2001 Matthew J. Arduino, DRPH Under a very high magnification of 50,000x, this scanning electron micrograph (SEM) shows a strain of Staphylococcus aureus bacteria taken from a vancomycin intermediate resistant culture (VISA).Under SEM, one can not tell the difference between bacteria that are susceptible, or multidrug resistant, but with TEM, at least with VISA isolates one can see a thickening in the cell wall that may attribute to their reduced susceptibility to vancomycin . See PHIL 11158 for a black and white version of this image. VISA and VRSA are specific types of antimicrobial-resistant staph bacteria. While most staph bacteria are susceptible to the antimicrobial agent vancomycin some have developed resistance. VISA and VRSA cannot be successfully treated with vancomycin because these organisms are no longer susceptibile to vancomycin. However, to date, all VISA and VRSA isolates have been susceptible to other Food and Drug Administration (FDA) approved drugs. How do VISA and VRSA get their names?Staph bacteria are classified as VISA or VRSA based on laboratory tests. Laboratories perform tests to determine if staph bacteria are resistant to antimicrobial agents that might be used for treatment of infections. For vancomycin and other antimicrobial agents, laboratories determine how much of the agent it requires to inhibit the growth of the organism in a test tube. The result of the test is usually expressed as a minimum inhibitory concentration (MIC) or the minimum amount of antimicrobial agent that inhibits bacterial growth in the test tube. Therefore, staph bacteria are classified as VISA if the MIC for vancomycin is 4-8µg/ml, and classified as VRSA if the vancomycin MIC is >16µg/ml.

Study from Private Hospital Chain Reveals High Mortality in Patients with Multi Drug Resistant Infections

A retrospective, observational study from a well-known chain of private hospitals, has shown that the mortality rates in patients infected with multi-drug resistant organisms (MDRO) is much higher than that in patients infected with drug susceptible strains. This result, in and of itself, is not of much interest, as it is quite self-evident, that patients who are infected with MDROs are more likely to experience a poor clinical outcome. The real importance of the findings lies in the fact that they provide a baseline estimate for occurrence of MDROs, and their drug resistant patterns, in the examined settings.

Emergence of MDROs (NIAID Flickr)

The study provides valuable insights about the impacts of AMR/MDR organisms in certain clinical settings. These results may be considered of interest, particularly as baseline estimates in the defined clinical settings, from where the AST results were obtained. Future studies can build on these findings, addressing some of the limitations imposed on it due to the chosen design. However, it needs to be kept in mind that often the circulating strains of MDROs are largely a function of the pattern and amount of antibiotics used in that particular clinical facility. Hence, the pattern of MDROs observed in private, tertiary care centers, with high volumes of patients suffering from a greater severity of clinical manifestations, is likely to be very different from the patterns observed in primary healthcare centers, generally focusing on maternal and child health issues, with limited range and intensity of antibiotic use.

Another limitation of generalizing these results for dictating health policy at a larger level is the fact that the clinical data for the patients was not incomplete. It seems that the analyses, while going into great depth while assessing the antimicrobial resistance profiles, has been limited when it comes to controlling for co-existing illnesses, primary diagnoses, severity of presentation, existence of comorbidities, risk factor profile, past medical history, and several other factors which can affect mortality rates. Thus, considering the absence of clinical data which would have helped in controlling for several factors that affect prognosis, caution should be exercised in using these results for prognostication of similar patients in other clinical settings, particularly at the primary or secondary levels, which may have a different spectrum of AMR/MDR organisms.

The study also touches upon the fact that MDROs may even be acquired at the community level. While the retrospective study design does not absolutely rule out the possibility of establishing the temporal order of acquiring MDRO infections, this probably is not the best study design to explore this research question. In order to further strengthen the contention that high rates of MDR organisms exist at the community level, and are causing clinically significant infections, more appropriate study designs (longitudinal, surveillance-based), with genetic linking of strains, could be considered.

The current study, while highlighting the situation of MDR organism-related mortality, has limited utility when it comes to designing specific interventions which may improve outcomes. The highlighted association should be of concern and should guide clinical establishments in engaging more deeply with stewardship efforts and infection prevention and control mechanisms, till evidence of other, more efficient interventions are generated.

Crucially, by proxy, one may posit that the study is a good starting point for the participating institutions in designing appropriate interventions, including antibiotic stewardship efforts, to curb the menace of the MDRO infections. The baseline has been set and now they have the ethical and methodological imperative to design interventions that can be implemented to reduce the burden of MDRO infections. Subsequent gains in mortality reduction, if demonstrable, could also be a potent advantage of this approach.


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