In the past, explanations have concentrated on environmental factors such as the smoking habits of the parents, bacterial infection and (most famously) a baby's sleeping position.

过去人们将病因归咎于环境因素，如父母的抽烟习惯，细菌感染以及婴儿的胎位(这是最为著名的说法)。

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Investigations into the source of his infection indicate similar environmental exposure as his mother.

对其感染源的调查表明与其母亲相似的环境接触。

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The cases may have acquired their infection from a shared environmental exposure yet to be identified.

这些病例可能从尚未查明的共同环境接触中获得感染。

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It is based on research carried out by Glasgow University's Centre for Drug Misuse Research in conjunction with the Scottish Centre for Infection and Environmental Health.

BBC: Large-scale drugs problem revealed

Information about any unusual infection in a drug user should be given to the local public health consultant who should inform the Scottish Centre for Infection and Environmental Health.

BBC: Killer heroin report published

This experiment does, however, suggest that genetics alone may explain some cases of SIDS. In the past, explanations have concentrated on environmental factors such as the smoking habits of the parents, bacterial infection and (most famously) a baby's sleeping position.

ECONOMIST: Sudden infant death syndrome