Dangerous new strains of a “hypervirulent” superbug have been found in 16 countries, including the United States, the World Health Organization (WHO) announced in a new report.The superbug, known as hypervirulent Klebsiella pneumoniae (hvKp), is a type of drug-resistant bacteria that can cause rapidly progressing, deadly infections, even in people with healthy immune systems.In general, K. pneumoniae can be found in the environment — for example, in soil and water — as well as in the upper throat and gastrointestinal tract of various animals, including humans. The classic version of the germ is a big problem in health care settings, where it can contaminate medical equipment and cause opportunistic infections, especially in people with weak immune systems. It’s known to cause pneumonia, urinary tract infections, bloodstream infections and the nervous-system infection meningitis.At baseline, the bacteria are inherently resistant to the antibiotic ampicillin, and in recent years, they’ve developed resistance to more and more drugs.Related: Superbugs are on the rise. How can we prevent antibiotics from becoming obsolete?The newer, “hypervirulent” variety of K. pneumoniae poses a wider threat because it can cause severe infections even in people with healthy immune systems. The invasive infections can progress very quickly, spurring a high rate of complications and death, according to CIDRAP News, which is published by the University of Minnesota.When these hvKp strains were initially discovered in Asia in the 1980s, they were still vulnerable to a variety of antibiotics. But now, the strains have spread globally and show resistance to both older and newer classes of antibiotics, studies suggest. In particular, it’s concerning that some of these strains show resistance to carbapenems, a class of antibiotics often used to treat bacterial infections that are resistant to multiple other drugs.Get the world’s most fascinating discoveries delivered straight to your inbox.”When you couple carbapenem-resistance with the hypervirulence exhibited by certain strains of K pneumoniae it is a recipe for increased morbidity and mortality from this bacterium,” Dr. Amesh Adalja, a senior scholar at the Johns Hopkins University Center for Health Security, told CIDRAP News.The WHO’s report is a result of the agency requesting information from its member states regarding the global prevalence of K. pneumoniae. The request yielded data from 43 countries and territories; of those, 16 reported detecting hvKp. Twelve of the reporting countries said they’d found a particularly concerning strain of the bacterium dubbed ST23, which carries genes that enable it to resist carbapenems and all available beta-lactam antibiotics, the WHO said in a July 31 statement.The U.S. was among the countries that reported detecting hvKp bacteria, in general, but not ST23, specifically.Globally “the prevalence of hvKp-associated infections may be underestimated” due to current limitations in the surveillance for these germs, the WHO said in the statement. The agency flagged a need to improve awareness about these infections and to expand testing for them. That’s important for tracking the superbug within the population as a whole and for treating individual patients, because correctly identifying the bacteria is important for selecting the correct treatment course, the agency said.”With the concurrence of hypervirulence and antibiotic resistance, it is expected that there will be an increased risk of spread of these strains at both the community and hospital levels,” the WHO concluded.Ever wonder why some people build muscle more easily than others or why freckles come out in the sun? Send us your questions about how the human body works to community@livescience.com with the subject line “Health Desk Q,” and you may see your question answered on the website!