Was tested positive for pertussis. Is baby at risk?

Depends. If you were found to have antibodies in your blood against pertussis, you have been immunized like most people or recovered from the disease. If your cough was found to be due to pertussis, then baby, if unimmunized, may be given antibiotics prophylactically. Congratulations on being a parent -- awsome joys and awesome responsibility.
Probably!!! Generally yes. If you have a serious cough and tested psoitive in the 1st 3 weeks of the illness there is risk to the baby. Call your doctor and the pedoatrician for help. It can be deadly to infants!