This study aim to test the hypothesis that human S.suis infections are associated in time and space with outbreaks of Porcine Reproductive and Respiratory Syndrome (PRRS) virus or other diseases in pigs.

Streptococcus suis is a zoonotic agent which can cause severe systemic infection in humans exposed to infected pigs or pig derived products. Over 700 cases have been reported worldwide, most of them were in China and Vietnam in the last few years.

In Vietnam, S. suis infection in adults is common, and patients with S.suis are often admitted to the National Hospital for Tropical Diseases (NHTD), a tertiary referral hospital for infectious diseases in northern Vietnam. In 2007, 50 laboratory confirmed cases with S.suis were reported at this hospital, and in 2010, 65 laboratory confirmed S.suis cases have been identified by September. Pig breeding and pork consumption is popular in Vietnam, with the majority of pigs and meat supply channelled from small-scaled un-controlled farmers and slaughterhouses, which pose a great potential health risk to people involved in the chain. A case-control study conducted in southern Vietnam showed that occupational exposure, raising pigs at home and consuming high-risk dishes from pigs significantly increased the risk of S. suis infection.

It has been suggested that the incidence of human S. suis cases is possibly linked to the occurrence of Porcine Respiratory and Reproductive System (PRRS) virus outbreaks in northern Vietnam. In 2010, the disease has spread to over 30 provinces over the country, with many outbreaks reported in northern provinces in the period from April to July. Field observations in other countries showed that PRRS virus infection increased pig's susceptibility to S. suis infection, including serotype 2 and 7. Therefore, PRRS virus outbreaks might have increased the risk of S. suis transmission to humans through exposure to pigs with PRRS virus infection and concomitant S. suis disease. Nevertheless, sufficient data are not available to confirm or refute this hypothesis. Knowledge of spatial and temporal relationships between human S.suis infections and disease outbreaks in pigs can increase our understanding of risk factors for human S.suis infection and support disease prevention and preparedness in the community.

Group 1: cases

Inclusion Criteria:

• Date of specimen (blood or CSF sample) collection is between 01/01/2010 to 31/12/2010; and
• S.suis infection confirmed by either CSF or blood culture or PCR; or
• Meet the criteria for a probable case as above (in absence of laboratory confirmation).

Exclusion Criteria:

- Unable to collect patient's spatial data at commune level.

Group 2: controls

Inclusion Criteria:

• Diagnosis as sepsis at hospital admission (based on clinical symptoms or laboratory evidence)
• Admission date between 01/01/2010 and 31/12/2010

Exclusion Criteria:

• Symptoms of meningitis
• Clinically a high suspicion of S. suis infection (culture and PCR negative) as determined by doctor.
• Laboratory culture or PCR result positive for S.suis infection
• HIV infection
• Unable to collect patient's spatial data at commune level

Population under study is the population from which cases of S.suis infection admitted to NHTD arise. Sepsis patients are selected to present the population of interest under the following assumptions:

• they are representative of the background exposure rate of the population from which cases come from,
• their diagnosis is independent of the exposure of interest,
• they are similar to the S.suis cases in terms of care seeking and referral patterns.