A. Valentin,
T. Tremblay,
F. Gagnon, et
J.-F. Cartier

Régie régionale de la santé et des services sociaux de la Côte-Nord, Direction de la santé publique

To obtain this report:
quebec.slv2000@ec.gc.ca

The complete report is available in French only

Assessment of various microorganisms as indicators of faecal
contaminationin shellfishes and shellfish growing waters
on the North Shore of the St Lawrence maritime estuary

Valentin, A., T. Tremblay, F. Gagnon, and J.-F. Cartier 2000. Évaluation de la validité des indicateurs de contamination fécale des mollusques bivalves et des eaux coquillières de la rive nord de l'estuaire maritime du Saint-Laurent. Régie régionale de la santé et des services sociaux de la Côte-Nord, Direction de la santé publique, 90 p.

Abstract

The main objective of this study is to generate information on the micro-organisms that could be considered as potential indicators of faecal contamination of molluscs and shellfish growing waters on the North Shore of the St. Lawrence Lower Estuary. The study also aims to evaluate the influence of various environmental parameters (physico-chemical characteristics of water and weather conditions) on the presence and the abundance of the indicators in shellfish growing waters.

Soft-shell clams and water samples were collected between the end of June and the end of September 1999. For the clams, eight rounds of sampling were carried out at nine sites at various locations distributed between Pointe-aux-Outardes and Grandes-Bergeronnes. These sites are exposed to various contamination sources and belong to sectors approved for harvesting, conditionally approved for harvesting or, sectors that are closed to harvesting. Water was collected at ebb tide, twice a week, at one site only (Baie-Laval). Daily weather conditions were obtained from Environment Canada and from the Ministère de l’Environnement du Québec. Presence and abundance of six potential indicators were assessed in clams and water samples. These indicator micro-organisms are Escherichia coli, fecal coliforms, Enterococci sp, somatic coliphages, male coliphages and Clostridium perfringens. The presence of four pathogens was evaluated in the clam samples, namely, Cryptosporidium parvum, Giardia sp, Campylobacter sp and Salmonella sp.

For the clam samples, the capacity of each indicator to represent the pathogen contamination was evaluated by calculating sensitivity, specificity and predictive values. Correspondence analyses were used to describe spatial (between sites) and temporal (between rounds) distributions of potential indicators and pathogens. Influence of physico-chemical and weather parameters on indicator enumeration in shellfish growing waters was evaluated using a principal components analysis (PCA) and a correlation analysis.

Results show that the detection frequency of pathogens in clams is important (90.2%). C. parvum and Giardia sp are the pathogens most often detected, followed to a lesser extent by Campylobacter sp. Salmonella sp are almost always absent. Pathogens are present at all sampling sites; they are found in both the closed sectors and in the sectors open for harvesting. Mollusc consumption represents a significant source of exposure to pathogenic micro-organisms transmitted by the fecal-oral route. This situation is of concern for the consumers health because of the low infectious dose of these pathogens associated to consumers risky behaviours. The importance of cooking molluscs before consumption needs to be emphasized. It is recommended that the traditional steam cooking method be replaced by boiling the molluscs directly in water for at least five minutes.

E coli and fecal coliforms appear to be poor indicators of the pathogen contamination. Their validity seems to be restricted to endemic and point source contamination. Their utility in the evaluation of the microbiological quality of molluscs and shellfish growing waters is discussed.

Comparison of detection frequencies in water and clams suggests a rapid disappearance of E coli and fecal coliforms in the environment. PCA results highlight the role of salinity in this disappearance. They also show that precipitations and turbidity favour the presence of these bacteria. Somatic coliphages emerge as the best indicators of pathogenic contamination. They are also shown to be less vulnerable to environmental conditions than E coli and fecal coliforms. The use of somatic coliphages, turbidity, precipitations and salinity as indicators of the microbiological quality of molluscs and shellfish growing waters is discussed.