Cases of a dangerous and highly fatal bacterial infection have reached record levels in Japan, official figures show, and experts have so far been unable to pinpoint the reason for the rise.
As of June 2, Japan’s Ministry of Health had recorded 977 cases of streptococcal toxic shock syndrome (STSS), which has a mortality rate of up to 30%. Some 77 people died from the infection between January and March, the latest figures available.
Japan’s ongoing outbreak has already surpassed last year’s previous record of 941 preliminary infections – the highest since statistics began in 1999. Japan’s National Institute of Infectious Diseases reported 97 deaths due to STSS last year, the second highest number of deaths in the last six years.
STSS is a rare but serious bacterial infection that can develop when bacteria spread into deep tissues and the bloodstream. Patients initially suffer from fever, muscle pain and vomiting, but symptoms can quickly become life-threatening with low blood pressure, swelling and multiple organ failure as the body goes into shock.
“Even with treatment, STSS can be deadly. Out of every 10 people with STSS, up to three people will die from the infection,” according to the U.S. Centers for Disease Control and Prevention (CDC).
Most cases of STSS are caused by the bacteria group A streptococcus (GAS), which mainly produces fever and strep throat in children. In rare circumstances, streptococcus A can become invasive when the bacteria produces a toxin that allows it to gain access to the bloodstream, causing serious illnesses such as toxic shock.
Strep A can also cause “flesh-eating” necrotizing fasciitis, which can lead to limb loss. However, most patients who contract this disease have other health factors that can decrease their body’s ability to fight infection, such as cancer or diabetes, according to the CDC.
Invasive group A streptococcal infections were largely controlled by Covid-19 controls such as mask-wearing and social distancing, but after these measures were relaxed, many countries reported an increase in the number of cases.
In December 2022, five European countries reported to the World Health Organization an increase in invasive group A streptococcus (iGAS), with children under 10 years old those most impacted. The CDC said it was also investigating an apparent increase in the disease at the time.
In March, Japanese authorities warned of a rise in STSS cases. National Institute of Infectious Diseases of Japan released a risk assessment stating that the number of STSS cases caused by iGAS “has increased since July 2023, especially among those under 50 years of age.”
The CDC states that older people with open wounds are at greater risk of contracting STSS, including those who have recently had surgery.
“However, experts do not know how the bacteria entered the bodies of nearly half of the people who contract STSS,” the CDC said on its website.
The reason for this year’s rise in STSS cases in Japan is still unclear, according to Japanese public broadcaster NHK.
Professor Ken Kikuchi of Tokyo Women’s Medical University told NHK the increase could be due to people’s weakened immune systems post-Covid.
“We can increase immunity if we are constantly exposed to bacteria. But this mechanism was absent during the coronavirus pandemic,” said Kikuchi. “Therefore, more people are now susceptible to infection, and this may be one of the reasons for the sharp increase in cases.”
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