A statistical approach to an outbreak of endophthalmitis following cataract surgery at a hospital in the West of Scotland

All India Ophthalmological Society (AIOS) Task Force guidelines to prevent intraocular infections and cluster outbreaks after cataract surgery

Infectious endophthalmitis is a serious and vision-threatening complication of commonly performed intraocular surgeries such as cataract surgery. The occurrence of endophthalmitis can result in severe damage to the uveal and other ocular tissues even among patients undergoing an uncomplicated surgical procedure. If the infections result from common factors such as surgical supplies, operative or operation theater-related risks, there can be a cluster outbreak of toxic anterior segment syndrome (TASS) or infectious endophthalmitis, leading to several patients having an undesirable outcome. Since prevention of intraocular infections is of paramount importance to ophthalmic surgeons, the All India Ophthalmological Society (AIOS) has taken the lead in the formation of a National Task Force to help ophthalmic surgeons apply certain universal precautions in their clinical practice. The Task Force has prepared a handy checklist and evidence-based guidelines to minimize the risk of infectious endophthalmitis following cataract surgery.

Application of Hazard Analysis Critical Control Points to control surgical site infections in hip and knee arthroplasty

This study examined critical points linked to the increase of surgical site infections in patients undergoing joint replacement. With this type of infection, it is not always possible to detect specific causes, and it often is necessary to perform a systematic review of assistance processes. Using Hazard Analysis Critical Control Points methodology, 4 stages of patients' pathway were identified: preoperative assessment, surgical procedure, postoperative assistance, and discharge. Surgical site infection risk factors were identified for each stage and categorized as patient conditions, staff and procedures, equipment, and environment.

Prophylaxis of postoperative endophthalmitis following cataract surgery: results of the ESCRS multicenter study and identification of risk factors

PURPOSE

To identify risk factors and describe the effects of antibiotic prophylaxis on the incidence of postoperative endophthalmitis after cataract surgery based on analysis of the findings of the European Society of Cataract & Refractive Surgeons (ESCRS) multicenter study.

SETTING

Twenty-four ophthalmology units in Austria, Belgium, Germany, Italy, Poland, Portugal, Spain, Turkey, and the United Kingdom.

METHODS

A prospective randomized partially masked multicenter cataract surgery study recruited 16 603 patients. The study was based on a 2 x 2 factorial design, with intracameral cefuroxime and topical perioperative levofloxacin factors resulting in 4 treatment groups. The comparison of case and non-case data was performed using multivariable logistic regression analyses. Odds ratios (ORs) associated with treatment effects and other risk factors were estimated.

RESULTS

Twenty-nine patients presented with endophthalmitis, of whom 20 were classified as having proven infective endophthalmitis. The absence of an intracameral cefuroxime prophylactic regimen at 1 mg in 0.1 mL normal saline was associated with a 4.92-fold increase (95% confidence interval [CI], 1.87-12.9) in the risk for total postoperative endophthalmitis. In addition, the use of clear corneal incisions (CCIs) compared to scleral tunnels was associated with a 5.88-fold increase (95% CI, 1.34-25.9) in risk and the use of silicone intraocular lens (IOL) optic material compared to acrylic with a 3.13-fold increase (95% CI, 1.47-6.67). The presence of surgical complications increased the risk for total endophthalmitis 4.95-fold (95% CI, 1.68-14.6), and more experienced surgeons were more likely to be associated with endophthalmitis cases. When considering only proven infective endophthalmitis cases, the absence of cefuroxime and the use of silicone IOL optic material were significantly associated with an increased risk, and there was evidence that men were more predisposed to infection (OR, 2.70; 95% CI, 1.07-6.8).

CONCLUSIONS

Use of intracameral cefuroxime at the end of surgery reduced the occurrence of postoperative endophthalmitis. Additional risk factors associated with endophthalmitis after cataract surgery included CCIs and the use of silicone IOLs.

Reducing the risk for endophthalmitis after cataract surgery: Population-based nested case-control study

PURPOSE

To characterize operative and nonoperative risks for the potentially blinding complication of endophthalmitis after cataract surgery.

SETTING

Ophthalmology services for the whole state of Western Australia.

METHODS

This retrospective population-based nested case-control study in Western Australia covered the period between 1980 and 2000. For each of the 205 cases of endophthalmitis, 4 time-matched controls were randomly selected from all cataract operations performed in the state. Conditional logistic regression was used to estimate multivariate adjusted odds ratios (ORs) and 95% confidence intervals (CIs) for the risk factors of interest.

RESULTS

Wound location, suturing the wound, and type of cataract operation did not affect the risk for postoperative endophthalmitis. Antibiotic prophylaxis reduced the risk, but only if given as a subconjunctival injection (OR, 0.46; 95% CI, 0.29-0.70). The risk for endophthalmitis was greater with same-day surgery (OR, 2.27; 95% CI, 1.52-3.41) than with admission the day before surgery. A concurrent eyelid procedure was a substantial risk. Surgeons within 2 years of obtaining specialist qualifications were more likely to have a case of endophthalmitis, although this was partly the result of more posterior capsule breaches. Posterior capsule breach increased the risk when it occurred in private hospitals (OR, 13.57; 95% CI, 4.00-45.99), but not in public hospitals.

CONCLUSIONS

Nonoperative as well as operative factors are important in the prevention of endophthalmitis. Subconjunctival injection of antibiotics appears to be beneficial for endophthalmitis prophylaxis. The model showed that active risk management strategies designed to optimize hospitalization and chemoprophylaxis may reduce the incidence of endophthalmitis by up to 81%.

A cluster of deep bacterial infections following eye surgery associated with construction dust

SUMMARY

Three cases of serious eye infection (two endophthalmitis, one orbital cellulitis; two caused by Staphylococcus aureus, one caused by viridans streptococci) occurred shortly after surgery (two cataracts, one retinal detachment repair) within two weeks. There had been construction work adjacent to the theatres during this time, and fine dust was found on horizontal surfaces. Further surgery was cancelled, the construction work was completed and theatres were cleaned before recommencing with no further infections. Following a review of factors that may be involved in the pathogenesis of endophthalmitis, it is proposed that the mechanism of infection in these cases may have been due to the presence of foreign material enhancing the pathogenicity of the small numbers of organisms often found in intra-ocular fluids during surgery. This hypothesis could be tested in experimental models of endophthalmitis.

Monte–Carlo simulation of random clustering of endophthalmitis following cataract surgery

BACKGROUND

Endophthalmitis remains a serious and potentially blinding complication of cataract surgery with an overall incidence of approximately 0.14% or one in 700 operations. Despite this knowledge of overall frequency, healthcare providers find themselves confronted with clusters of cases where the appropriate level of response to the cluster is uncertain.

AIM

To illustrate, by means of Monte-Carlo simulation models, the likelihood of random clustering of cases arising in units within a healthcare setting resembling the NHS and separately within the practices of individual surgeons.

METHOD

Simulation models were constructed within a programming language in which individual cataract operations were simulated with a one in 700 likelihood of each operation resulting in a 'case of endophthalmitis'. Random clustering of 'cases of endophthalmitis' was observed in the models and 'outbreaks' were noted and tracked for various outbreak definitions.

RESULTS

The model outputs are presented graphically as the proportion of 'simulated units' affected by an 'outbreak' in a year and separately as the proportion of surgeons affected for a range of 'outbreak definitions'.

CONCLUSION

These data presentations are easy to use and should facilitate a better understanding of shifts from endemic to epidemic rates of endophthalmitis with appropriate investigation of situations where a remediable common cause may exist.

Association of hospital and surgeon operation volume with the incidence of postoperative endophthalmitis: Taiwan experience

PURPOSE

To determine the association between hospital and surgeon volume with the incidence of postoperative endophthalmitis.

METHODS

A prospective cohort study was conducted to analyse the national health insurance claims data of those patients receiving cataract surgery in 2000 in Taiwan. A total of 108,705 patients who received cataract surgery by 1004 surgeons at 494 hospitals were followed to the end of 2002. Stepwise Cox regression was used to analyse the effects of hospital and surgeon volume of cataract surgery on postoperative endophthalmitis after adjustment for patient's age, gender, education, ophthalmic comorbidities, general comorbidities, and surgical factors including operative methods, different types of intraocular lenses, and surgeon's age.

RESULTS

The 2-year incidence of postoperative endophthalmitis at high-volume hospitals (0.90%) was lower than low-volume hospitals (1.16%). The incidence of postoperative endophthalmitis by high-volume surgeons (0.59%) was lower than those by middle-high-volume (0.73%), middle-low-volume (0.80%), or low-volume surgeons (1.16%). After controlling for case mix, the risk of postoperative endophthalmitis of the low-volume hospitals (hazard ratio (HR) = 1.39) was higher than that of the high-volume hospitals. The risk of postoperative endophthalmitis of low-volume surgeons (HR = 1.67) was higher than that of the high-volume surgeons.

CONCLUSIONS

The provider volume (hospital and surgeon volume) is associated with the risk of postoperative endophthalmitis. The patients who receive cataract surgery at low-volume hospitals or by low-volume surgeons have significantly higher risk of postoperative endophthalmitis than at high-volume hospitals or by high-volume surgeons. Provider volume can be considered in further postoperative endophthalmitis study as a risk factor.

Influence of age on conjunctival bacteria of patients undergoing cataract surgery

AIM

To ascertain the effect of elderly in the conjunctival bacteria frequency of patients undergoing cataract extraction.

METHODS

A retrospective case series study of 4432 consecutive patients who underwent cataract surgery, without excluding any of them for having pre-existing diseases. Their preoperative conjunctival culture were performed over a 3-year period (1994-1996). Bacteria were grouped in nine categories and patients were divided into seven groups, according to age; comparisons between groups were made by means of the chi(2) test, and the Mantel-Haenszel test to analyse age as a confounder, using SPSS program, version 12.

RESULTS

Patients aged over 74 years accounted for 41.4%; women predominated among this group (61.4%), but not in the patients younger than 75 (47.7%); In the whole sample women accounted for 53.4%. Patients aged 75-96 years had a greater frequency of: Corynebacteria, Staphylococcus aureus, Streptococcus sp. (except Streptococcus pneumoniae), Gram-negative cocci and Gram-negative rods (except Haemophilus sp.) and 'other bacteria' categories than those aged 3-74 years. Different bacteria frequency in both sexes produced a confounding effect in the comparison between age-groups. Men had more Staphylococci coagulase (-), S. pneumoniae and Gram-negative rods than women.

CONCLUSIONS

Elderly patients awaiting cataract surgery had more conjunctival bacteria than those younger than 75 years, except Staphylococcus coagulase negative, S. pneumoniae and Haemophilus sp. At any age, men had more bacteria than women. These increments of frequencies could increase the risk of intraocular surgery contamination.

A model for the management of an atypical endophthalmitis outbreak

PURPOSE OF STUDY

To present a model for the assessment, investigation, and management of an atypical outbreak of infectious endophthalmitis of indeterminate aetiology.

METHODS

A published statistical model was used to determine when the case-load constituted an outbreak. Intraocular surgery was discontinued and a multidisciplinary infection control team was formed aimed at identifying potential causative factors among the following categories: environment around theatre, preoperative preparation, intraoperative theatre practices, intraoperative surgical practices, postoperative practices, equipment maintenance guidelines, cleaning/sterilization practices, and microbiological screening.

RESULTS

Five cases of postoperative endophthalmitis developed following uncomplicated phacoemulsification cataract surgery by different surgeons over a 7-month period. Despite full investigation no single focus of infection could be determined. Four out of five cases were culture positive. Three grew Streptococcus viridans of different strains. The fourth culture grew Staphylococcus aureus. In the absence of a single causative factor, it was postulated the combined effect of multiple potential factors may have led to an increased bacterial load and subsequent infection rate. Improved practices were initiated including new cleaning protocols to combat the build-up of debris on phacoemulsification instruments. Cataract surgery was resumed with 3-monthly microbiological monitoring. There have been no further cases in the 12 months following the changes.

CONCLUSION

Outbreaks of endophthalmitis typically present over a short time period and could often be attributed to a single infective cause. We present our experience of detecting and managing this cluster and recommend a 'ground-up' multidisciplinary model to manage future outbreaks of this devastating condition.

Investigation into postoperative endophthalmitis and lessons learned

PURPOSE

To describe an approach to the investigation of a series of endophthalmitis cases to determine whether there was a true outbreak.

SETTING

Outpatient facility, Sunderland, England.

METHODS

Different approaches to statistical analysis of the probability of infrequent events being due to chance occurrence are described. Potential factors leading to an outbreak were reviewed.

RESULTS

Bayesian statistical analysis was shown to be appropriate in the determination of an endophthalmitis outbreak. The only factor found to account for the outbreak was the operating surgeon's recent abandonment of subconjunctival antibiotic prophylaxis. This decision was based on the absence of good evidence that subconjunctival antibiotic injection is effective in prophylaxis. These endophthalmitis cases demonstrate that the absence of evidence for effect is not the same as there being no effect.

CONCLUSIONS

Bayesian statistical analysis has a place in determining whether an outbreak has occurred. Withdrawing treatment simply on the basis of a lack of good evidence can lead to undesirable outcomes.

Climatic influence on conjunctival bacteria of patients undergoing cataract surgery

PURPOSE

To describe the monthly prevalence of conjunctival bacteria in patients undergoing cataract extraction and the possible climatic influence on it, in Madrid, in order to clarify postsurgical endophthalmitis pathogenesis.

METHODS

The lower conjunctival content sample of 4432 consecutive patients awaiting cataract surgery was cultured from January 1994 to December 1996. The dates of the operations and the rehospitalization for postsurgical endophthalmitis, if this took place, were checked. The isolated bacteria were grouped to study the statistical significance of the differences in the monthly prevalence differences (chi2 tests). Temperature and relative humidity are given monthly for the area where our patients live.

RESULTS

The total frequency of the conjunctival bacteria increases in April, May, and June, when the daily average temperature rises from 12 to 22 degrees C and the relative humidity oscillates between 45 and 60% in our area. Bacteria groups' frequency was significantly higher as follows: Staphylococci coagulase negative ( > 60%) in April, May, and June; Corynebacterium sp ( > 33%), Staphylococcus Aureus ( > 8%), and other Gram-positive bacteria ( > 2.5%) in May; Streptococcus Pneumoniae increases ( > 3.4%) in March, November, and December; Haemophilus sp ( > 3.4%) in January and April; Gram-negative Cocci ( > 3%) in April; and other Streptococcus sp ( > 6%) in April, May, and September. Our incidence of rehospitalization for endophthalmitis after cataract extraction in May and June together was 3.37 times higher than in the other months.

CONCLUSION

Conjunctival bacteria of our patients undergoing cataract surgery present a seasonal prevalence pattern, which could be considered as a predisposing condition for having postsurgical endophthalmitis in certain months.

Residual debris as a potential cause of postphacoemulsification endophthalmitis

AIM

To examine residual debris within sterilised instruments prior to cataract surgery.

METHODS

(i) Flushings from 32 sets of phacoemulsification instruments, sterilised according to hospital routine protocols, were taken preoperatively and analysed by scanning electron microscopy (SEM). (ii) A total of 16 sets of flushings from a different institute were collected-with separation of samples collected from phacoemulsification and those from irrigation-aspiration (IA) instruments-and analysed in the same way. (iii) A total of 15 sets of flushings were collected from instruments where an automated flushing system was used prior to sterilisation.

RESULTS

(i)In the first study, 62% were clean, 16% were moderately contaminated and 22% were severely contaminated. Various contaminants were identified including lens capsule and cells, man-made fibres, squamous cells, bacteria, fungal elements, diatoms, red blood cells and proteinaceous material. (ii) In the second study, the results were similar and contamination of both phacoemulsification and IA instruments was shown. (iii) The third study showed that although a decrease in contamination followed automated flushing, contamination was not completely eliminated.

CONCLUSIONS

Although all equipment had been sterilised, pyrogenic material was still present. These findings emphasise the importance of meticulous cleaning of all surgical equipment in which biological debris can remain.