When to declare an endophthalmitis outbreak: Poisson model of postcataract surgery endophthalmitis outbreak projections.

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.