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Investigation of postoperative endophthalmitis
LETTERS
DAVID T.L. LIU, MRCS VINCENT Y.W. LEE, FRCS WAI-MAN CHAN, FRCP, FRCS DENNIS S.C. LAM, MD, FRCOPHTH Hong Kong, China
IOP-lowering effects and late complication rates of both procedures in the 3-year period.dIlgaz Sagdic Yalvac, MD
Investigation of postoperative endophthalmitis In their investigation of postoperative endophthalmitis outbreaks,1 Mandal and coauthors conclude that the withdrawal of prophylactic subconjunctival antibiotic injection was solely responsible for the outbreaks. However, we have a different point of view and believe in the presence of an alternative factor. In the meta-analysis of bacterial prophylaxis for cataract surgery by Ciulla and coauthors,2 preoperative povidone–iodine (PVI) received the highest clinical recommendation level B and the greatest strength of supporting evidence rating II, which are higher than those of prophylactic antibiotics. In their investigation, Mandal and coauthors overlooked the role of preoperative cul-de-sac disinfection by PVI 5%, especially the importance of an effective instillation against exogenous endophthalmitis. If the surgeon uses several drops of PVI 5% instead of the usual continuous dripping and irrigation of the ocular surface, the disinfection efficacy is bound to be undermined. This is because irrigation by PVI is more bactericidal; a lower reservoir of iodine molecules within a small quantity of PVI is expected to be dissipated easily by the initial high bacterial load.3 A larger amount of PVI 5%, eg, 2.0 mL, may replenish the depot with the sufficient amount of available iodine against ocular surface flora.3 Furthermore, routine and undue shortening of the actual contact time of PVI with the conjunctival cul-de-sac may weaken its overall bactericidal effect. The clinically recommended contact time ranges from 3 to 5 minutes.3–5 If these nonrecommended practices, ie, scarcity of the amount of PVI and/or brevity of the contact time with the ocular surface, were the routine, the overall bactericidal efficacy of the preoperative disinfection procedures among not only those with endophthalmitis but virtually all patients operated on will be significantly reduced.2 One may wonder why the outbreak occurred only after the abstinence of prophylactic subconjunctival antibiotic injection. We believe that withdrawal of subconjunctival antibiotic is merely a potentiating factor, accentuating the deceleration in the overall bactericidal efficacy and precipitating a clinically apparent infection. This may explain why there was 1 negative culture and half the remaining cases grew no definite bacterial culture in the wake of a predetermined substandard PVI antisepsis.1 Conversely, even though there was suboptimal PVI disinfection in the patients operated on, the patients were given an extra source of bactericidal drive from the end-of-surgery subconjunctival antibiotics. Under the summation of the 2 antisepsis techniques, the overall infective dose of microbes over the ocular surface might not be high enough to trigger endophthalmitis. It should be pointed out that the authors have not fully explained how the pivotal ocular surface disinfection step by PVI 5% was carried out. Any deviation from the recommended practice will inevitably jeopardize the effectiveness of the overall disinfection and increase the risk for postoperative infection. Accordingly, abandoning the prophylactic subconjunctival antibiotic injection may not be the major factor in the observed outbreaks.
REFERENCES 1. Mandal K, Hildreth A, Farrow M, Allen D. Investigation into postoperative endopthalmitis and lessons learned. J Cataract Refract Surg 2004; 30:1960–1965 2. Ciulla TA, Starr MB, Masket S. Bacterial endophthalmitis prophylaxis for cataract surgery; an evidence-based update. Ophthalmology 2002; 109:13–26 3. Ferguson AW, Scott JA, McGavigan J, et al. Comparison of 5% povidone-iodine solution against 1% povidone-iodine solution in preoperative cataract surgery antisepsis: a prospective randomized double bind study. Br J Ophthalmol 2003; 87:163–167 4. Staudenmaier C. Current views on the prevention of postoperative infectious endophthalmitis. Can J Ophthalmol 1997; 32:297–302 5. Gopinathan U, Reddy MK, Nadkarni MS, et al. Antimicrobial effect of ciprofloxacin, povidone-iodine, and gentamicin in the decontamination of human donor globes. Cornea 1998; 17:57–61
Reply:
We thank Liu and coauthors for their interest in our paper and their comments. The primary aims of the paper were to highlight how we investigated the outbreak and the statistical methods we used to determine the outbreak. A secondary aim was to caution about the common fallacy that an absence of proof of effectiveness is the same as proof of ineffectiveness. I believe we fulfilled these aims. The use of preoperative PVI 5% was common to all surgeons in the unit, and because of the way we organize the service, we know that the contact time is greater than 3 minutes in all patients. Therefore, we are confident that there was something different with my cohort, and the most likely (but not the only possible) factor was the withdrawal of subconjunctival antibiotics. The suggestion that we have been using 2 potentially only partially effective treatments (single instillation of povidone rather than repeated instillation and subconjunctival antibiotics) and that these have somehow summated to give effective prophylaxis is an intriguing one. We wonder where is the evidence for the benefit of a continuous drip of PVI as opposed to a few drops in a normal eye? One of the papers referenced by Liu and coauthors1 looks at the decontamination of donor globes and refers to the ‘‘standard’’ of immersion in antimicrobial for 3 minutes. No provenance is given for that statement. Another of the references papers2 compares PVI concentration, not duration of irrigation, and in that paper bacterial swabs were taken between 1 minute and 2 minutes, not the standard 3 minutes. It is clear there is a need for further well-controlled studies to determine the best combination of PVI strength, length of time of irrigation, and length of total contact time to achieve the lowest prevalence of bacteria in the operating field for the expected duration of a modern cataract operation.dDavid Allen, FRCOphth REFERENCES 1. Gopinathan U, Reddy MK, Nadkarni MS, et al. Antimicrobial effect of ciprofloxacin, povidone-iodine, and gentamicin in the decontamination of human donor globes. Cornea 1998; 17:57–61
J CATARACT REFRACT SURG - VOL 31, OCTOBER 2005
1853
DAVID T.L. LIU, MRCS VINCENT Y.W. LEE, FRCS WAI-MAN CHAN, FRCP, FRCS DENNIS S.C. LAM, MD, FRCOPHTH Hong Kong, China
IOP-lowering effects and late complication rates of both procedures in the 3-year period.dIlgaz Sagdic Yalvac, MD
Investigation of postoperative endophthalmitis In their investigation of postoperative endophthalmitis outbreaks,1 Mandal and coauthors conclude that the withdrawal of prophylactic subconjunctival antibiotic injection was solely responsible for the outbreaks. However, we have a different point of view and believe in the presence of an alternative factor. In the meta-analysis of bacterial prophylaxis for cataract surgery by Ciulla and coauthors,2 preoperative povidone–iodine (PVI) received the highest clinical recommendation level B and the greatest strength of supporting evidence rating II, which are higher than those of prophylactic antibiotics. In their investigation, Mandal and coauthors overlooked the role of preoperative cul-de-sac disinfection by PVI 5%, especially the importance of an effective instillation against exogenous endophthalmitis. If the surgeon uses several drops of PVI 5% instead of the usual continuous dripping and irrigation of the ocular surface, the disinfection efficacy is bound to be undermined. This is because irrigation by PVI is more bactericidal; a lower reservoir of iodine molecules within a small quantity of PVI is expected to be dissipated easily by the initial high bacterial load.3 A larger amount of PVI 5%, eg, 2.0 mL, may replenish the depot with the sufficient amount of available iodine against ocular surface flora.3 Furthermore, routine and undue shortening of the actual contact time of PVI with the conjunctival cul-de-sac may weaken its overall bactericidal effect. The clinically recommended contact time ranges from 3 to 5 minutes.3–5 If these nonrecommended practices, ie, scarcity of the amount of PVI and/or brevity of the contact time with the ocular surface, were the routine, the overall bactericidal efficacy of the preoperative disinfection procedures among not only those with endophthalmitis but virtually all patients operated on will be significantly reduced.2 One may wonder why the outbreak occurred only after the abstinence of prophylactic subconjunctival antibiotic injection. We believe that withdrawal of subconjunctival antibiotic is merely a potentiating factor, accentuating the deceleration in the overall bactericidal efficacy and precipitating a clinically apparent infection. This may explain why there was 1 negative culture and half the remaining cases grew no definite bacterial culture in the wake of a predetermined substandard PVI antisepsis.1 Conversely, even though there was suboptimal PVI disinfection in the patients operated on, the patients were given an extra source of bactericidal drive from the end-of-surgery subconjunctival antibiotics. Under the summation of the 2 antisepsis techniques, the overall infective dose of microbes over the ocular surface might not be high enough to trigger endophthalmitis. It should be pointed out that the authors have not fully explained how the pivotal ocular surface disinfection step by PVI 5% was carried out. Any deviation from the recommended practice will inevitably jeopardize the effectiveness of the overall disinfection and increase the risk for postoperative infection. Accordingly, abandoning the prophylactic subconjunctival antibiotic injection may not be the major factor in the observed outbreaks.
REFERENCES 1. Mandal K, Hildreth A, Farrow M, Allen D. Investigation into postoperative endopthalmitis and lessons learned. J Cataract Refract Surg 2004; 30:1960–1965 2. Ciulla TA, Starr MB, Masket S. Bacterial endophthalmitis prophylaxis for cataract surgery; an evidence-based update. Ophthalmology 2002; 109:13–26 3. Ferguson AW, Scott JA, McGavigan J, et al. Comparison of 5% povidone-iodine solution against 1% povidone-iodine solution in preoperative cataract surgery antisepsis: a prospective randomized double bind study. Br J Ophthalmol 2003; 87:163–167 4. Staudenmaier C. Current views on the prevention of postoperative infectious endophthalmitis. Can J Ophthalmol 1997; 32:297–302 5. Gopinathan U, Reddy MK, Nadkarni MS, et al. Antimicrobial effect of ciprofloxacin, povidone-iodine, and gentamicin in the decontamination of human donor globes. Cornea 1998; 17:57–61
Reply:
We thank Liu and coauthors for their interest in our paper and their comments. The primary aims of the paper were to highlight how we investigated the outbreak and the statistical methods we used to determine the outbreak. A secondary aim was to caution about the common fallacy that an absence of proof of effectiveness is the same as proof of ineffectiveness. I believe we fulfilled these aims. The use of preoperative PVI 5% was common to all surgeons in the unit, and because of the way we organize the service, we know that the contact time is greater than 3 minutes in all patients. Therefore, we are confident that there was something different with my cohort, and the most likely (but not the only possible) factor was the withdrawal of subconjunctival antibiotics. The suggestion that we have been using 2 potentially only partially effective treatments (single instillation of povidone rather than repeated instillation and subconjunctival antibiotics) and that these have somehow summated to give effective prophylaxis is an intriguing one. We wonder where is the evidence for the benefit of a continuous drip of PVI as opposed to a few drops in a normal eye? One of the papers referenced by Liu and coauthors1 looks at the decontamination of donor globes and refers to the ‘‘standard’’ of immersion in antimicrobial for 3 minutes. No provenance is given for that statement. Another of the references papers2 compares PVI concentration, not duration of irrigation, and in that paper bacterial swabs were taken between 1 minute and 2 minutes, not the standard 3 minutes. It is clear there is a need for further well-controlled studies to determine the best combination of PVI strength, length of time of irrigation, and length of total contact time to achieve the lowest prevalence of bacteria in the operating field for the expected duration of a modern cataract operation.dDavid Allen, FRCOphth REFERENCES 1. Gopinathan U, Reddy MK, Nadkarni MS, et al. Antimicrobial effect of ciprofloxacin, povidone-iodine, and gentamicin in the decontamination of human donor globes. Cornea 1998; 17:57–61
J CATARACT REFRACT SURG - VOL 31, OCTOBER 2005
1853