Enhanced surveillance for measles in low-incidence territories of the Russian Federation: defining a rate for suspected case investigation.

The rate of case investigation for measles-like illness (MLI) is an important indicator for the quality of measles surveillance in countries targeting measles elimination. However, a benchmark rate is still being discussed. We assessed different rates of investigation in 11 territories of the Russian Federation with low reported measles incidence during the previous 4―7 years. Each territory maintained their existing surveillance activities and also undertook additional surveillance activities for MLI over a 3-year period. The annual routine rate of investigation varied from 0·06 to 1·8/100 000 population; the overall rate of investigation, including enhanced surveillance, varied from 1·4 to 7·2/100 000. Forty-nine (30·8%) of 159 measles cases detected were identified through enhanced surveillance. Based on the results of this study, the Russian Federation concluded that a rate of routine investigation of 2/100000 provided the best balance between available resources and sensitivity for detection of measles cases.