加州卫生服务部的埃里·卡维斯硕士研究员，表示面向公众的健康宣传活动和媒体报道的可能是上述概率下降原因。

Researcher Erica Weis, MPH, of California's health services department, suggests that public health campaigns and media coverage of outbreaks may be responsible for the decline.

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乔治梅森大学墨卡托斯中心的自由市场经济学家维罗妮克·德鲁吉表示：“这非常令人费解。”

"It's very puzzling," says free market economist Veronique de Rugy of the Mercatus Center at George Mason University.

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乔治梅森大学墨卡托斯中心的自由市场经济学家维罗妮克·德鲁吉表示：“这非常令人费解。”

"It's very puzzling," says free-market economist Veronique de Rugy of the Mercatus Center at George Mason University.

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