World Health Organisation experts yesterday took environmental samples from Amoy Gardens for laboratory tests as they began an investigation into the government's findings over the Sars outbreak at the Kowloon Bay estate that killed 27 residents. The team spent about three hours visiting three units and sampling material on wall surfaces, ventilation systems and pipes in Block E for further testing. No samples were taken from recovered patients living on the estate. Virologist and team leader Heinz Feldmann said they chose to open their investigation by revisiting the theory proposed by the government. The government investigation blamed a faulty sewerage system and the so-called chimney effect - which allowed contaminated droplets to travel up the light-well - as the cause of the outbreak that infected more than 300 residents in the estate. The WHO team re-sampled material at places that had been examined by government investigators. 'We are following several hypotheses that have been developed from local scientists and the government,' Dr Feldmann said. 'Once you set up some ideas, theories and hypotheses, you will always come up with more things to do to support it. We felt this was the right way to go at this point.' Dr Feldmann said they believed that the outbreak at Amoy Gardens was more likely to have been caused by a combination of factors. 'As the virus was distributed to the sewerage system and supported by ventilation or a chimney effect [at Amoy Gardens], we would still be able to find the footprint of the virus, not the live virus, but its genetic materials on some surfaces,' he said. Yesterday morning, the team also met engineering experts from the Hong Kong University who have set up a model to study the chimney effect and sewerage system fault identified at Block E. The team might revisit Amoy Gardens and will inspect Kowloon's Metropole Hotel, Koway Court in Chai Wan and Hing Tung House in Wong Tai Sin - all sites of Sars infections. Coinciding with the visit of the WHO team, Amoy Gardens residents took part in a Buddhist cleansing ceremony.