Cryptosporidium & Giardia in Water—Key Features and Basic Principles for Monitoring & Data Analysis

Public health implications of Cryptosporidium and Giardia (C&G) in surface water depend on the characteristics of their occurrence at locations relevant to public water supplies. Recent detailed multi-location and long-term data sets have provided an accurate and complete understanding of occurrence features not previously available. Poisson statistics describe oocyst and cyst concentrations that are characteristically low with respect to the limit of detection of best available analytical methods. The IMS-IFA based analytical methods (e.g., ISO 15553, USEPA 1622/1623) provide reliable data on levels of both C&G in water. Recovery efficiency varies widely and must be measured to give concentration data that can be compared between disparate locations and sampling times. Analysis of samples at a minimum monthly frequency using sufficient sample volumes, e.g., 50 L, has shown that C&G are virtually universal in surface water, continuously, and at levels consistent with catchment conditions. Some basic rules of monitoring and data analysis derived from this background information will ensure that monitoring effort and cost are applied in the most efficient and effective manner.