Infectious Diseases: January 31, 2005

John Bartlett, MD


February 16, 2005

In This Article

SARS and Public Health Interventions

Bell DM. Public health interventions and SARS spread, 2003. Emerg Infect Dis. 2004;10:1900-1906 . The World Health Organization (WHO) Working Group on Prevention of International and Community Transmission of severe acute respiratory syndrome (SARS) reviewed the experience with strategies to prevent the transmission of SARS during the 2003 epidemic. Some of the idiosyncrasies of this epidemic are important to acknowledge in the context of effectiveness of prevention methods:

  • Transmission was primarily through respiratory droplets with some environmental spread. There was minimal airborne spread. Some important exceptions to this pattern were Hotel M and Amoy Gardens, both in Hong Kong, China.

  • Transmission occurred primarily in healthcare settings and household settings due to "person-to-person contact."

  • Children were infrequently infected and did not appear to be important in transmission.

  • Transmission did not occur prior to the onset of symptoms and was infrequent at the onset of illness; the peak time of transmission was week 2 of illness in association with maximum respiratory symptoms, usually during hospitalization.

  • The incubation time was relatively long with a median of 4-5 days and this facilitated contact tracing.

  • The average number of new cases from a single infection was 2-4, although there were a small number of "superspreaders" who usually transmitted in hospitals or households before infection-control precautions were in place.

The following measures were reviewed:

  1. Identifying patients and quarantining contacts: These were judged "highly effective in preventing transmission" according to studies in Singapore.[1] Quarantine was usually at home or in a designated residential facility for travelers, persons who did not wish to expose families, homeless persons, and noncompliant persons. It was noted that quarantine, as historically used, would be unacceptable at the current time. This is most acceptable and most effective when given in the context of protecting the health and rights of the quarantined persons. Exposed persons must be separated from symptomatic persons, should be quarantined for the maximum incubation period, and should be given treatment at the first sign of illness. In several countries, the quarantine was legally mandated and monitored by neighborhood support groups, police, other workers, or video cameras in homes. The frequency of SARS in quarantined persons was variable: China-Taiwan, .2%; Hong Kong, 2.7%; and Beijing, 3.8% to 6.3%

  2. Methods to improve isolation and case detection: These efforts included requests of entire populations to measure the temperature at least once daily, the establishment of fever telephone hotlines, and fever-evaluation clinics. Thermal scanning was commonly done in public places where transmission was suspected, but data on its effectiveness are not available except for Beijing, where thermal screening was proven to be ineffective.[2]

  3. Methods to increase "social distance": This includes canceling of mass gatherings, such as schools, public facilities, and theaters. It also includes some requirements for the wearing of masks. An evaluation of these methods is difficult because they were often accompanied by other measures, such as enhanced contact tracing, enhanced hand washing, or increased environmental disinfection. One study appeared to support the use of masks in public.[3]

  4. Disinfection: There is little evidence for effectiveness.

  5. Travel advisories: There are no adequate studies to evaluate.

  6. Health alerts to entering travelers: There are no adequate studies with follow-up to determine the impact of alerting approximately 1.8 million travelers arriving from affected areas.

  7. International travel-entry screening: A global survey indicates that 72 patients with imported probable or confirmed SARS included 30 (42%) who had the onset of symptoms before the day of entry and 42 (58%) who had symptoms develop after entry:

    • Analysis of health declarations by entering travelers at international borders in Canada, mainland China, Hong Kong, Taiwan, and Singapore showed that a total of 45.4 million travelers completed declarations; about 13,000 reported symptoms suggesting SARS; and 4 subsequently proved to have SARS.

    • Temperature screening of 13,839,500 travelers entering or leaving Beijing by air, train, or car showed that 5097 had fever and 12 had probable SARS.[4] In Taiwan, travelers from affected areas were quarantined, and this led to the identification of probable or suspected SARS in 21 (.03%) of 80,813; none of these 21 patients were detected by thermal scanning.

  8. International travelers: exit screening: Screening at exit from countries with SARS was recommended by WHO; data were available for the 2.4 million travelers who completed this declaration and for the 7.9 million who were thermally scanned. There were 2 cases of SARS detected by health declaration and none by thermal scanning.

  9. Thermal scanning of entering travelers at international borders: Data for 35.7 million passengers from Canada, mainland China, Hong Kong, Taiwan, and Singapore indicated that 10,729 were febrile by scan and 4177 had fever confirmed orally; none of these patients were found to have SARS.

  10. Transmission on commercial aircraft: Five international flights were associated with the transmission of SARS from patients to passengers and crew. The most extensively studied was a flight in which secondary cases were detected in 22 of 120 (18%) of passengers.[5] In this report, the highest risk was in patients seated closest to the index case, but more patients were seated at some distance. Other studies have found no transmission to patients who were exposed to a SARS patient on multiple flights.[6]

On the basis of these observations, the following conclusions were made: SARS was largely contained by traditional public health strategies, including case detection and isolation, quarantine of close contacts, and enhanced infection control. The effectiveness of increasing social distance and wearing of masks is not clear. There was minimal benefit of screening travelers. These lessons will be useful in the event of another epidemic of SARS. The real question concerns avian influenza: The study authors conclude that the lessons from SARS would be particularly useful if applied to avian flu, if the strain is not fully adapted to human-to-human transmission; for a pandemic strain, these experiences would not halt transmission but may "buy time" to permit other interventions, such as drugs and vaccines.


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