The fourth type of performance indicator focuses on laboratory performance, and is most applicable to surveillance systems for infectious and chronic diseases, exposures to toxins, and other health conditions for which laboratory analysis and reporting of results from specimens constitute a significant part of the surveillance system. Timely reporting of laboratory results helps ensure that a source of infection or a cause of disease or disability is rapidly identified and thoroughly investigated within a community so that appropriate public health action to control or prevent it can be taken in a timely fashion. In the case of AFP and measles surveillance, performance indicators are focused on timely reporting of laboratory results, and in the case of AFP, viral isolation rates.