Health authorities say the number of people dying from diseases related to the use of e-cigarettes in the United States has increased to at least 19, while more than 1,000 people have suffered from lung damage that may be related to smoking.
Officials have not yet identified the cause of the outbreak, which can be traced back to March, and they are conducting various investigations.
Last month, a report from a North Carolina clinician pointed out the inhalation of fatty substances in aerosolised oil, but a new study published this week by the Mayo Clinic found that patients' lungs were exposed to harmful fumes.
The Centers for Disease Control and Prevention (CDC) said that 18 deaths in 15 states are now positively associated with vaping, with a total of 1,080 patients, an increase of 275 since last week.