The outbreak of lung illnesses linked to vaping grew by more than 200 cases in a week, now totaling 1299, with 26 deaths, the Centers for Disease Control and Prevention reported on Thursday.

The figures mean that 219 new cases and seven new deaths were reported. Cases have occurred in 49 states, the District of Columbia and the United States Virgin Islands.

A 17-year-old boy died in the Bronx last week, the youngest death so far linked to vaping. Utah and Massachusetts officials confirmed their states’ first vaping deaths this week.

The ages of those who died range from 17 years to 75 years, with a median of 49.

The exact cause of the illness is still unknown. Many of those who became ill had vaped THC, some had used both THC and nicotine, and others report vaping only nicotine.

Federal and state health authorities are testing vaping materials and studying tissue samples from patients in an effort to find the cause of the outbreak. They are particularly concerned about the huge amount of illicit THC products in circulation, which contain unknown mixtures of solvents, diluting agents and flavorings that may be toxic to the lungs.

The United States Army said it was treating two soldiers for vaping-related illness. The Army did not say what products the two soldiers had been using, according to an earlier report in The Wall Street Journal. The military has banned e-cigarettes from the exchanges on bases.

Health officials are urging the public not to vape, and emphasizing that those who choose to do so anyway should avoid THC, especially products sold on the street or the internet.

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