Traces of Radiation from Japan?

So I read this CNN news this morning about slightly higher radiation levels that could possibly come from Japan.

But, on a portion of its website dedicated to tracking such radiation, the Environmental Protection Agency noted Wednesday that these and other readings "show typical fluctuation in background radiation levels" and -- thus far -- "are far below levels of concern."

Sampling from a monitor in Colorado -- part of a national network of stations on the lookout for radioactivity -- detected miniscule amounts of iodine-131, a radioactive form of iodine, the state's public health and environmental department said Wednesday in a press release.

On the same day in Portland, Oregon, tiny quantities of iodine-131 were also detected by an Environmental Protection Agency air monitor, Oregon public health officials said.

Now, the physicist in me started asking "It's one thing to detect slightly higher-than-normal radiation, it is another to actually know the source of such radiation." How can one verify a statement that says ".. trace amounts of radioactive particles that have likely drifted about 5,000 miles from a quake and tsunami-damaged nuclear power plant in Japan.. " Is the detection of such iodine isotopes rather uncommon, so much so that their detection now can be plausibly linked to the nuclear accident in Japan? Can someone who is an expert in this field clarify this?

Zz.