Officials suspect a type of chemical exposure is to blame, but the cause of the illness has not yet been verified. Symptoms include coughing, shortness of breath, fatigue, vomiting and diarrhea. All of the cases are linked to vaping or e-cigarette use. Some affected people used e-cigarette products with THC, while others used nicotine ones or those with both THC and nicotine. Some people used black market products.

The agency isn't targeting individuals for their personal use of controlled substances through the investigation, according to Mitch Zeller, the director of FDA's Center for Tobacco Products. The probe extends across several states, hundreds of cases and a broad range of products and substances, Anne Schuchat, the CDC's principal deputy director, told reporters on a conference call.

News of the investigation comes amid a regulatory crackdown on vaping and e-cigarettes in the US and elsewhere. The federal government plans to ban non-tobacco-flavored e-cigs while New York and Michigan have already blocked sales of them. Chinese retailers stopped sales of Juul products this week, while India has effectively banned e-cigarettes.