The U.S. Centers for Disease Control is investigating a "cluster" of lung illnesses that it believes may be linked to e-cigarette use after such cases were reported in 14 states.

The CDC said there was no evidence that an infectious disease was behind the illnesses and that more information was needed to determine whether they were in fact caused by e-cigarette use, also called vaping.

The CDC is working with health departments in Wisconsin, Illinois, California, Indiana and Minnesota on the investigation. Since June 28, states have reported 94 possible cases of severe lung illness tied to vaping, primarily among teenagers and young adults, according to a CDC statement on Saturday. Of those cases, 30 occurred in Wisconsin.

Patients experienced coughing, shortness of breath and fatigue. Some had serious breathing difficulties that required ventilation.

Last week, Children's Minnesota hospital said it was treating four teens aged 16 to 18. The patients did not respond to antibiotics, and doctors said the patients' lungs sustained some kind of injury and then the lungs began to fail.

"People have been vaping for years and so why are we seeing these injuries now?" pediatric pulmonologist Dr. Anne Griffiths told CBS News. "My biggest fear is we have been seeing them all along and we didn't know it because it looks so similar to common diseases."

A CDC spokesman was unable to provide additional information on the investigation.

Health Canada officials — having checked their databases of consumer product-related incidents and adverse reaction reports — said they did not find evidence of clusters of pulmonary disease cases related to vaping.

A spokesperson for Ontario's Lung Association said they're aware of news emerging from the U.S. on the links between e-cigarette use and severe lung illness.

"We haven't been seeing those types of stories here in Canada — yet," said Monica Kocsmaros.

"The rates at which youth are taking up vaping, both in the United States and here in Canada, should be alarming for everyone. We are starting to see the very real and detrimental effects vaping has on lung health. With vaping being a newer trend, evidence around its risks has been limited."

Kocsmaros called for more to be done to make vaping less accessible to youth.

Dr. Martin Kolb, director of the respirology division at McMaster University in Hamilton, Ont., says doctors there are keeping their eyes open for any similar cases.

"These incidents right now, they seem to describe something more acute, which is plausible from a health perspective," Kolb said.

His advice to teens and young people? "Don't use them. You don't know what is in there."

There's also no knowledge with respect to what temperature the devices vaporize at, or regulations on how they are manufactured, Kolb added.

"One would just hope that we don't make the same mistake that was done with cigarette smoking 50 years ago before people became aware of its harm."

Canadian ad restrictions proposed

In July, Health Canada released its consultation summary on proposed ad restrictions under the Tobacco and Vaping Products Act. The summary said all 13 provincial and territorial governments "strongly recommended immediate regulatory measures to reduce youth uptake of vaping products." They suggested the vaping advertising and promotion restrictions should align with those in place for tobacco products.

The "new e-cigarette rules are following due process and are not yet in effect," Health Canada spokeswoman Maryse Durette said in an email on Monday.

Separately, Health Canada is consulting on other measures to address the recent trend of youth vaping, such as examining the role of flavours, nicotine concentration and product design in making vaping products appealing to youth and non-smokers.

In the U.S., the CDC did not link the illnesses to any specific product. In the United States, Juul Labs, in which Altria Group Inc. has a 35 per cent stake, is the dominant e-cigarette maker.

"Like any health-related events reportedly associated with the use of vapour products, we are monitoring these reports," Juul Labs said on Sunday in a statement emailed to Reuters.

"These reports reaffirm the need to keep all tobacco and nicotine products out of the hands of youth through significant regulation on access and enforcement. We also must ensure illegal products, such as counterfeit, copycat, and those that deliver controlled substances, stay out of the market and away from youth."

Juul also noted that, according to some media reports, several incidences of lung illness linked to e-cigarette product use, have involved THC, found in marijuana, "a Schedule 1, controlled substance that we do not sell," the company said.

E-cigarettes are generally thought to be safer than traditional cigarettes, which kill up to half of all lifetime users, according to the World Health Organization.

But the long-term health effects of the nicotine devices remain largely unknown. In April, the U.S. Food and Drug Administration began an investigation into seizures among e-cigarette users.