Cases of lung illness and deaths from vaping have tapered off since peaking in September, health officials said on Thursday, but the outbreak also reached a grim new milestone: The youngest death, of a 15-year-old, was reported by Dallas County Health and Human Services.

The teenager had “a chronic underlying medical condition,” Texas officials said in a statement on Dec. 31, but they did not identify the condition, the patient’s gender or what products the patient had been vaping.

“Reporting a death in a teen due to Evali is so tragic,” Dr. Philip Huang, the Dallas County health director, said in a statement, referring to the official name for the disorder, E-cigarette or Vaping-Associated Lung Injury. “We are seeing that severe lung damage, and even death, can occur with just short-term use of these products.”

The statement said that one teenager in the Dallas area who was hospitalized with the illness reported having vaped for only one month.