Health experts are worried that a new, more virulent strain may be to blame.

卫生专家担心这一现象归咎于一种毒力更强的新菌种。

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It remains to be seen whether the virus will mutate into a more virulent strain.

该病毒是否会产生变异，成为毒性更强的病毒株，仍有等观察。

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Half of the victims have been hospitalised, a high rate that may indicate an especially virulent strain of E. coli.

半数受害者都已住院，如此高的住院率表明这可能是一种毒性特别强的大肠杆菌菌株。

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It's a virulent strain that occurs when a person with TB fails to complete the six to nine-month course of medication or catches TB from another person who is ill with a drug resistant-strain.

VOA: standard.2010.07.12

No target is too mighty, or too obscure, for this new and virulent strain of oratory.

FORBES: Attack of the Blogs

Half of the victims have been hospitalised, a high rate that may indicate an especially virulent strain of E. coli.

ECONOMIST: Those healthy green leaves cause a terrible scare

They then subdivided the groups and infected the resulting subgroups with either H3N1, a mild strain of influenza, or H1N1, a virulent strain.

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