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When to declare an endophthalmitis outbreak: Poisson model of postcataract surgery endophthalmitis outbreak
Elizabeth Y Wei1, Jim Xie, Marko M Popovic
1From the Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada (Wei); Department of Ophthalmology and Vision Sciences, University of Toronto, Toronto, Ontario, Canada (Xie, Popovic, Jin, Kertes, Schlenker, Teichman, Ahmed, Amandeep S. Rai, Amrit S. Rai); Kensington Eye Institute, University of Toronto, Toronto, Ontario, Canada (Kertes, Schlenker, Ahmed, Amandeep S. Rai, Amrit S. Rai); John and Liz Tory Eye Centre, Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada (Kertes); Prism Eye Institute, Oakville, Ontario, Canada (Schlenker, Teichman, Ahmed, Amandeep S. Rai, Amrit S. Rai); Division of Ophthalmology, Trillium Health Partners, Mississauga, Ontario, Canada (Schlenker, Teichman, Ahmed, Amandeep S. Rai, Amrit S. Rai).
Purpose:
To create an accessible, online tool that determines the likelihood of an endophthalmitis outbreak.
Setting:
Surgical centers that perform cataract surgeries.
Design:
Mathematical modelling study.
Methods:
The global risk of acute postoperative endophthalmitis (POE), defined as occurring within 6 weeks after standalone cataract surgery, was determined from a systematic review. An online tool was then created using the Poisson model to determine the likelihood of a POE outbreak. The model used the number of cataract surgeries performed, time, and the number of POE cases observed. Significance was defined as P < .05, P < .01, or P < .001.
Results:
From the 25 included studies, the mean standard risk of POE after standalone cataract surgery was 0.0692% (range: 0.0189% to 0.102%). The model demonstrated that for a center that performs 1000 cataract surgeries in a month, the probability of at least 1 POE case occurring in a month is not statistically significant ( P = .461, P > .05), and therefore, an outbreak is unlikely. By contrast, the probability of at least 3 POE cases occurring in a month at this center is statistically significant ( P < .05), and thus, has moderate evidence for an outbreak with 95% confidence.
Conclusions:
The Poisson model represents an evidence-based way to determine whether the number of POE cases is within expectations for the number of cataract operations performed over a period. This online tool provides ophthalmologists and public health agencies with helpful data to guide POE outbreak declaration decisions.
