Report No FR0213

VIRUSES IN SURFACE WATERS -
OCCURRENCE AND ENVIRONMENTAL CONTROL

FR0213

June 1991

SUMMARY

I OBJECTIVES

To report on the incidence and stability of enteric viruses in coastal waters, their effects on compliance with the EC bathing water Directive standards, and their implications for human health.

II REASONS

Under the Directive 76/160/EEC, enteroviruses must be absent from 95% of 10-litre samples, but monitoring is not required unless inspection shows that they are present or conditions have deteriorated. Development of monitoring capabilities and widespread virological sampling in the bathing season 1989 have shown that enteroviruses were detected at 73 out of 440 beaches in waters of satisfactory bacteriological quality. If the ubiquity and longevity of enteroviruses in the sea is confirmed it will have financial implications for proposed marine treatment schemes for bringing unsatisfactory beaches into compliance by 1995.

III CONCLUSIONS

  1. Currently there is insufficient data to assess the value of enteroviruses as health-related indicators.
  2. Enteroviruses should be regarded as an indicator of faecal contamination, albeit one which is more closely related to the probable causative agents of infections in users of recreational waters than faecal coliform organisms.
  3. Thorough and valid assessment of the occurrence and significance of viruses in marine waters is hampered by a lack of reliable information, caused in part by inefficient analytical techniques.
  4. Assessment of the results of monitoring of UK identified EC beaches reveals that compliance with the faecal coliform standard does not ensure compliance with the enterovirus standard. Furthermore differences in the pattern of compliance between years suggests that the monitoring obligations for one year cannot be anticipated on the basis of results from previous years.
  5. The information currently available from UK epidemiological studies does not yet permit direct estimation of risk to health of bathers in the sea from prevailing levels of enteroviruses.
  6. Published data on viral decay rates are too variable to allow a T90 value to be identified with confidence for use in predictive modelling studies. Similarly there is a general lack of data on the viral loading of discharges.

V RECOMMENDATIONS

It is recommended that the following topics be considered for further research.

  1. Relationships between health effects in recreational water users and concentrations of viruses can only be established by epidemiological study. Although prospective and cohort studies are planned for 1991/92 and 1992/93 it is recommended that provision of additional funding to allow more intensive monitoring of viruses should be considered.
  2. There are priority research needs in several areas of the development of viral analysis techniques which need to be addressed before more valid data on the occurrence of viruses can be obtained.
  3. The current lack of information on the viral loadings of sewages, effluents and other sources needs to be addressed by a thorough, well-planned monitoring programme.
  4. Although there have always been methodological problems associated with studying the decay of enteric organisms, it is recommended that WRc's experience in this topic be utilised to determine T90 values for enteroviruses and rotaviruses.
  5. Further modelling studies should be carried out once better information on decay rates and loads has been obtained.

V RESUME OF CONTENTS

Current information on the incidence and sources of enteroviruses is reviewed. The numbers of viruses in sewage effluents were seen to depend on the virological quality of the raw sewage and on the type of treatment given. In general most types of treatment did not significantly decrease the virus content of wastewaters. Virus levels in rivers and coastal waters were found to be very variable and as a consequence unpredictable. The review highlights shortcomings in current analytical techniques, and a lack of standardisation of procedures could be seen to cause some of the apparent variation in virus levels.

Statistical analysis of the 1989 and 1990 bathing beach monitoring results demonstrated very clearly that there is no correlation between compliance with the faecal coliform and enterovirus standards. In practical terms this means that even if a beach complies with the faecal coliform standard the presence of viruses should still be suspected.

The available information on possible associations between microbiological quality of marine and fresh waters used for recreation and health effects reported by water sports participants was studied. It did not reveal a relationship in which viral conc entrations can be directly related to health effects. A surprising result from this detailed examination of data was a high degree of correlation between counts of faecal coliform bacteria and enterovirus concentrations when all available data were pooled. Such correlation was not seen in individual studies though.

Published data on viral decay rates was found to be too variable to allow a T90 value to be identified with confidence for use in predictive modelling studies. Future virological research needs are identified.

The full report can be obtained on application to the Foundation

Copies of the report are available from FWR, price 25.00, less 20% to FWR Members.