WHO declared an end to the latest outbreak of severe acute respiratory syndrome (SARS) in China on May 18 despite lingering uncertainty about the means of infection at the country's top virology laboratory.
One woman died, eight people were infected, and hundreds of others were quarantined after two technicians at the National Institute of Virology in Beijing were mysteriously struck down with the disease last month.
But with no new cases in more than 3 weeks, WHO announced that the chain of human-to-human transmission had been broken before it could spread into the general population.
Although health officials were relieved to have avoided a repeat of last year's massive outbreak, which killed 774 people and infected 8000 people around the world, concerns remain about the safety breach at the institute.
WHO and the Chinese health ministry have launched investigations into the source of transmission, but they acknowledge that the results to date have been inconclusive.
Following similar outbreaks at research institutes in Taiwan and Singapore earlier this year, the most likely cause was initially suspected to be a laboratory accident involving live specimens of the SARS virus.
But no mishaps have been reported and the WHO team have yet to identify any procedural errors in the handling of samples. Adding to the mystery, the two infected researchers seem to have been struck down by the disease at different times and neither is believed to have come into contact with the live virus.
The first two patients have recovered, though the mother of one of them died after contracting SARS while caring for her child. Quarantine orders have been lifted on hundreds of other people who came into contact with the identified cases. According to the domestic media, 28 employees of the research lab are still under observation.
Despite the all clear, WHO expressed “serious concerns” about the handling of live SARS samples and reissued guidelines on correct safety procedure for laboratories around the world.
The Beijing institute ought to have been a model of caution as it is the main testing centre for SARS in China, the nation that was worst affected by last year's outbreak.
Under a plan that predates the latest outbreak, the institute is to be replaced by a new virology facility on which construction will begin in June.