Streptococcus suis, a zoonotic pathogen that naturally inhabit the upper airways, gastrointestinal tract and genitals of pigs [
11], can cause a wide variety of diseases in pigs and humans, including meningitis, septicemia and endocarditis. In human beings, the most common manifestation of
S. suis infection is meningitis, with sepsis ranking the second common disease [
12,
13]. Hearing loss is the most common sequela after recovery from purulent meningitis, whereas death often follows septic shock [
3]. Compared with meningitis and sepsis, other clinical presentations, including enteritis, arthritis, endocarditis, pneumonia, spondylodiscitis, endophthalmitis, uveitis and peritonitis, are less common [
13]. Initially in this case, the patient presented with typical meningeal signs, such as headache, fever. Signs of spinal canal infection occurred on the 5th day of disease onset, manifesting as Lower back pain, which led the physician to suspect meningitis and perform a lumbar puncture, thus helping find the infectious agent. Epidemiologic history, Metagenomic next-generation sequencing and MRI scan together helped confirm that this is a case of
S. suis infection that manifested as spinal canal infection. Epidemiology history, such as close contact with sick pigs or pork, is very useful in diagnosing
S. suis infection [
3]. In the outbreaks of
S. suis infection that occurred in China, almost all the human patients had a history of direct contact with infected pigs or pork [
3]. However, there are several cases that develop
S. suis infection without known history of pig contact [
14,
15]. As with many bacterial infections, the confirmation of
S. suis infection relies on the isolation of the infectious agent from normally sterile body fluid, including blood and cerebrospinal fluid. But the sensitivity of these standard microorganism diagnostic methods is not that satisfying and is affected by antibiotics use prior to sample obtaining, which has been well elucidated in bacterial meningitis [
16‐
18] Traditional serotyping methods such as coagglutination or agglutination tests using serotype-specific antisera are simple, but the production of specific antisera is time-consuming, expensive, laborious, and only available in reference laboratories. Cross-reaction also occurred in some serotypes. So Traditional diagnostic methods are routine, sophisticate, and sometimes insensitive to adequately diagnose the infectious agents [
19]. To better identify the causative agents, several molecular biological techniques such as PCR, real-time PCR or WGS have been applied for diagnosis [
19‐
21]. A study designed to verify the usefulness of multiplex PCR in identifying
S. Suis infection demonstrated that this technique can detect
S. suis directly from positive hemocultures and CSF, with high sensitivity, specificity compared to culture and serotyping methods. In addition, mNGS, an unbiased approach that is able to detect many potential infectious agents in a single array [
22], represents a promising one. A study published in 2019 to verify the real-life usefulness of mNGS in intracranial infection indicates that clinical metagenomic NGS of CSF represents a potential step forward in the diagnosis of meningoencephalitis [
22]. In
S. suis infection, there are also several case reports making use of mNGS to identify
Streptococcus suis in cerebrospinal fluid and blood samples [
21,
23] It is worth noting that in these cases, conventional microorganism detection methods are usually negative. But currently it remains difficult to roll out this technology in countries with limited resources. A previous study developed the immunochromatographic banding (ICS) technique to detect
S. suis antigens in urine and could be a good option for rapid diagnosis [
24]. But results of this study need to be further verified.
It is generally thought that
S. suis zoonoses result from a wound infection or ingestion of pork contaminated with this pathogen. Raw pork consumption, exposure to pigs or pork, pig-related occupation, male sex are the main risk factors of
S. suis infection [
25]. A case–control study conducted in Vietnam suggests that risk factors of
S. suis infection include eating “high risk” dishes, including such dishes as undercooked pig blood and pig intestine, occupations related to pigs, and exposures to pigs or pork in the presence of skin injuries [
26]. In addition to direct contact with infected pigs or contaminated pork, growing evidence have supported that
S. suis can also be an airborne pathogen [
27‐
29]. As for the transmission route of
S. suis in this patient, although the patient had no apparent wounds on his hands or other parts of his body that may predispose him to
S. suis infection, he did develop such an infection. According to the patient’s initial symptoms such as sore throat and dry coughing, a rational explanation is that the pathogen entered the host through inspiration and invaded the host through respiratory tract mucosa, just as it usually does in pigs, indicating that this zoonotic agent has become much more adaptive to humans.
In conclusion, this is a rare case that manifested as spinal canal infection caused by S. suis. Although S. suis can cause systematic infection, spinal canal infection is an uncommon disease in S. suis infection. To the best of our knowledge, there are few reports about this disease caused by S. suis in human. We present this rarely-seen case in an aim to expand the clinical spectrum of S. suis infection thus help clinicians recognize that patients present with fever, headache and lower back pain may also be a S. suis infection, especially for those who have had a history of close contact with sick pigs or pork.