Over this 10-year period, nine patients with S. suis infections were identified at tertiary medical institutions on Jeju Island (Table 1). The first case occurred in 2014, followed by a 5-year gap until the second case emerged in 2019. Since then, new cases were reported annually until 2023. These cases exhibited distinct epidemiological and clinical patterns, reflecting local occupational and cultural practices. Most patients were male (7/9), and nearly half (4/9) were aged 65 years or older. Two patients were pig farmers, while the others had diverse occupations, including bus driver, housekeeper, office worker, and crop farmer. Notably, two patients had consumed raw pork products (aejeohoe) and one had consumed raw horse meat. Five patients lacked sufficient medical records regarding contact with pigs.

Fever was a common initial symptom among patients, often accompanied by vomiting, joint pain, headache, and altered consciousness. S. suis was isolated from the blood samples of eight patients and the cerebrospinal fluid of one patient. All isolates were susceptible to penicillin, ampicillin, ceftriaxone, levofloxacin, moxifloxacin, tigecycline, and vancomycin but resistant to tetracycline, clindamycin, and erythromycin. Initial laboratory findings revealed elevated creatinine (5/9), liver enzyme (6/9), and C-reactive protein (8/9) levels. Procalcitonin levels were markedly elevated (>100 ng/mL) in two cases. Six patients showed thrombocytopenia (platelet count <150×10³/μL), with two showing a severe platelet count reduction to 5×10³/μL, indicating significant hematological complications.

All patients received antibiotics, with ceftriaxone the most commonly used. Combination therapies involving vancomycin, levofloxacin, or piperacillin/tazobactam were used in severe cases. Complications included central nervous system (CNS) infections in three patients (two meningitis and one subdural empyema), pneumonia in two, septic shock in two, infectious spondylitis in one, and streptococcal toxic shock syndrome in one. Three survivors with CNS infection experienced persistent hearing loss. The mortality rate was 2/9, with both fatalities occurring within 24 hours of admission. Both fatal cases involved patients who recently received AstraZeneca COVID-19 vaccinations. These cases were initially misattributed to vaccine-related adverse events but were ultimately diagnosed as S. suis septic shock through blood culture.

Human S. suis infections often stem from close contact with pigs or consumption of undercooked pork [1]. On Jeju Island, pig farming and pork production are major industries, with a local custom of eating raw piglets, which increases the exposure risk [3,4]. The analysis revealed that direct contact with pigs and raw pork consumption were the primary transmission routes. Two patients reported direct occupational contact with pigs and two reported consuming raw pork products, highlighting the role of occupational exposure and dietary habits in disease transmission. Geographically, the patients were distributed between Jeju City and Aewol-eup. Pig farm mapping showed no direct correlation between pig farm density and human S. suis infection area. However, as human infections are linked to contact with pigs, further cases are likely with the expansion of the pig industry (Fig. 1).

Public health measures are essential for reducing S. suis infection in humans. Targeted strategies should focus on high-risk groups such as pig farm workers, pig handlers, slaughterhouse and meat processing employees, food service workers handling raw pork, and the general public, particularly those consuming raw pork. Effective interventions include educational materials on S. suis transmission, symptoms, and prevention, as well as hygiene posters, campaigns such as ‘One Health’ linking human, animal, and environmental health, and mandatory safe handling training. Personal protective equipment, including gloves, face shields or goggles, waterproof aprons or gowns, boots, and masks is vital for those in direct contact with pigs or raw pork. Study limitations include incomplete documentation of contact with pigs in five patients, limiting precise exposure assessment. In summary, S. suis infections on Jeju Island mainly affected pig farm workers and raw pork consumers. Ongoing monitoring and preventive education are crucial for reducing risk. Healthcare providers should highly suspect S. suis infection in patients with meningitis or sepsis, especially if they report a history of contact with pigs or raw pork consumption.