HELENA, Mont. (AP) — Montana health officials have asked residents to consider not using e-cigarettes while a national investigation into its implications is underway.

The state Department of Public Health and Human Services says serious lung-related illnesses are possibly linked to e-cigarettes, also known as vaping.

Health officials say 33 states have identified 450 potential cases of severe pulmonary illnesses possibly linked to e-cigarette use as of Sept. 6 including five deaths.

Officials say that number continues to grow.

Officials say Montana has not reported a confirmed case, but potential cases are currently being investigated in the state.

The owner of one vaping business says problems have arisen with black market product purchases.

Symptoms could include coughing, shortness of breath, chest pain, and fatigue and can worsen over a short period of time.