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Microbiological Surveillance of Operation Theatre

Geeta Mehta, Professor and Head, Dept of Microbiology, Lady Hardinge Medical College, New Delhi.

Controversy exists over the extent and frequency of microbiological surveillance of operation theatres. Sources of exogenous infection in the operation theatre could be the air and the environment of the theatre including equipment and articles coming in direct contact with the wound or other vulnerable areas of the patient. Modern operation theatres must fulfil standards of design and ventilation. Bacterial contamination of the air should be within acceptable limits. Standard cleaning, disinfection and sterilisation procedures; good theatre practice and discipline can provide a microbiologically safe environment in the theatre. Based on scientific principles a protocol for surveillance is suggested.

INTRODUCTION
In the operation theatre the sources of infection may be either endogenous (from the patient himself) or exogenous from the theatre environment. Although most surgical wound infections originate from the patient's own microflora,4 exogenous sources are also implicated.
A large body of information is available which indicates that prevention of post operative infection is dependent on several factors including effective sterilisation and disinfection procedures, good surgical technique, theatre design, bacterial contamination of theatre air, discipline which includes restricting the movement of staff near the operating table, appropriate use of prophylactic antibiotics etc. [5] , [17]

AIR AS A SOURCE OF INFECTION
Air borne contamination is mainly derived from the personnel in the operation theatre and their activities. The bacterial count in operation theatre is influenced by the number of individuals present, ventilation and air flow. [4] Exogenous infections of surgical wounds are caused predominantly by Staphylococcus aureus and S. epidermidis is an important pathogen in implant surgery. S. aureus and S. epidermidis are shed into the environment in skin scales of which 106 are shed by an individual each day. Healthy carriers shed few staphylococci. Most outbreaks are caused by heavy dispersers. [4] , [20] Studies in a number of operating theatres have suggested that there is a general relationship between total air count and risk of infection. Counts in the range of 700-1800/m 3 were related to significant risk of infection and when they were under 180/m 3 the risk was slight. [20]
Proper design and ventilation of operation theatres is the most important means of controlling air borne contamination and thus preventing air borne infection in operation theatre. The theatre should be seggregated into zones : aseptic, clean, less clean and have mechanical ventilation. [3] Failure to provide adequate operation theatre ventilation associated with risk of postoperative infection has been described. [11] Theatre ventilation has been found to be a critical factor in prosthetic and joint surgery. In a multicentric study of hip and knee operations, incidence of sepsis in operations performed under laminar air flow was significantly lower than in operations performed under conventional ventilation. [17] In our own study in a neurosurgical operation theatre similar findings were observed. [19]
Recommended ventilation standards for operation theatre are that the theatre should have artificial ventilation of the plenum type which can provide approximately 20 air changes per hour. [14] Laminar air flow has been recommended for prosthetic implant surgery. [4] , [14] Laminar flow may provide over 400 air changes per hour.
Standards for air borne contamination [9] , [10] Conventional ventilation of plenum type



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