Effect of rainfall on Giardia and crypto

Rainfall increases concentrations of Giardia and Cryptosporidium through its influence on turbidity, flow volume, and possibly other unidentified factors. An investigation of the variability of concentrations of Giardia cysts and Cryptosporidium oocysts in the Delaware River was conducted in 1996 at Trenton, N.J. A goal of the study was to examine the relationship between concentrations of Giardia and Cryptosporidium and a variety of more easily measured microbial, water quality, and meteorological parameters. A positive correlation (Spearman rank; p < 0.05) was demonstrated between concentrations of Giardia cysts or Cryptosporidium oocysts and 15 other parameters. Increased concentrations of Giardia and Cryptosporidium as well as a variety of other microorganisms were associated with rainfall. The effect of rainfall on parasite concentrations is due in part to increased particulate matter in the water column following surface runoff and resuspension of river bottom and storm drain sediment.