UN Chronicle | The Global Response to SARS

The Global Response to SARS
By Erika Reinhardt, for the Chronicle

Article

The global approach to SARS, coordinated by the World Health Organization, has been aimed at sealing off opportunities for further spread, both within countries reporting cases and internationally. Experiences in a growing number of countries indicate that the disease can be contained, thus supporting the WHO overall objective: to prevent SARS from becoming widely established as another new disease in humans.

In the absence of a vaccine, the most effective way to control a new 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. Three activities-case detection, patient isolation, and contact tracing-can reduce the number of people exposed to each infectious case of SARS and eventually break the chain of transmission.

Detection aims to identify SARS cases as soon after onset of illness as possible and once identified, the next step is to ensure their prompt isolation in a properly equipped facility and management according to strict procedures of infection control. Tracing-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 onset of the illness and isolation of the patient, thus reducing opportunities for the virus to spread to others. The effectiveness of these measures is reflected in an important indicator of disease transmission-the so-called "effective reproduction number".

This is the average number of new cases generated by each case. If each new SARS patient infects more than one person, then the number of new cases will increase with time. If each new SARS patient infects only one further person, then the number of new cases will remain static. However, if each new SARS patient infects on average less than one further person, then the number of new cases will fall and the outbreak will eventually die out.

Containing the epidemic remains a WHO priority, both in its support to individual countries and globally. Singapore has instituted comprehensive procedures for contact tracing and isolation, and these measures appear to be working. The so-called "time to isolation" had been reduced from a high of three days in the early phase of the outbreak to 1.4 days, thus reducing by half the amount of time infected persons can expose others to the SARS virus. These measures are being applied elsewhere, with outbreaks coming under control in several areas.

WHO is now collecting the data needed to systematically assess the effectiveness of these and other control measures being implemented worldwide and will strengthen its recommendations accordingly. Nonetheless, as SARS has clearly demonstrated, a single case admitted to an unprepared hospital can ignite a new outbreak. While trends are moving in an encouraging direction in many areas, even greater focus on control measures is needed if SARS is to be contained globally. WHO experiences with outbreaks of Ebola haemorrhagic fever have repeatedly shown that the initial stages of containment are the most dangerous time to start lowering the level of control. "We cannot become complacent", says Michael J. Ryan, Coordinator of the WHO Global Alert and Response Programme. "In fact, this is the time to intensify our efforts."

Point of fact: Fatality. The likelihood of dying from SARS has been shown to depend on the profile of the cases, including the age group most affected and the presence of underlying disease, with an overall case fatality estimate of 14% to 15%. WHO estimates the case fatality ratio to be less than 1% in persons under 24 years, 6% in persons aged 25 to 44 years, 15% in persons aged 45 to 64 years, and greater than 50% in persons over 65 years.

Point of fact: Incubation. The incubation period, which is the time from exposure to a causative agent to onset of disease, is particularly important as it forms the basis for many recommended control measures, including contact tracing and the duration of home isolation for contacts of probable SARS cases. Knowledge about the incubation period can also help physicians make diagnostic decisions about whether the presenting symptoms and clinical history of a patient point to SARS or to some other disease. WHO continues to conclude that the current best estimate of the maximum incubation period is 10 days.

Point of fact: Isolation. A short time between onset of symptoms and isolation reduces opportunities for transmission to others. It also reduces the number of contacts requiring active follow-up, and thus relieves some of the burden on health services. Prompt hospitalization gives patients the best chance of receiving possibly life-saving care should their condition take a critical course. WHO continues to recommend the earliest possible isolation of all suspect and probable cases of SARS.

Go Back Top