Introduction
Postoperative infection remains a major cause of morbidity amongst patients undergoing surgery. Maintenance of strict a sepsis is essential if postoperative infections and their consequences are to be minimized.1
Operating room (OR) air is persistent source of postoperative infections. In the late 18th century, the surgeon Joseph Lister used carbolic spray to disinfect the OR air for reducing the mortality rate from postoperative infection.2
Postoperative infections can be caused by a contaminated surfaces, contaminated environment, unsterile equipment, infected personnel and contaminated disinfectants.2
Biological contaminants occur in the air as aerosols and may include bacteria, fungi & viruses.3 Factors which affect the contamination in air are number of persons present in theatre, type of ventilation, rate of air exchange, quality of air provided & types of organisms.4, 5, 6 Monitoring the environment by the microbiological testing of surfaces and equipment’s is useful to detect types and counts of microbial flora.7
Air contamination is usually expressed as Bacteria Carrying Particles per cubic meter (BCP/m3) or Colony Forming Units per cubic meter (CFU/m3) of air measured with an air sampler.2
Most of the contaminants are harmless saprophytes and commensals, only 0.01% of bacteria are pathogens. Common pathogens isolated in OT are Staphylococcus.aureus, Coagulase negative Staphylococcus, Pseudomona.aeuroginosa and fungus.2
Organisms isolated and their sensitivity pattern indicates the seriousness of the infection which can guide the infection control programme effectively. Microbiologic surveillance is required to know the efficiency of disinfection methods and fumigation technique.
This study was done to analyze air contamination by settle plate method and surface swab method.
Aim and Objectives
Microbiological surveillance of OT by settle plate method & surface swab method for anaerobic & aerobic infection.
To compare the utility of surface swab method & settle plate method for routine microbiological screening of OT.
To assess the trend and quality of air maintained between two subsequent fumigations.
Methods
Over a period of 12 months, environmental Bacteria Carrying Particle (BCP) load were studied weekly and surface samples monthly. Once in four month fungal growth was detected in air conditioning filters.
Surface swabs were collected and plates for settle plate were kept after before and after fumigation. high-level disinfection were used every Saturday by formaldehyde gas generated by addition of KMnO4 and 40% liquid formalin, additional fumigation were done whenever an obviously infected case was operated.
The ORs were sealed off for 24-36 hours following formaldehyde fumigation before the next surgery. Liquid ammonia solution was used to neutralize the irritant effects of formaldehyde two hours before surgery.8
Settle plate methods
Sheep blood agar plates (10cm size) after labeling with appropriate date and time were exposed with lid opened for 30 minutes at different areas like washing room, OT table (head end and foot end), OT floor, doctors room and nurse room before and after fumigation of OT.9 Plates were closed and sealed, transported to the laboratory and incubated at 37ºC for 48hrs. Growth was observed, colony forming units (CFU) were counted. The acceptable limit of CFU was calculated by using the formula based on the colony count, area of the plate exposed, and the duration of exposure and it is fixed as 10 CFU instead of 12 to certify the OT is safe for surgery.10 Approximately 180 bacteria per cubic meter of air correspond to 10 colonies settling on a plate. The operating rooms are said to carry out operative procedures only when the bacterial load is less than 180 per cubic meter/<10 colonies grow on blood agar (BA). Detection of even a single colony of S.aureus is considered a risk for infection.11
Surface swab
Surface swabs were collected from the operation table at the head end, foot end, over head lamp, the wall near the electrical switch, the floor, Anesthesia machine, washing area, Fan and Dustbin. The swabs were inoculated in Robertson’s cooked meat broth (RCMB) for 7 days at 37℃, smears from the bottles were stained with Gram’s and examined for Clostridium.tetani spores. Results were recorded.10
Swabs were collected from filters of air-conditioning units and streaked on Sabourauds’s dextrose agar without antibiotics to isolate fungi with an interval of one month. If fungi growth was observed then air conditioner filter was cleaned using chlorine dioxide (sporicidal disinfectant).10
Commercially available spore strips impregnated with spores of Bacillus.sterothermophillus were used to check the efficacy of sterilization by autoclave. After autoclave strips were removed and aseptically transferred to RCMB which was incubated at 56ºC for 5 days. Broth was examined for signs of turbidity intermittently. Efficacy of autoclave was checked once in a month.10
Table 1
Showing CFU before fumigation
Table 2
Showing the CFU after fumigation
Table 3
List of bacteriaisolated from settle plate
|
Organisms (Bacteria) |
Percentage (%) |
|
Bacillus.subtilis |
59% |
|
Pseudomonas.spp |
14% |
|
CONS |
10% |
|
Klebsiella spp |
7% |
|
E.coli |
5% |
|
Micrococci |
3% |
|
Staphylococcu. aureus |
2% |
Table 4
List of fungus isolated from AC filter
|
Organisms (Fungus) |
Percentage (%) |
|
Aspergillus |
78% |
|
Mucor |
14% |
|
Rhizopus |
6% |
|
Penicillin. |
2% |
Table 5
Showing presences of Clostridium.tetani growth before fumigation
Results
Settle plate methods
Total of 252 settle plate samples were collected from six OT, two staff room and one washing room over a period of 12 months.
Table 1 : Explains about the observed colony count before and (Table 2) after fumigations in Operation theaters.
Bacterial and fungal growth was observed in blood agar plate, bacteria’s were identified according to CLSI guidelines. In our study we isolated Organisms like Coagulase negative Staphylococcoci, Staphylococcus aureus, Micrococci, Bacillus, E.coli, Pseudomonas and Klebsiella. Growth of Mucor and Aspergillus was observed twice in settle plate.
Surface swab
Over a period of one year, we observed morphologically resembling Clostridium.tetani like organisms in the month of October, February and May by surface swab smear stained with Gram’s as shown in (Table 5).
After fumigation Clostridium.tetani growth was not observed in operation theaters.
Fungal growth observed in air conditioner filters such as Aspergillus, Mucor, Rhizopus and Penicillin.
Discussion
This study was carried out with an interest to look for the organisms and frequency of isolates in air sample and surface swabs before and after fumigation. In this present study we isolated organisms like Coagulase negative Staphylococcoci, Staphylococcus aureus, Micrococci, Bacillus subtilis, E.coli, Pseudomonas and Klebsiella from settle plate kept open in OTs and staff rooms. Bacillus subtilis is the major contaminant found in OTs, Pathogen like Pseudomonas found to be major organism and Staphylococcus found to be least isolated.
In comparison to our study, similar organisms were isolated in a study conducted by Dr. Krunal Shah et al. They observed Bacillus subtilis 55%, Pseudomonas 38%, CONS 30%, Klebsiella 25%, E.coli 10%, Stapyloccocus.aureus 8%. In addition to our study they also isolated Proteus mirabilis and Acinetobacter spp. Study conducted by Dr. E. Rajni Sabharwal et al., showed similar organisms as observed in this present study.12, 13
Conclusion
Monitoring both aerobic and anaerobic organisms in air by settle plate and surface swab method can provide a simple and cost effective way of detecting the contamination. Surface swab with RCMB culture can only yield Clostridium.tetani were as settle plate can detect aerobic pathogens as well fungus in air.
Settle plate is more useful because aerobic postoperative infections are more common than anaerobic postoperative infections. Surface swab technique is mandatory in places where civil work is undertaken and in orthopedics due to RTA (road traffic accidents) cases & trauma cases. OT which undergoes both the methods is beneficial in detecting pathogen and prevent from hospital associated infections.
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