Answer
0.1345, not unlikely.
Work Step by Step
The probability can be counted by subtracting the value of nobody having the virus from 1. Hence $P(X>0)=1-{24 \choose 0} \cdot 0.006^{0} \cdot 0.994^{24}=0.1345$. This probability is not very small, therefore the test being positive is not unlikely.
