In seven countries that recently experienced Zika outbreaks, there were also sharp increases in the numbers of people suffering from a form of temporary paralysis, researchers reported Wednesday.

The analysis, published online in The New England Journal of Medicine, adds to substantial evidence that Zika infections — even asymptomatic ones — may bring on a paralysis called Guillain-Barré syndrome.

The syndrome can be caused by a number of other factors, including infection with other viruses. Researchers studying the Zika epidemic in French Polynesia had estimated that roughly 1 in 4,000 people infected with the virus could develop the syndrome.

The Centers for Disease Control and Prevention has said that the Zika virus is “strongly associated” with Guillain-Barré, but has stopped short of declaring it a cause of the condition.