Inactivation of Hepatitis A Virus, Other Enteric Viruses and Indicator Organisms in Water by Chlorination

Hepatitis A virus (HAV) and various indicator organisms were mixed together in autoclaved biofilter effluent and broth-enriched tap water, and the survival kinetics of individual organisms after the addition of chlorine were compared. Chlorine was present in the reaction mixtures predominantly in the form of combined residuals. HAV was enumerated by a most probable number dilution assay using PLC/PRF/5 liver cells for propagation of the virus and radioimmunoassay for its detection. In both reaction mixtures HAV survived longer than Escherichia coli, Streptococcus faecalisi, poliovirus type 2, coxsackievirus B5 and reovirus type 3, while it was less resistant than coliphage MS2, coliphage VI (except in tap water), the simian SA-11 rotavirus and Mycobacterium fortuitum. The survival data indicate that viruses (including coliphages) tend to be relatively more resistant to combined chlorine residuals than bacteria, while bacteria tend to be relatively more resistant to free chlorine residuals than viruses. Coliform bacteria may thus be fairly reliable indicators of the virological safety of waters disinfected by free chlorine residuals, but not of waters disinfected by combined chlorine residuals, as in the case of the chlorination of wastewater or the chloramination of drinking-water supplies. The relatively high resistance to combined chlorine residuals of HAV and SA-11 virus (which is closely related to human rotavirus) emphasizes the shortcomings of methods available for virological water analysis because they do not detect HAV and rotavirus. The results support views that the virological safety of all chlorinated waters can be reliably monitored by means of practical indicator systems consisting of appropriate combinations of determinands such as the standard plate count, coliform bacteria, coliphages, acid-fast bacteria and faecal streptococci.