Mystery Rise in Infection With 30% Fatality Rate Sweeps Japan

There has been a massive surge in cases of a life-threatening form of bacterial infection in Japan that has left officials investigating the cause of the increase.

The nation’s National Institute of Infectious Diseases (NIID) has recorded a significant rise in cases of streptococcal toxic shock syndrome (STSS) predominantly caused by the bacteria that causes strep throat and impetigo—Group A Streptococcus.

STSS is caused by the bacteria reaching deep into the body—including the blood and deep tissue—and triggering low blood pressure that can ultimately lead to organ failure. In Japan in 2023, 30.9 percent of cases among those aged under 50 resulted in death, though the New York Department of Health says that up to 60 percent of STSS cases can result in death.

The rise in STSS cases has come in at the same times as a rise in severe invasive streptococcal infections in the country.

In 2023, there were 941 severe streptococcus infections—the highest since before the coronavirus pandemic. In the first 10 weeks of 2024, there have already been 474 infections, according to NIID figures.

Japan Strep A
People wearing face masks walk down Takeshita Street in the popular Harajuku area of Tokyo on September 23, 2022 and, inset, a visual representation of Streptococcus bacteria. Japan has seen a rise in cases of…

RICHARD A. BROOKS/AFP via Getty Images

In January, the NIID said that between January and December 17 of last year, there had been 340 cases of STSS, of which 97 resulted in death. This was the second-highest total since 2019, when 101 people died, but the highest proportion of STSS cases in six years.

The agency has not given a sense of the proportion of severe invasive streptococcal infections that have progressed into STSS so far in 2024. Figures from local authorities, however, suggest the high rates of progression are continuing to occur.

From March 11-17, the Tokyo Metropolitan Government recorded six cases of fulminant hemolytic streptococcal infection—rapidly progressing septic shock caused by the bacteria—one of which had resulted in death. Half of those cases had been caused by Group A Streptococcus, and all but one were among those aged 60 or over.

While STSS is thought to more commonly affect those aged over 65, the NIID said that from July 2023 onwards, the rise in cases was primarily among those under 50. The age group had also seen an increase in the proportion of deaths.

The sudden surge in cases appears to be a result of the loosening of COVID-19 measures that would have prevented infections of other diseases, according to a comments from Japan’s health minister Keizo Takemi, according to the Japan Times.

Japanese media reported health officials urging the public to continue washing their hands regularly and tending to wounds, which can serve as infection sites.

David Katz, emeritus professor of immunology at University College London, told Newsweek that while a relaxation in sanitary measures following the pandemic would account for the rise in infections, the increase in the severity of the cases might be explained by the “old hygiene hypothesis.”

“You’ve maintained your immunity to Strep A by being exposed to it all the time, and all of a sudden you weren’t exposed to it for a number of years [during the pandemic]—so now when you get it, you get it without any immunity,” he said.

While Katz said the increase in the proportion of people under 50 getting STSS was “quite hard to explain,” he suggested the lack of exposure during the pandemic followed by increased socializing after restrictions were lifted may play a role.

“The under 50s are the ones who are going to be more sociable and more likely to go to parties where they get Strep A, I suppose,” he said.

The NIID said that sampling of STSS cases had found that while 76.7 percent were due to conventional strains, 28.3 were the M1 strain which is more prevalent in Europe, North America and Australia. Around a quarter were of a particular lineage that became prevalent in the United Kingdom in the 2010s.

The NIID said the U.K.-specific strain had been growing in prevalence in Japan since 2019 and, since August, had been responsible for an accumulation of STSS cases in the Kanto region, which includes Tokyo.

However, it added that though the U.K. strain was “highly transmissible,” the relationship between this increase in the number of STSS cases remained “unclear” and would require further investigation and sampling.

Katz said that a return of international travel was unlikely to have contributed to the increased prevalence of the M1 strain.

He described the presence of the strain as “interesting, but not important” in understanding the rise of severe cases, as it had been in circulation for decades and would likely have exhibited a similar effect elsewhere before—but said that longer-term study would be required to know what had contributed to them.