Vitrat is a hostile environment. Diseases and creatures are common in these swamps, but for the inhabitants it's home. By the time an individual has reached two decades of age, they'd have gone through dozens of diseases. This makes the Vitrat people hardier than most.
Swamp born. The diseases you've had to live through has given you a resilience to combat them. You have advantage on saving throws against diseases and poisons. Of Vitrat. You have advantage on any check pertaining to Vitrat culture.