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The recent warning from Tokyo public health officials regarding the of invasive group A Streptococcus infections, including cases of streptococcal toxic shock syndrome (STSS), raises important questions regarding the epidemiology of this severe infection.

A Fulminant Infection

STSS is best understood as a group A streptococcal infection -- of any sort -- that causes shock and organ dysfunction. As an infectious disease, emergency medicine, and critical care physician, I have seen several cases of STSS. Often, I have been consulted for what initially appeared to be a simple streptococcal bacteremia, but the simplicity has quickly evaporated. Each time I have confronted STSS, I have been struck by the ferocity of the infection, its rapidity, and the ability to impair the function of vital organs. To me, it has always been akin to a tornado ripping through a body with physicians scrambling to stay a few steps ahead.

Those steps include treatments such as antibiotics, aggressive ICU-level care, possible surgical debridement or drainage of sites of infection, and administration of intravenous immunoglobulin (IVIG) in an effort to control the storm of deranged physiology. Even with modern interventions, mortality rates can reach 30%.

The Situation in Japan

In the just over 3 months of 2024 that have elapsed, Japan has reported more than 500 cases of STSS (already more than half of the record high from 2023). STSS cases seem to be linked to skin and soft tissue infections, though a group A streptococcal infection of any site can precede the aberrant immune reaction that characterizes STSS. Why some group A Streptococcus infections lead to STSS -- and some do not -- remains to be discovered.

The cases in Japan are linked to a particular strain of group A Streptococcus . This strain is known to be hypertoxigenic, is considered highly transmissible, and has been worldwide. Beyond issuing warnings, Japan is encouraging people to take preventive steps to avoid infection and has reportedly canceled certain large-scale events.

Underlying Causes

It is unclear what factors are behind the changing epidemiology of STSS and invasive group A Streptococcus infections. Possibilities include heightened diagnosis or increased attack rates following the COVID pandemic, as the pool of susceptible individuals increased since streptococcal infections fell due to the social distancing that occurred during the pandemic.

Indeed, also saw a "catch up" of streptococcal infections post-pandemic (also linked to M1UK). To fully explain the phenomenon occurring in Japan, it is therefore important to understand the carriage rates of the M1UK strain in the country. Carriage is a likely precursor to, reservoir of, and source of infection. If carriage rates have increased, that may signify a change in the epidemiology of Streptococcus, and high-risk carriers could possibly be decolonized.

Implications for U.S. Clinicians

Post-pandemic, the heightened group A streptococcal infections. Japan's experience may simply be reflective of its own post-pandemic surge. Surveillance in the U.S. for both invasive group A streptococcal infections and STSS should continue, with strain characterization.

However, it is important that clinicians throughout the world be alert to the features of STSS, and familiarize themselves with treatment regimens, especially the use of IVIG to forestall the severe consequences that are characteristic of this infection. In my experience, STSS is an entity that is not fully appreciated by clinicians for the emergency that it is, as it is often overshadowed by staphylococcal toxic shock syndrome and lumped in as an ordinary form of sepsis. The events in Japan should serve as a reminder to clinicians globally regarding this challenging infection.

is a senior scholar at the Johns Hopkins Center for Health Security, and a practicing infectious disease, critical care, and emergency physician in Pittsburgh.

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