenza is perpetuated in the human population by the evolution of new antigenic variants every year (Robin Bush, University of California, Irvine) (13). Even if the transmissibility of an emerging disease is initially below the threshold necessary to sustain it in a population, the potential for the organism’s evolution to higher levels may exist (14,15). Thus, one should not become complacent about diseases that are repeatedly introduced through zoonosis, but teeter on the edge of sustainability within the human population.

The success with which WHO coordinated the global collaboration in containing SARS galvanized the World Health Assembly to grant WHO greater authority to verify outbreaks, conduct investigations of outbreak severity, and evaluate the adequacy of control measures. The outcome of this new authority will depend on integrating the expertise of public health officials, medical doctors, and epidemiologists worldwide with guidance from disease transmission models. The SARS outbreak demonstrated that an epidemic in one part of the world is not just an individual nation’s problem but a global problem.



  1. Kuiken  T, Fouchier  RA, Schutten  M, Rimmelzwaan  GF, van Amerongen  G, van Riel, et al. Newly discovered coronavirus as the primary cause of severe acute respiratory syndrome. Lancet. 2003;362:26370. DOIPubMedGoogle Scholar
  2. Fouchier  RA, Kuiken  T, Schutten  M, van Amerogen  G, van Doornum  GJ, van Hoogen  BG, Aetiology: Koch’s postulates fulfilled for SARS virus. Nature. 2003;423:240. DOIPubMedGoogle Scholar
  3. Lloyd-Smith  JO, Galvani  AP, Getz  WM. Curtailing transmission of severe acute respiratory syndrome within a community and its hospital. Proc R Soc Lond B Biol Sci. 2003;270:197989. DOIPubMedGoogle Scholar
  4. Riley  S, Fraser  C, Donnelly  CA, Ghani  AC, Abu-Raddad  LJ, Hedley  AJ, Transmission dynamics of the etiological agent of severe acute respiratory syndrome (SARS) in Hong Kong: the impact of public health interventions. Science. 2003;300:19616. DOIPubMedGoogle Scholar
  5. Ferguson  NM, Donnelly  CA, Anderson  RM. Transmission intensity and impact of control policies on the foot and mouth epidemic in Great Britain. Nature. 2001;413:5428. DOIPubMedGoogle Scholar
  6. Keeling  MJ, Woolhouse  ME, Shaw  DJ, Matthews  L, Chase-Topping  M, Haydon  DT, Dynamics of the 2001 UK foot and mouth epidemic: stochastic dispersal in a heterogenous landscape. Science. 2001;294:8137. DOIPubMedGoogle Scholar
  7. May  RM. Uses and abuses of mathematics in biology. Science. 2004;303:7903. DOIPubMedGoogle Scholar
  8. Lee  N, Hui  D, Wu  A, Chan  P, Cameron  P, Joynt  GM, A major outbreak of severe acute respiratory syndrome in Hong Kong. N Engl J Med. 2003;348:198694. DOIPubMedGoogle Scholar
  9. Anderson  RM, May  RM. Infectious diseases of humans: dynamics and control. Oxford: Oxford University Press; 1990.
  10. Tsang  KW, Ho  PL, Ooi  GC, Yee  WK, Wang  T, Chan-Yeung  M, A cluster of cases of severe acute respiratory syndrome in Hong Kong. N Engl J Med. 2003;348:197785. DOIPubMedGoogle Scholar
  11. Galvani  AP, Lei  X, Jewell  NP. Severe acute respiratory syndrome: temporal stability and geographic variation in case-fatality rates and doubling times. Emerg Infect Dis. 2003;9:9914.PubMedGoogle Scholar
  12. Chinese SARS Molecular Epidemiology Consortium. Molecular evolution of the SARS coronavirus during the course of the SARS epidemic in China. Science. 2004;303:16669. Epub 2004 Jan 29. DOIPubMedGoogle Scholar
  13. Treanor  J. Influenza vaccine—outmaneuvering antigenic shift and drift. N Engl J Med. 2004;350:21820. DOIPubMedGoogle Scholar
  14. Antia  R, Regoes  RR, Koella  JC, Bergstrom  CT. The role of evolution in the emergence of infectious diseases. Nature. 2003;426:65861. DOIPubMedGoogle Scholar
  15. May  RM, Gupta  S, Mclean  AR. Infectious disease dynamics: what characterizes a successful invader? Philos Trans R Soc Lond B Biol Sci. 2001;356:90110. DOIPubMedGoogle Scholar


Cite This Article

DOI: 10.3201/eid1007.040166

Table of Contents – Volume 10, Number 7—July 2004

EID Search Options
presentation_01 Advanced Article Search – Search articles by author and/or keyword.
presentation_01 Articles by Country Search – Search articles by the topic country.
presentation_01 Article Type Search – Search articles by article type and issue.



Please use the form below to submit correspondence to the authors or contact them at the following address:

Alison P. Galvani; Department of Integrative Biology, University of California, Berkeley, CA 94720-3140, USA. fax: 410-643-6264

Send To

10000 character(s) remaining.


Page created: January 27, 2011
Page updated: January 27, 2011
Page reviewed: January 27, 2011
The conclusions, findings, and opinions expressed by authors contributing to this journal do not necessarily reflect the official position of the U.S. Department of Health and Human Services, the Public Health Service, the Centers for Disease Control and Prevention, or the authors' affiliated institutions. Use of trade names is for identification only and does not imply endorsement by any of the groups named above.