(Reuters) - Three young people have been hospitalized with kidney failure and a dozen others sickened in Casper, Wyoming, in an outbreak linked to a batch of the designer drug Spice, authorities said on Friday.

State medical officials said the cause of the outbreak was under investigation but reported that Casper residents who have sought medical treatment for vomiting and back pain had recently smoked or ingested a chemical-laced herbal product packaged as "blueberry spice."

The illnesses reported by physicians and hospitals in the east central Wyoming city beginning on Sunday had added up to a cluster that alarmed health officials by the end of the week.

"At this point, we are viewing use of this drug as a potentially life-threatening situation," Tracy Murphy, Wyoming state epidemiologist, said in a statement.

Those who have fallen ill range in age from late teens to early 20s and all used blueberry-flavored spice, said Bob Herrington, director of the Casper-Natrona County Health Department.

Warnings about the product and a list of symptoms associated with kidney malfunctions have been posted in health departments, clinics and medical facilities across the state even as scientists at the Wyoming State Crime Laboratory scrambled to ferret out the compounds in the batch suspected in the incident.

Harrington said the outbreak was causing concern among health and law enforcement officials in the city of 55,000 residents.

"Based on our information from the doctors, the three people with kidney failure are in pretty serious shape; they're very sick," he said.

Spice is sometimes sold as "legal marijuana" because of the high that users experience from plant material coated with chemicals that claim to mimic THC, the active ingredient in marijuana, according to the U.S. Drug Enforcement Administration.

Drug policy experts said use of spice has been on the rise since the DEA in 2009 tracked skyrocketing numbers of reports about the products from poison control centers, hospitals and local law enforcement agencies.

The DEA extended a ban on Thursday on five chemicals that make some spice mixtures illegal. Yet authorities have struggled to keep pace with changes in the chemical make-up of the designer drugs, which sometimes skirt newly enacted laws.

Bans on spice are in place in several states, including Wyoming. But with manufacturers capable of rapidly adjusting recipes, states like Idaho have made illegal whole groups of compounds rather than specific chemicals.

"Spice is a pretty lucrative business and the marketing is to youth," said Caitlin Zak, program manager for the Idaho Office of Drug Policy.

(Editing by Dan Whitcomb and Cynthia Johnston)

[Image via Shutterstock.com.]

Mochila insert follows ...