英文解釈
下記の英文の"a rarity "以下がわかりません（文の切れ目、意味など）。 わかる方がいらっしゃいましたら教えてください。
That's still true in many parts of the United States. But in some places, life expectancy has leveled off or even dropped slightly - a rarity in a developed country and, public health officials say, a cause for alarm.
■補足
【前後の文】
A baby born in America in 2009 could expect to live an average of 78 years, according to estimates from the U.S. Centers for Disease Control (CDC).
That's still true in many parts of the United States. But in some places, life expectancy has leveled off or even dropped slightly - a rarity in a developed country and, public health officials say, a cause for alarm. A study in the Journal of Health Metrics shows the United States now ranks behind 10 other developed countries when it comes to life expectancy, even though Americans spend more on health care than people in most other countries.
【出展】
VOA：http://www.voanews.com/english/news/health/Life-Expectancy-Declining-In-Large-Parts-of-US-124128694.html
