CHICAGO (Reuters) – U.S. health officials on Thursday reported another 180 cases of vaping-related lung illnesses and announced plans to start testing aerosols produced by e-cigarettes and vaping products as they search for the source of the nationwide outbreak that has so far killed at least 33 people in 24 states.

The U.S. Centers for Disease Control and Prevention (CDC) also said it plans to start testing lung tissue and fluids collected from people who became sick in the outbreak. The CDC said the new testing may lend insight into chemical exposures contributing to the outbreak.

The CDC now reports 1,479 confirmed and probable U.S. cases of the mysterious respiratory illness tied to vaping, up from 1,299 a week ago, an indication that the public health crisis has shown no sign of slowing.

Last week, the CDC and the U.S. Food and Drug Administration said that while many patients became ill after vaping products containing THC, the psychoactive ingredient in marijuana, some had only used nicotine vape products. They said more than one root cause may be behind the outbreak.

Investigators primarily have been testing the liquids in vape products. Testing the aerosol produced after the liquids are heated might show whether that causes a chemical reaction that produces a toxic substance. [Read More @ Reuters]