Incidence of Guillain–Barré syndrome during Zika virus outbreak

Dear Editor:

We read with great interest the article “Incidence of Guillain–Barré syndrome (GBS) at a secondary centre during the 2016 Zika outbreak.”¹ Del Cario Orantes et al. conclude that “cases of Guillain–Barré syndrome increased during the Zika outbreak, with increases in incidence and the number of cases per month; however, no direct causal relationship could be established between these 2 conditions.”¹ We would like to share some ideas and experiences on this subject. Firstly, the increased incidence of GBS may or may not be related to Zika virus infection. Several possible concurrent problems, such as other infections or vaccination during the study period, may give rise to increased incidence. In our setting in tropical Asia, where Zika virus is also endemic, increased incidence of GBS has not been observed.² Most cases of Zika virus infection in our setting are asymptomatic and present no complications.³ Considering that Zika virus infection may be asymptomatic, the exact calculation of GBS incidence is difficult, and diagnosis of Zika virus infection related to GBS is problematic in any situation.⁴