Delhi Health Minister Saurabh Bharadwaj on Friday directed hospital administrators to conduct regular audits to prevent unlawful and corrupt practices in view of the alleged "cash-for-treatment" racket busted at the central government-run Safdarjung Hospital. The CBI has arrested a senior neurosurgeon, besides a south Delhi businessman and three middlemen, in connection with the alleged racket. The agency is probing offences, including overbilling, money laundering and demand of bribe from poor people for treatment.