Specimens should be collected before starting antibiotics to ensure accurate identification of the causative microorganism. Antibiotics administered prior to specimen collection can reduce the bacterial load, leading to false-negative cultures or altered microbial flora. This compromise in diagnostic accuracy may result in inappropriate treatment. Collecting specimens prior to antibiotic therapy allows for the isolation and sensitivity testing of pathogens, guiding targeted antimicrobial therapy and improving patient outcomes.

Reference: Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases, Mandell et al., 9th Edition.