To effectively perform surveillance, public health agencies require access to 'timely, accurate, and complete data' (4) . Unfortunately, data quality is an issue for many clinical information systems that capture data utilized in public health surveillance processes. This study assessed the completeness of real-world ELR data from multiple provider organizations using a variety of laboratory information systems, documenting evidence that ELR data are heterogeneous in their completeness across and within information systems. In many cases, data important to public health surveillance processes are missing, indicating suboptimal ELR data quality. The study further documented evidence that a statewide or regional HIE can employ methods to mitigate ELR data deficiencies, leading to improvements in the completeness of ELR data prior to transmission to public health agencies.