Rotavirus survival in conventionally treated drinking water

Samples of conventionally treated drinking water collected either as effluent (PE) at a treatment plant or out of a tap (TW) in our laboratory were seeded with simian rotavirus SA-11, which closely resembles rotavirus of human origin. The virus, grown in MA-104 cells, was suspended either in distilled water, Earle's balanced salt solution (EBSS), or tryptose phosphate broth (TPB), and added to the water samples to a final concentration of 5.7 X 10(3) plaque-forming units (PFU) per millilitre. After a contact time of 1 h at 22 degrees C, the samples were diluted and plaque assayed. There was no significant reduction in the virus titre in samples of TW (less than 0.05 mg/L free chlorine). The titre also remained almost the same in PE (0.75 mg/L free chlorine) when EBSS or TPB was used for virus suspension. There was, however, nearly a 1 log10 loss in the titre of the virus when it was suspended in distilled water before the contamination of PE. To study the long-term survival of the rotavirus in TW, the inoculated samples (5.0 X 10(4) PFU/mL) were held at either 4 or 20 degrees C in the dark and tested over a period of 64 days. At 20 degrees C it took 64 days to reduce the virus titre by 2 log10, whereas at 4 degrees C the virus titre dropped only 0.7 log10 during the same period. Rotaviruses could, therefore, survive well enough in conventionally treated drinking water to make it a possible vehicle for their transmission.