Story highlights An alarming rise in scarlet fever cases has English officials worried

Researchers search for the cause of the outbreak and urge caution globally

(CNN) The age-old killer scarlet fever is on the rise in England and East Asia, according to research published Monday in The Lancet Infectious Diseases journal, and investigators don't know why.

"Whilst current rates (in England) are nowhere near those seen in the early 1900s, the magnitude of the recent upsurge is greater than any documented in the last century," said study author Theresa Lamagni of Public Health England, the agency that funded the analysis. "Whilst notifications so far for 2017 suggest a slight decrease in numbers, we continue to monitor the situation carefully ... and research continues to further investigate the rise."

Identified by a bright red rash that looks and feels like sandpaper, scarlet fever is a highly contagious disease caused by the same bacteria behind strep throat, group A Streptococcus pyogenes.

Historically a common cause of childhood death, scarlet fever had been declining over the past two centuries, according to the study, with any rise in cases typically following a "natural cyclical pattern" every four to six years.

But since 2009, cases have been steadily increasing in several East Asian countries, including Vietnam, South Korea, Hong Kong and mainland China.

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