Eyeworld

EW RESIDENTS 94 February 2015 T he prevalence of oxacillin- and multidrug-resistant bacteria in normal conjunc- tival flora is increasing. 1,2 This is clinically important because the normal periocular flora has been established as the prevail- ing source of postoperative endoph- thalmitis. 3 During cataract surgery, gram-positive organisms gain access to the anterior chamber in 22% of cases based on aqueous cultures taken at the time of wound closure. 4 Therefore, accurately understand- ing the conjunctival flora and risk factors for antibiotic resistance can possibly guide clinical practice in the prevention of endophthalmitis. Though the risk factors for blood culture positive oxacillin-resistant coagulase negative Staphylococcus and Staphylococcus aureus have been studied extensively, little is known about the risk factors for antibiotic resistant colonization of the ocular surface. Hsu and colleagues report the risk factors associated with oxa- cillin resistance in bacteria isolated from the conjunctiva in patients prior to cataract surgery. 1 In this study, 183 subjects were given a questionnaire asking about potential risk factors for oxacillin re- sistance based on information from the general medicine and infectious disease literature, including age, gender, race, recent antibiotic use, recent hospitalization, and exposure to a healthcare facility. The only risk factor significantly associated with increased risk of oxacillin-resistant organisms in Hsu's study was recent The growing threat of MRSA looms large for all ophthalmic surgeons. This month I invited the Bascom Palmer residents to review a paper from the February JCRS that analyzes potential identifiable risk factors for patients harboring oxacillin-resistant organisms. –David F. Chang, MD, chief medical editor Review of "Assessment of risk factors for patients undergoing cataract surgery" by Nikisha A. Kothari, MD, Sarah P. Read, MD, PhD, Eric D. Hansen, MD, and Basil K. Williams Jr., MD Assessment of risk factors for oxacillin- resistant ocular flora in patients undergoing cataract surgery Hugo Y. Hsu, MD, John T. Lind, MD, Darlene Miller, DHSc, MPH, Lili Tseng, MD J Cataract Refract Surg (Feb.) 2015;41:387–392 Purpose: To assess the risk factors for harboring oxacillin-resistant Staphylococcus species on the ocular surface of patients undergoing cataract surgery. Setting: Ambulatory surgical center of Saint Louis University in Saint Louis, Mo. Design: Prospective, in vitro laboratory investigation of a patient cohort. Methods: Conjunctival cultures were obtained from patients undergoing cataract surgery on the day of surgery. Patients also answered a questionnaire about risk factors that might lead to having oxacillin-resistant Staphylococcus organisms. The risk factors tested were: 1) age, 2) gender, 3) race, 4) recent antibiotic usage, 5) recent hospitalization, and 6) exposure to healthcare or institutional settings. Logistic regression analysis was performed. Results: 183 eyes were cultured. 128 eyes revealed Staphylococcus organisms of which 70 eyes (54.7%) had oxacillin-resistant organisms. Only prior antibiotic usage—systemic and topical—was significantly associated with having oxacillin-resistant organisms (OR 8.2; 95% CI 2.2–30.5; p=0.002). The rest of the risk factors were not significantly associated: age (p=0.06), gender (p=0.33), race (p=0.34), hospitalization (p=0.94), and exposure to institutional settings (p=0.10). Conclusions: While the non-ophthalmic literature has put forth various risk factors for patients harboring oxacillin-resistant organisms, in our cohort of patients undergoing cataract surgery, only antibiotic usage in the 30 days prior to surgery was significantly associated with colonization of oxacillin-resistant organisms on the ocular surface. This finding is of importance to ophthalmic surgeons when considering perioperative antibiotic prophylaxis. Financial disclosure: The authors have no proprietary or commercial interest(s) in methods or materials discussed in this article. Steven Gedde, MD, professor of ophthalmology and vice chairman of education, Bascom Palmer Eye Institute As a clinician, risk stratification of patients is an important consideration, and this study adds meaningful data to the conversation. However, modification of current practice with the evidence presented in this study may not yet be warranted. systemic antibiotic use. A total of 24 patients reported recent antibiotic use, but 5 were excluded for topi- cal ophthalmic use. Among the 19 patients who reported systemic an- tibiotic use within 30 days prior to obtaining cultures, 7 patients were found to have oxacillin-resistant bacterial growth on cultures. Though the authors' question- naire inquires about the name of the antibiotic, the study fails to account for the complexities of antimicro- bial management, as neither the indication for use nor the class of antibiotic are well vetted. Only 6 of 24 patients were able to recall the name of the antibiotic. If a larger study were conducted, both of these variables should be included for more complete analysis. The current standard approach to prevent endophthalmitis is post- operative administration of a topical fourth-generation fluoroquinolone. Multiple studies have also shown reduced rates of endophthalmitis following administration of intraca- meral cefuroxime. 5-8 Cephalosporins are, by definition, not effective in treating oxacillin-resistant organisms in vitro using minimal inhibitory concentrations based on systemic levels. However, the authors appro- priately acknowledge that topical and intracameral antibiotics are presumed to achieve higher ocular levels than systemic administra- tion. In vitro susceptibility data may not be entirely applicable to the ophthalmic setting and patient outcomes. The results highlight that a properly powered in vivo study with endophthalmitis as a primary endpoint is warranted to guide clini- cal management. Hsu and associates previously noted that 64.9% of ox- acillin-resistant coagulase negative Staphylococcus are resistant to cipro- floxacin in vitro. 9 In support of this data, one study found that less than 50% of cases with methicillin-resis- tant endophthalmitis are sensitive to fourth-generation fluoroquinolo- nes. 10 Given the standard use of fluo- roquinolones, investigating the rate of bacterial resistance to this class of antibiotics might be more relevant clinically. This would require a larger sample size due to lower rates of resistance. Additionally, the ocular biome and antibiotic resistance vary geographically, 1 which is important to consider when determining the EyeWorld journal club

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