SARS, in contrast to diseases like flu or rubella, is only moderately transmissible. The number of secondary SARS cases per index case, ranging in one epidemiologic study from 2.2 to 3.6, are considerably lower than those estimated for most other diseases with respiratory transmission (Lipsitch). This indicates that a combination of control measures, including shortening the time from symptom onset to isolation of patients, effective contact tracing and quarantine of exposed persons, can be effective in containing SARS. Indeed, such measures have been successful and have contributed to the prevention of major outbreaks in other countries. On the other hand, in the absence of such effective measures, SARS has the potential to spread widely (Lipsitch).

In the absence of a vaccine, the most effective way to control a new viral disease such as SARS is to break the chain of transmission from infected to healthy persons. In almost all documented cases, SARS is spread through close face-to-face contact with infected droplets when a patient sneezes or coughs (WHO, WER 20/2003).

For SARS, three activities - case detection, patient isolation and contact tracing - can reduce the number of people exposed to each infectious case and eventually break the chain of transmission (WHO, WER 20/2003):

1. Case detection aims to identify SARS cases as soon after the onset of illness as possible.
2. Once cases are identified, the next step is to ensure their prompt isolation in a properly equipped facility, and management according to strict infection control procedures.
3. The third activity - the detective work - involves the identification of all close contacts of each case and assurance of their careful follow-up, including daily health checks and possible voluntary home isolation.

Together, these activities limit the daily number of contacts possible for each potentially infectious case. They also work to shorten the amount of time that lapses between the onset of illness and isolation of the patient, thus reducing the opportunities for the virus to spread to other patients (WHO WER 20/2003).

The World Health Organization (WHO) played a vital role in the containment of the first global outbreak of SARS.

After issuing a global alert about cases of severe atypical pneumonia following reports of cases among staff in the Hanoi and Hong Kong hospitals on March 12, the WHO received additional reports of more cases. Three days later, the WHO issued emergency travel recommendations to alert health authorities, physicians, and the traveling public to what was now perceived to be a worldwide threat to health. The alert included the first WHO emergency travel advisory to international travelers, healthcare professionals and health authorities, advising all individuals traveling to affected areas to be watchful for the development of symptoms for a period of 10 days after returning (http://www.who.int/csr/sarsarchive/2003_03_ 15/en/).

The decision was based on five different but related factors (WHO, Status of the Outbreak):

1. The causative agent, and therefore the potential for continued spread, of this new disease were not yet known.
2. The outbreaks appeared to pose a great risk to health workers who managed patients, and to the family members and other close contacts of patients.
3. Many different antibiotics and antiviral therapies had been tried empirically and did not seem to have an effect.
4. Though the numbers were initially small, a significant percentage of patients (25 of 26 hospital staff in Hanoi, and 24 of 39 hospital staff in Hong Kong) had rapidly progressed to respiratory failure, requiring intensive care and causing some deaths in previously healthy persons.
5. The disease had moved out of its initial focus in Asia and appeared to have spread to North America and Europe.

Within less than two weeks, a collaborative network of laboratories set up by the WHO identified a novel coronavirus as the probable etiologic agent of SARS (see Chapter 2: Virology).

Early in April, travel advisories became more specific. On April 2, the WHO recommended that persons traveling to Hong Kong and the Guangdong Province of China consider postponing all but essential travel. (http://www.who.int/csr/sarsarchive/2003_04_ 02/en/). On April 23, the WHO extended its travel advice to Beijing and the Shanxi Province in China and to Toronto, Canada, http://www.who.int/csr/sarsarchive/2003_04_ 23/en/, and on May 8 to Tianjin, Inner Mongolia, and Taipei in Taiwan (WHO Update 50).

The global alert and the global effort coordinated by the WHO achieved its purpose. All countries with imported cases, with the exception of provinces in China, were able through

1. prompt detection of cases
2. immediate isolation, strict infection control, and
3. vigorous contact tracing

to either prevent further transmission or to keep the number of additional cases very low. The early management of the SARS epidemic may well serve as a model for the containment of future epidemics and pandemics.

At the beginning of July, all travel restrictions were lifted (WHO Update 96).

The most important message for international travelers concerning SARS is to be aware of the main symptoms of SARS: high fever (> 38° C or 100.4° F), dry cough, shortness of breath or breathing difficulties. Persons who experience these symptoms and who have been in an area where there has been recent local transmission of SARS in the last 10 days are advised to contact a doctor (WHO WER 14/2003).

To further reduce the risk that travelers may carry the SARS virus to new areas, international travelers departing from areas with local transmission in the B or C categories (see "Areas with recent local transmission", http://www.who.int/csr/sarsareas/en/) should be screened for possible SARS at the time of departure. Such screening involves answering two or three questions and may include a temperature check. Travelers with one or more symptoms of SARS and who have a history of exposure, or who have fever, or who appear acutely ill should be assessed by a healthcare worker and may be advised to postpone their trip until they have recovered.

See also "Recommended procedures for prevention and management of probable cases of SARS on International Cruise Vessels", http://www.who.int/csr/sars/travel/vessels/en/ .

The primary focus of SARS surveillance activities in countries without or with very few SARS cases is on the early identification and isolation of patients who have suspected SARS.

In contrast, countries which are affected by a severe SARS outbreak must immediately take a variety of sometimes unpopular measures to contain the epidemic. These measures generally include

1. the creation of an emergency operating center
2. the designation of one or more SARS hospitals
3. the institution of efficient quarantine measures, possibly based on an extended case definition (see below)
4. the rapid approval of pending legislation

In Singapore, the Tan Tock Seng Hospital, which is the second largest hospital in town (1500 beds) and site of the initial outbreak, was closed and designated to be the SARS hospital. Schools were closed and all public events postponed indefinitely (Mukherjee). Singapore used its military forces to assist in contact tracing and enforcement of home quarantine. All persons who were household, social, hospital, and occupational contacts during the 10 days before the onset of symptoms were traced to identify the source of infection. Persons identified as having had contact with a SARS patient from the onset of symptoms to the date of isolation were placed in home quarantine (WHO Update 70). Other measures included screening passengers at the airport and seaports, imposing a no-visitors rule on all public hospitals, and use of a dedicated private ambulance service to transport all possible cases to the SARS-designated hospital (WHO Update 70). Military forces were deployed to assist in contact tracing and to enforce quarantines. No visitors were allowed into any public hospital.

In Taiwan, the Department of Health efforts focused on limiting nosocomial transmission by designating dedicated SARS hospitals throughout the island. Approximately 100 "fever clinics" were also established to identify potential SARS patients and to minimize the risk of transmission in emergency departments. Patient care capacity was expanded by the construction of 1,000 additional negative pressure isolation rooms. Campsites and military facilities were identified to accommodate quarantined residents, and home quarantine was to be enforced through web-based cameras (MMWR 52; 461-6).

On April 24, in Singapore, the Infectious Disease Act was amended with penalties for violations 1) to require persons who might have an infectious disease to go to a designated treatment center and to prohibit them from going to public places; 2) to prohibit breaking home quarantine with the possibility of electronic tagging and forced detention for violators; and 3) to permit contaminated areas to be quarantined and any suspected sources of infection to be destroyed. In addition, persons throughout the country were requested to monitor body temperature and to stay home or seek medical care if any signs or symptoms suggestive of SARS appeared (MMWR 52: 405-11).

This legislation allowed mandatory home quarantine for 10 days, which was enforced by CISCO, a Singapore Security Agency. CISCO served the quarantine order and installed an electronic picture (ePIC) camera in the home of each contact (MMWR 52: 405-11).

The penalty for violating quarantine was raised to as much as $5,800 and six months in prison.

Prevention aims at identifying and isolating all people suspected of being infected with the SARS virus. The main criteria in the current WHO case definition for suspected SARS are fever (> 38°C) and respiratory symptoms such as cough, shortness of breath, or breathing difficulty, and a history of exposure (see Chapter below "Case Definition"). This definition might not be wide enough when facing an outbreak.

In one study, in the early stages of SARS, the main discriminating symptoms were not cough and breathing difficulty but fever, chills, malaise, myalgia, rigors, and, possibly, abdominal pain and headache also occurred (Rainer). Documented fever (> 38°C) was uncommon in the early stages, and radiological evidence of pneumonic changes often preceded the fever. The authors calculated that the WHO case definition has a sensitivity of 26% and a negative predictive value of 85%. The case definition, which was initially based on patients who were already hospitalized, might therefore define the tip of the iceberg of an epidemic, and not be sufficiently sensitive in assessing patients before admission to hospital (Rainer).

In addition, patients presenting with overt symptoms suggestive of SARS, including fever, are unlikely to be the source of an outbreak; in contrast, unidentified SARS cases have, to date, been responsible for most of the sudden outbreaks. Several factors contribute to the difficulties in recognizing cases of SARS (MMWR 52; 461-6):

• Early symptoms are non-specific and may be associated with other more common illnesses
• Patients with SARS who are immunocompromised or who have chronic conditions (e.g., diabetes mellitus or chronic renal insufficiency) might not have fever when acutely ill or have symptoms attributable to underlying disease, delaying the diagnosis of SARS
• Some patients might not reveal useful contact information (e.g., exposure to an implicated healthcare facility) for fear of being stigmatized by the local community or causing their friends and families to be quarantined

These cases do not arise suspicion, are not isolated or managed according to strict procedures of infection control, have no restrictions on visitors, and are frequently transferred to other hospitals for further treatment or tests (WHO Update 83).

In order to prevent transmission from asymptomatic or mildly symptomatic and/or unrecognized patients, a "wide net" approach has been proposed by some national authorities.

Singapore changed the threshold criteria for initial isolation, picking up virtually every person with symptoms that might possibly indicate SARS for investigation and monitoring, regardless of whether the person had been in contact with a SARS patient (WHO Update 70). The "wide net" included all individuals with a low grade fever, chest radiograph abnormalities, or respiratory symptoms alone, leading to the admission to newly created "fever wards" of any patient with fever or respiratory symptoms or a chest x-ray abnormality which could not otherwise be explained. The rationale behind this approach is that a patient’s likelihood of having SARS becomes clearer after 48 hours of monitoring respiratory symptoms, temperature, white cell count (for lymphopenia) and chest x-rays (Fisher).

In one hospital in Singapore, this policy led within three weeks to the admission to isolation wards of 275 individuals who did not meet the WHO criteria. 72 individuals were later referred to the SARS hospital. No secondary infections were caused (Fisher).

Unfortunately, tests to identify SARS patients at the earliest stages of disease are not expected to be widely available soon. Early introduction of quarantine procedures for SARS should therefore be considered by health authorities. Isolation and quarantine procedures will be less effective as more cases accrue. Therefore, stringent measures implemented early in the course of the epidemic prevent the need for stricter measures as the epidemic spreads (Lipsitch).

During March, health officials in Singapore, Hong Kong, and Canada implemented quarantine and isolation measures to limit the spread of SARS. In Singapore, all primary contacts of these individuals were placed on home quarantine with financial penalties for violation; they were required to appear regularly before web cameras installed in their homes and to wear electronic bracelets if they failed to do so (Mukherjee).

On April 4, 2003, SARS was added to the list of quarantinable communicable diseases in the US. A presidential act provided the CDC with the legal authority to implement isolation and quarantine measures as part of transmissible disease-control measures, if necessary.

Quarantine does not always mean being confined to a hospital or military camp. If patients are not sick enough to warrant admission, the community may be best served by sending such patients home, provided patients can restrict their activities in a responsible manner until they are asymptomatic (Masur).

SARS Co-V may be transmitted in quarantine communities. There has been at least one report about SARS Co-V transmission during quarantine (WHO WER 22/2003). Putting patients with suspected or probable SARS and convalescent cases into isolation cubicles, each accommodating four to six patients (So), is therefore not the appropriate procedure to avoid infection. Don't "cohort" suspected cases! Patients diagnosed with SARS may or may not have the SARS virus, but they are at risk of contracting the infection if they are grouped with infected patients (Hon 2003b).