No further potential source of exposure was identified.

未查明进一步潜在接触源。

youdao

This is the first, and, thus far, the only, indication of a possible source of exposure.

这是第一次，也是迄今唯一的一次出现可能接触源的迹象。

youdao

Investigation of the July family cluster was unable to determine the source of exposure.

对7月家庭群集的调查未能确定接触源。

youdao

These bills will curb lead levels in water pipes, a major source of harmful lead exposure for children, and help address diesel engine pollution that is linked to serious health conditions like asthma and heart and lung disease.

WHITEHOUSE: Council on Environmental Quality Blog

The WHO said investigations were being conducted into the likely source of the infection, the method of exposure, and the possibility of human-to-human transmission of the virus.

FORBES: Is a New SARS-like Virus Spreading in the Middle East?

The best source of vitamin D is the sun, but because sunlight cases cancer, people are advised to limit sun exposure.

WSJ: Vitamin D and Calcium Supplements May Not Stop Fractures