WHO said there are indications of success with its efforts to seal off opportunities for SARS to spread both within countries and internationally. For example, during a videoconference with Singaporean officials yesterday, the agency learned that 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 by last week, thus reducing by half the amount of time infected persons can expose others to the SARS virus.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, WHO stressed. Singapore has instituted such comprehensive procedures for identifying cases and isolation, and these measures appear to be working, the agency said.”If each new SARS patient infects more than one additional person, then the number of new cases will increase with time. If each new SARS patient infects one further person, then the number of new cases will remain static,” WHO stated. “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 die out.”WHO said breaking the chain of transmission entails identifying SARS cases soon after onset of illness, ensuring prompt isolation of cases in a properly equipped facility and the tracing of all close contacts of each case for careful monitoring. Together, these activities can reduce the number of people exposed to each infectious case.Despite this indication that the epidemic is coming under control, the Coordinator of WHO’s Global Alert and Response Programme, Michael Ryan, warned against becoming complacent, stressing that this is the time to intensify prevention efforts.As of today, a cumulative total of 7,548 probable SARS cases, with 573 deaths, have been reported from 29 countries.