Vancomycin Minimum Inhibitory Concentration Trend in Methicillin Resistant Staphylococcus aureus from a Tertiary Care Hospital in Central Kerala, India

Background: Methicillin resistant Staphylococcus aureus (MRSA) is an important cause of nosocomial infections. Vancomycin is one of the mainstays for the cure of MRSA infections and vancomycin MIC creep have been reported from different parts of the world. This study evaluated the trends of vancomycin MIC among the MRSA and analysed its relationship with vancomycin consumption. Methods: During the six years of this retrospective study, the MIC of Oxacillin and Vancomycin of all clinically relevant Staphylococcus aureus were retrieved from the automated Vitek-2 compact system. The consumption rate of vancomycin in our hospital as the defined daily doses (DDDs) per 1000 bed-days were collected from Pharmacy services. The data obtained were statistically analysed. Results: Out of 1,19,112 total samples processed 2.02% were found as Staphylococcus aureus among which 44.7% were MRSA. Over the study period, all the MRSA isolates were susceptible to vancomycin and there was a statistically significant increase in isolates with vancomycin MIC =1 μg/ml depicting the MIC creep phenomenon in our isolates. But a significant correlation between DDDs/1000 bed days of vancomycin and increase in MIC range could not be established. Conclusion: There is a dire need to identify the trend of vancomycin MICs in our local area to assess the existence of creep trend and warn the clinicians of these disastrous strains. Sensitization about this type of MRSA MIC creep among the primary health physician is also needed to implement the control measures and limit its spread in communities.