ABSTRACT - World Health Orgn is relying on time-tested rule of thumb used by epidemiologists in declaring Vietnam first country to stop its outbreak of SARS; rule says epidemic is over if no new cases occur in time span that is double longest known incubation period of the disease; SARS has 10-day incubation period and no new cases have been detected in Vietnam in 20 days; Vietnam had total of 63 cases and 5 deaths; WHO spokesman gives credit for Vietnam's success to old-fashioned infection-control measures; says there was high level of political commitment there from beginning (M) In declaring Vietnam the first country to stop its outbreak of severe acute respiratory syndrome, or SARS, the World Health Organization relied on a time-tested rule of thumb used by epidemiologists.

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