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

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.

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.

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.

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'.

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.