Novel zoonotic Streptococcus suis lineage causes infective endocarditis with high mortality in Thailand.

Streptococcus suis (S. suis) is an important zoonotic pathogen that frequently causes meningitis, sepsis, infective endocarditis, and septic arthritis in humans. The objective of this study was to determine the epidemiological characteristics of S. suis infections in Nakhon Ratchasima Province, northeastern Thailand, between 2021 and 2023. A total of 448 cases of S. suis infection were reported in Nakhon Ratchasima Province, with cumulative incidences of 6.95, 5.09, and 5.15 per 100,000 population in 2021, 2022, and 2023, respectively. S. suis cases were occurred in all year. Infection caused by S. suis clonal complexes 1, 25, 104, 233, and the novel lineage ST1688 (serotype 2) which was significantly associated with infective endocarditis (IE) (OR = 2.96, 95% CI = 1.13-7.72; p-value = 0.027). Multivariate analysis demonstrated a significant risk of mortality associated with acute respiratory failure (OR 4.16, 95% CI = 2.15-8.08; p-value < 0.001) and IE (OR 2.05, 95% CI = 1.06-3.98; p-value = 0.033). Conversely, IE followed by valve surgery (OR 0.02, 95% CI = 0.00-0.08; p-value < 0.001) seemed to be a protective factor for patients with IE. This study revealed a high incidence of S. suis cases, in Nakhon Ratchasima, with a novel S. suis lineage associated with IE. Active surveillance and close monitoring of IE caused by S. suis should be prioritised.