A large increase in Group A streptococcus bacteremia in the 2 month short period in 2024; report from a tertiary care hospital in Chiba, Japan

Following the COVID-19 pandemic, several European countries and the United States reported a marked increase in scarlet fever and invasive Group A streptococcus (GAS) infection.^{1, 2} Although this trend is likely because of reduced exposure and the immunity gap associated with a strict mask policy or social distancing during the pandemic, it is also thought to be related to the emergence and spread of the more toxigenic M1 UK variant.³ In Japan, an increasing number of cases of streptococcal toxic shock syndrome (STSS) caused by GAS have been reported since July 2023.⁴

In the first 2 months of 2024, a large increase in GAS bacteremia was detected at the Japanese Red Cross Narita Hospital, a tertiary teaching hospital with 710 beds. A total of six cases of bacteremia (2.37906 cases/1000 hospital admissions) were detected during the 2 months (Table 1). The median age was 45 years (range: 34–75 years). No patient was severely immunocompromised. The most common focus of infection was pneumonia with empyema (n = 3). The median Pitt bacteremia score and SOFA score were 2 and 3.5, respectively. Among six isolates from these cases, five were serotype T1 and positive for allele-specific PCR for the M1UK lineage.⁵ Two patients died within the first day of hospitalization, and most of the surviving patients required surgical intervention. Given this increase, we analyzed the distribution of cases of GAS bacteremia during 2016–2023. The average number of cases of GAS bacteremia per year was 3.25 cases during 2016–2019 (0.21125 cases/1000 hospital admissions) and 1.75 cases during 2020–2023 (0.11654/1000 hospital admissions), respectively.

Circulation of the M1_UK variant strain may have contributed to the large increase in STSS cases in Japan. Previous reports have suggested that the M1_UK lineage may drive the observed increase in GAS infections in Europe.³ In Japan, the M1_UK strains account for only 6.4% of all 780 strains collected at eight reference centers during 2018–2023, but nine out of 19 strains were found to be the M1_UK strains in reported STSS cases since August 2023 in the Kanto region.⁴ The incidence of GAS bacteremia in our hospital during the 2 month short period in 2024 was much higher than that before and during the COVID-19 pandemic, and most cases were caused by the M1_UK variant strain, which is consistent with the trend in the surveillance data shown above.

In conclusion, this report suggests that the M1_UK variant has been spread in certain areas in Japan and is likely to contribute to the large increase in invasive GAS infections.

Physicians should be cautious about this significant increase.

None.

The authors report that there are no competing interests to disclose.

This study was approved by the Ethics Committee of the Japanese Red Cross Narita Hospital under the condition that the confidentiality of all personal data be maintained (approval no: JRCNH-895-01).