To investigate potential seasonality in incidence of Anti-GQ1b syndrome (AGS).

Guillain-Barré syndrome (GBS) is known to have seasonality in occurrence. However, such an epidemiological trend has not been described in AGS, a variant of GBS.

A population-based retrospective study was designed. Study period covered 2013-2018. AGS was defined by positive serum Anti-GQ1b IgG antibody. Antibody assay was performed by a single accredited laboratory by ELISA. GBS was identified by ICD9 diagnostic coding. Monthly incidence of positive Campylobacter jejuni (CJ) stool culture was also obtained for comparison. Clinical data were retrieved from the common database of the public hospital system covering 90% of local hospital service with a population of 7.5million. Poisson regression or negative binomial model with long-term time trend and harmonic terms were used to characterise the seasonal pattern of the incidences. The seasonal pattern was tested using the likelihood ratio test. AIC was used to select the best model.

A total 237 cases of AGS, 572 cases of GBS and 2,434 positive stool cultures were identified. The annual incident rate was 0.54 and 1.30 per 100,000 of AGS and GBS respectively. Male predominance was noted in both conditions. Poisson regression was selected for for AGS and GBS, and negative binomial model was selected for CJ infection. Clear significant seasonal pattern was identified for all three syndromes/ infections (likelihood ratio test, all p < 0.001 for the seasonal terms). The peak months were estimated to be around March to April for AGS and CJ infections, and February to March for GBS.

We described the population epidemiological data including the incidence of AGS and seasonal variability. Early spring was found to be the peak season for AGS occurrence. It is concordant to the seasonal peak of CJ infection, and overlaps with that of GBS.