Final answer:
The roommate of someone with bacterial meningitis should receive prophylactic antibiotics to reduce the risk of infection, and diagnosis typically involves lab testing of CSF or blood.
Step-by-step explanation:
The roommate of a college student with bacterial meningitis and a petechial rash is at risk of exposure to N. meningitidis, a pathogen that can lead to meningococcal disease. The presence of a petechial rash is particularly characteristic of meningococcal meningitis. For diagnostic confirmation, laboratory testing of the cerebrospinal fluid (CSF) or blood to detect the causative bacteria is done using techniques such as culture, antigen detection, or polymerase chain reaction (PCR). The roommate should receive prophylactic antibiotics, such as rifampin, ciprofloxacin, or ceftriaxone, to minimize the risk of developing the disease.