How dangerous is yersinia?

Which species?: The genus Yersinia includes pestis (cause of plague), enterocolitica and pseudotuberculosis. Each can produce severe and potentially life-threatening disease if you become infected. Generally the latter two produce gastroenteritic infections and can mimic appendicitis. Infections may be followed by Guillian-Barre syndrome.

Most of time okay...: I assume you're talking about the yersinia that causes diarrhea and abd discomfort. Most cases do not merit treatment. In people with co-morbidities (diabetes, suppressed immune system) and those with severe disease (the bacteria is in the blood stream and they're septic), then it can be dangerous and treatment is needed. Most of the time cases get better on their own.

Which species?: The genus Yersinia includes pestis (cause of plague), enterocolitica and pseudotuberculosis. Each can produce severe and potentially life-threatening disease if you become infected. Generally the latter two produce gastroenteritic infections and can mimic appendicitis. Infections may be followed by Guillian-Barre syndrome.