Hundreds of people in Japan have been infected by a puzzling and potentially deadly “flesh-eating bacterium” in 2017.

In total, 525 patients with streptococcal toxic shock syndrome (STSS) were reported as of 10 December, according to the National Institute of Infectious Diseases – the highest number since record-keeping began in 1999.

The number of patients with STSS has been climbing each year but the cause for the increase remains unknown. The number of patients with STSS was just 203 in 2013.

STSS, which is fatal in almost one in three cases, destroys tissue and can result in death in a matter of days.

The infection is sometimes referred to as toxic shock-like syndrome (TSLS).

The disease is predominantly caused by a bacterium named Streptococcus pyogenes, commonly known as group A streptococcus.

The institute has warned people can die in the space of hours, from the onset from multiple organ failure and other symptoms after their bodies go into a critical period in a short amount of time.

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While it is thought that STSS starts in patients’ wounds that have become infected, there are many cases in which the path of the infection continues to be a mystery.

Besides from group A streptococcus, there are several other bacteria such as group G streptococcus which also engenders serious and even potentially life-threatening varieties of the disease.