Diffusion-weighted MRI abnormalities in an outbreak of Streptococcus agalactiae Serotype III, multilocus sequence type 283 meningitis

Abstract

Purpose: In 2015, an outbreak of group B streptococcal (GBS) infection caused by Streptococcus agalactiae Serotype III, multilocus sequence type 283, related to consuming infected raw freshwater fish, affected more than 200 patients in Singapore. We describe the clinical, laboratory, and neuroimaging features of a subgroup of adults with central nervous system (CNS) infections caused by GBS.

Materials and methods: The database of the Singapore Neurologic Infections Program (SNIP), a national multicenter study for surveillance of infectious neurologic disease, was reviewed to select patients with GBS CNS infection during the outbreak. Cases were diagnosed on the basis of clinical features, cerebrospinal fluid (CSF) findings and identification or isolation of Streptococcus agalactiae in the blood or CSF. Demographic, clinical and neuroradiological information was obtained prospectively and retrospectively abstracted.

Results: Fourteen patients (6 male, 8 female; median age, 58 years) presented with fever, meningism, headache, encephalopathy, focal neurological deficits, and/or seizures. All except two were previously healthy. Diffusion-weighted imaging (DWI) on admission was abnormal in 13 patients, showing tiny hyperintensities in the subarachnoid space (7 patients), ventricles (6 patients) and brain parenchyma (8 patients); 5 patients had cerebellar abnormalities.

Conclusion: Among healthy non-pregnant adults infected with Serotype III, multilocus sequence type 283 GBS meningitis linked to eating infected raw freshwater fish, DWI detected small pus collections and unusual cerebellar involvement. A collaborative national surveillance system that includes MRI can be helpful during unusual food-borne zoonotic infectious disease outbreaks.

Level of evidence: 4 J. Magn. Reson. Imaging 2017;45:507-514.

Keywords: Group B Streptococcus; Streptococcus agalactiae; meningitis; outbreak; stroke.

Figure 1

Case 6 GBS meningitis. Tiny discrete focal hyperintense abnormalities (arrows) are seen only on DWI in the posterior right interhemispheric fissure (a) and lateral ventricles (b).

Figure 2

Case 10 GBS meningitis. Multiple tiny hyperintensities are seen in the subarachnoid space in the left temporal and bilateral frontal regions (a, arrows) on DWI. Larger abnormalities are seen in the posterior limb internal capsule (b) and cerebellar vermis (c, arrowheads), with reduced ADC (d, arrowhead). The cerebellar lesion is not visible on conventional contrast‐enhanced MRI (e).

Figure 3

Case 14 GBS meningitis. A tiny hyperintensity is detected on DWI in the cerebellar vermis (a, arrowhead) and on FLAIR image (b). FLAIR images also detected additional abnormalities in the basal ganglia bilaterally and the adjacent genu of the corpus callosum (c), which were not seen on DWI. Focal moderate cerebellar enhancement on a background of mild generalized enhancement was noted after contrast injection (d, arrow).