Scientists call for improved Streptococcus suis surveillance

Scientists have suggested making Streptococcus suis infections reportable in Europe to improve surveillance, given the severity of the disease.

Researchers surveyed seven reference laboratories and reviewed the scientific literature to increase insight into the epidemiology of human Streptococcus suis infections in Europe.

They identified 236 such infections and an additional 87 by scanning the literature. The team performed genome sequencing of type 46 isolates and combined them with 28 publicly available genomes. Findings were published in the Emerging Infectious Diseases journal.

Streptococcus suis infections occur through direct contact with infected pigs and consumption of undercooked contaminated pork. Human infections have become endemic in Thailand and Vietnam, driven by eating traditional raw pork dishes. In Thailand, Streptococcus suis is a reportable disease.

European situation
In Europe, infections are considered an occupational hazard, mainly occurring among people with skin lesions working with pigs or pork products. Carriage in healthy people or human-to-human transmission has not been reported to date. Incidence is likely underestimated because Streptococcus suis infections are not a notifiable disease.

Reference labs in Spain, Germany, Netherlands, Denmark, Czech Republic, Poland, and the United Kingdom reported 107 cases of human Streptococcus suis infections from 1990 to 2018.

Scientists got data from 129 Streptococcus suis infections reported in 69 research articles. Combining both sources, 236 European cases from 1990 to 2022 were identified.

Germany, Spain, and the Netherlands, the top pig-rearing countries in Europe, reported 114 of the 236 cases.

Most patients were middle-aged men. Meningitis was the primary clinical syndrome, followed by sepsis. Additional signs and symptoms included hearing loss, endocarditis, and spondylodiscitis; 11 people died. Patient occupation was described as a potential risk factor in 19 cases in the survey and 72 cases in the systematic review. Scientists said European educational campaigns should be tailored to the different at-risk populations.

Underestimation of cases
Although France has one of the largest pig populations in Europe, only seven human cases have been reported. However, despite having smaller pig populations, the Czech Republic reported 18 and Poland 22 instances. Scientists also found evidence of underreporting in the Netherlands.

Differences in exposure routes have led to differences in epidemiology; multiple foodborne Streptococcus suis outbreaks with high levels of illness and death have occurred in southeastern Asia in the past two decades. In Thailand, educational campaigns targeting at-risk populations have reduced the incidence of infections.

The UK was the only country that included human Streptococcus suis infections in official government reports. From 1991 to 2017, 61 infections were recorded. These reports contained ten times as many cases within the same timeframe as UK cases from the survey and systematic review combined because these did not capture many unpublished cases. This suggests the number of cases seen in other countries through the survey might also be underestimated, said scientists.

There was an increase in reported cases after 1999; however, this could have been caused by heightened awareness after a severe outbreak in China in 2005 and by more precise bacterial identification techniques.

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