Health officials confirmed six new cases of whooping cough since Friday, and two are in Sacajawea Middle School.
This is the second case to be identified at another school besides Bozeman High School.
Gallatin County health officer Matt Kelley said one pertussis case in a school is not unsual, but they are working to make sure it doesn't spread to other middle school students.
Three of the cases reported over the weekend are Bozeman High students, the fifth case is a parent. Another case at Sacajawea was confirmed Tuesday.
Those new cases, combined with updated numbers, puts the total number of cases of Pertussis at 39. Almost all are linked to Bozeman High School.
Kelley said when positive cases are confirmed, those people are already on antibiotics to treat the infection.
"We're getting the test results back- those people are already on antibiotics almost all the time" he said. "What's important about that test is that then we can go out and we know that that person is positive, and we can start that case investigation all over again- we can go find their close contacts."
The pertussis outbreak started at the end of October. Some of the first cases reported involved Bozeman High's varsity football team.
To help fight the spread, health workers put 350 people on antibiotics, but Kelley said that only protects them for 10 days.
He said any kids identified as "close contacts" more than once may have to be treated again. Being a close contact means that person was exposed to the disease, by being within arms length of someone who is sick for 30 minutes or more.
Any students in the high school that have not been vaccinated have been asked not to come to school.
Bozeman Public Schools released a "Frequently Asked Questions" for parents on how to handle the outbreak. You can find that by clicking here.