The number of possible cases of vaping-related lung illnesses being investigated has nearly doubled since last week, and health authorities are looking into the role of contaminants or counterfeit substances, the Washington Post reports.

• That's partially because of how suddenly these illnesses have appeared, as vaping products have been on the market for years.

What they're saying: State and federal health officials say Americans should stop vaping altogether until the source of the illnesses is discovered.

• Some officials are focused especially on THC products.

The bottom line: "When you heat a substance, you release chemicals," said Robin Deterding, chief of pediatric pulmonary medicine at Children's Hospital Colorado, per NBC News. "This is a chemistry experiment that you keep inhaling."

Speaking of vaping, yesterday was a wild news day for Juul.

• It began with the news that Juul is pushing a new age-verification system in retail stores, but then devolved into a new public relations crisis when news broke that the company is being investigated by the Federal Trade Commission and has been linked to seizures.

The big picture: Juul is now not only facing accusations that it fueled the rise of teen vaping, but also that it potentially presents serious health risks to adult users.

Juul's good news: The company announced yesterday that it's rolling out a new checkout system that would crack down on teenagers purchasing its products, as WSJ first reported.

• It's offering retailers more than $100 million to incentivize them to install the new electronic age-verification system.
• No one would be allowed to buy Juul products in store without scanning some kind of identification.

Juul's bad news: It's being investigated by the Federal Trade Commission for its marketing practices, the Journal also reported. The agency is investigating whether Juul targeted minors, and the FTC could end up seeking monetary damages.

• Juul was also cited in 3 seizure reports that triggered the FDA's investigation into whether e-cigarettes can cause seizures, Bloomberg reported. This is the first time vaping-related seizures have been specifically tied to Juul devices.
• But, the FDA wasn't able to officially confirm that 2 of the 3 reports were actually linked to Juul. People often refer to vaping generically as "Juuling."

Some stores have already voluntarily limited or ended e-cigarette sales, and San Francisco recently became the first city to ban e-cigarette sales.

• If Juul can't prove it's a net positive for public health, it's got a lot to lose.

Envision Healthcare and TeamHealth, two of the largest firms that provide physician services to hospitals, are sitting on loans that investors increasingly believe will be more difficult to pay back if Congress enacts reforms to out-of-network billing.

Driving the news: Credit rating agency Fitch placed a $5.4 billion loan from Envision and a $2.7 billion loan from TeamHealth on its "loans of concern" list this week. Investors willing to buy up either company's debt are paying less than 81 cents on the dollar, according to the Financial Times.

• "Envision, like other health care companies, has been pressured by uncertainty over the outcome of political efforts to cut medical bills," Fitch analysts wrote in the report.

Thought bubble, per my colleague Bob Herman: Envision and TeamHealth, both now owned by private equity firms, have been known to engage in surprise billing and have argued they have converted almost all of their business to in-network terms.

• But those companies are fighting federal reforms hard, and now investors think the end of surprise billing will degrade their businesses.

Maine is the latest state to start taking more responsibility for its own Affordable Care Act exchange, Axios' Sam Baker writes.

• Gov. Janet Mills wants to join the ranks of states using a hybrid model, in which Maine would run its own outreach and marketing efforts but continue to use HealthCare.gov.
• Modern Healthcare notes that 4 other states have made similar moves recently: Nevada, New Jersey, New Mexico and Pennsylvania. Oregon is also thinking about it.

Sam's thought bubble: This is still a far cry from the initial idea for the exchanges, which envisioned most states running their own with only a limited federal fallback. 

• Instead, most states use HealthCare.gov — in part because, in one of the great ironies of the ACA, Republican governors in the early days refused to implement the ACA and therefore handed their states' systems over to the federal government.
• For a handful of blue states to partially wade back into their own operations is a bit of a microcosm of the law's overall standing: Democrats care more about making it work but the larger lay of the land is pretty well fixed.

Immigrants battling severe illnesses who would ordinarily be given special, temporary protection from deportation have been told those protections are no longer available and they must leave the U.S. within 33 days, according to letters sent by U.S. Citizenship and Immigration Services (USCIS) and first reported by WBUR.

Why it matters: USCIS has since said that Immigration and Customs Enforcement (ICE) will now oversee the "medical deferred action" program — a change that had not been formally announced, my colleague Stef Kight writes.

• An ICE official told the New York Times that the agency "had no idea" about the change, nor is it prepared to handle the new responsibility.
• Medical deferred action allows immigrants who are receiving treatment for serious medical conditions such as cancer, cystic fibrosis, cerebral palsy and muscular dystrophy to stay in the U.S. temporarily without fear of deportation. Family members can also receive this deferred action.
• There are around 1,000 applicants for the 2-year program each year, according to the Times.

What they're saying: "Because USCIS is not an enforcement agency, it is not appropriate for us to adjudicate requests for suspended enforcement not clearly assigned to us in law or policy," an agency spokesperson told Axios.