P Payment

Publications of P Payment

• Removal of indicator bacteria, human enteric viruses, Giardia cysts, and Cryptosporidium oocysts at a large wastewater primary treatment facility.

  Authors: P Payment, R Plante, P Cejka

  Canadian journal of microbiology. 04/2001; 47(3):188-93.

  Pathogens and fecal indicator bacteria occurrence and removal were studied for a period of 6 months at the Montreal Urban Community wastewater treatment facility. With a capacity of about 7.6 millionPathogens and fecal indicator bacteria occurrence and removal were studied for a period of 6 months at the Montreal Urban Community wastewater treatment facility. With a capacity of about 7.6 million cubic metres per day (two billion U.S. gallons per day), it is the largest primary physico-chemical treatment plant in America. The plant discharges a nondisinfected effluent containing about 20 mg/L of suspended matter and 0.5 mg/L of total phosphorus on the basis of average annual concentrations. BDO5 (annual mean) is 75 mg/L before treatment and 32 mg/L after treatment. Samples were collected for a period of 6 months, and they demonstrated that the plant was not efficient at removing indicator bacteria and the pathogens tested. Fecal coliforms were the most numerous of the indicator bacteria and their removal averaged 25%. Fecal streptococci removal was 29%, while Escherichia coli removal was 12%. In untreated sewage, fecal coliforms, E. coli, and human enteric viruses were more numerous in summer and early autumn. Fecal streptococci counts remained relatively similar throughout the period. Clostridium perfringens removal averaged 51%. Giardia cysts levels were not markedly different throughout the study period, and 76% of the cysts were removed by treatment. Cryptosporidium oocyst counts were erratic, probably due to the methods, and removal was 27%. Human enteric viruses were detected in all samples of raw and treated wastewater with no removal observed (0%). Overall, the plant did not perform well for the removal of fecal indicator bacteria, human enteric viruses, or parasite cysts. Supplementary treatment and disinfection were recommended to protect public health. Various alternatives are being evaluated.

• Occurrence of pathogenic microorganisms in the Saint Lawrence River (Canada) and comparison of health risks for populations using it as their source of drinking water.

  Authors: P Payment, A Berte, M Prévost, B Ménard, B Barbeau

  Canadian journal of microbiology. 07/2000; 46(6):565-76.

  A 300-km portion of the Saint Lawrence hydrological basin in the province of Québec (Canada) and 45 water treatment plants were studied. River water used by drinking water treatment plants wasA 300-km portion of the Saint Lawrence hydrological basin in the province of Québec (Canada) and 45 water treatment plants were studied. River water used by drinking water treatment plants was analyzed (6-L sample volumes) to determine the level of occurrence of bacterial indicators (total coliforms, fecal coliforms, and Clostridium perfringens) and pathogens (Giardia lamblia, Cryptosporidium, human enteric viruses). Pathogens and bacterial indicators were found at all sites at a wide range of values. Logistic regression analysis revealed significant correlations between the bacterial indicators and the pathogens. Physicochemical and treatment practices data were collected from most water treatment plants and used to estimate the level of removal of pathogens achieved under cold (0 degree C-4 degrees C) and warm (20 degrees C-25 degrees C) water temperature conditions. The calculated removal values were then used to estimate the annual risk of Giardia infection using mathematical models and to compare the sites. The estimated range of probability of infection ranged from 0.75 to less than 0.0001 for the populations exposed. Given the numerous assumptions made, the model probably overestimated the annual risk, but it provided comparative data of the efficacy of the water treatment plants and thereby contributes to the protection of public health.

• Poor efficacy of residual chlorine disinfectant in drinking water to inactivate waterborne pathogens in distribution systems.

  Authors: P Payment

  Canadian journal of microbiology. 09/1999; 45(8):709-15.

  To evaluate the inactivating power of residual chlorine in a distribution system, test microorganisms (Escherichia coli, Clostridium perfringens, bacteriophage phi-X 170, and poliovirus type 1) wereTo evaluate the inactivating power of residual chlorine in a distribution system, test microorganisms (Escherichia coli, Clostridium perfringens, bacteriophage phi-X 170, and poliovirus type 1) were added to drinking water samples obtained from two water treatment plants and their distribution system. Except for Escherichia coli, microorganisms remained relatively unaffected in water from the distribution systems tested. When sewage was added to the water samples, indigenous thermotolerant coliforms were inactivated only when water was obtained from sites very close to the treatment plant and containing a high residual chlorine concentration. Clostridium perfringens was barely inactivated, suggesting that the most resistant pathogens such as Giardia lamblia, Cryptosporidium parvum, and human enteric viruses would not be inactivated. Our results suggest that the maintenance of a free residual concentration in a distribution system does not provide a significant inactivation of pathogens, could even mask events of contamination of the distribution, and thus would provide only a false sense of safety with little active protection of public health. Recent epidemiological studies that have suggested a significant waterborne level of endemic gastrointestinal illness could then be explained by undetected intrusions in the distribution system, intrusions resulting in the infection of a small number of individuals without eliciting an outbreak situation.

• Sources of variation in isolation rate of Giardia lamblia cysts and their homogeneous distribution in river water entering a water treatment plant.

  Authors: P Payment, A Berte, C Fleury

  Canadian journal of microbiology. 08/1997; 43(7):687-9.

  The objective of this work was to determine if differences in the number of Giardia cysts measured in river water were due to the method itself, the analyst, or real differences in the distributionThe objective of this work was to determine if differences in the number of Giardia cysts measured in river water were due to the method itself, the analyst, or real differences in the distribution of these cysts in water. To minimize the methodological differences, centrifugation only was used as the primary concentration method. Differences were observed between results from different analysts and they were identified as technical errors. Once the method had been well established, cysts were found to be distributed homogeneously in the river water tested. Small differences were observed among samples collected sequentially at the same time, as well as for samples collected on different days or at different times on the same day. The differences reported in the literature in the number of Giardia cysts detected in water samples from the same site could be an artifact of the methods more than true differences in the counts.

• Incidence of Norwalk virus infections during a prospective epidemiological study of drinking water-related gastrointestinal illness.

  Authors: P Payment, E Franco, G S Fout

  Canadian journal of microbiology. 11/1994; 40(10):805-9.

  To determine the seroprevalence of Norwalk virus and whether Norwalk virus contributed to an observed increase in illness in tap water drinkers participating in a prospective epidemiological study,To determine the seroprevalence of Norwalk virus and whether Norwalk virus contributed to an observed increase in illness in tap water drinkers participating in a prospective epidemiological study, sera collected during the study were examined for changes in Norwalk virus antibody titer, using a specific enzyme immunoassay. Antibodies to Norwalk virus were measured in sera collected in March, June and September 1988 and in June 1989, and antibodies were found in 79% of the individuals. Seroprevalence increased with age, being 55% (ages 9-19), 79% (20-39), 87% (40-49), 84% (50-59), and 100% (60 and older). Norwalk infections occurred in 33% of the individuals during the course of the study. The highest rate of infection (expressed as a monthly rate) was observed during the summer of 1988. These results confirm that a large number of infections owing to Norwalk viruses occur throughout the year. A previous seroconversion or a high serum titer were not always protective. Finally, there was no detectable difference in infection rate between consumers of tap water and consumers of water treated by reverse-osmosis units, suggesting that Norwalk virus infections were not responsible for the excess of gastrointestinal illness observed in tap water drinkers during this epidemiological study.

• Blood agar to detect virulence factors in tap water heterotrophic bacteria.

  Authors: P Payment, E Coffin, G Paquette

  Applied and environmental microbiology. 05/1994; 60(4):1179-83.

  Cytolytic colonies were found in 57% of tap water samples, and up to 6% of samples were found to contain bacteria having three or more virulence factors. The factors evaluated were cytotoxicity,Cytolytic colonies were found in 57% of tap water samples, and up to 6% of samples were found to contain bacteria having three or more virulence factors. The factors evaluated were cytotoxicity, hemolysis, cell adherence, and cell invasiveness. Overall, 17% of the samples contained cytolytic colonies that were adherent and hemolytic. Among the media tested, tryptic soy agar with sheep blood (incubated at 35 degrees C for 48 h) was the best medium for the detection of cytolytic colonies. Of the colonies growing on this medium, 13% were cytolytic, whereas on medium R2A, less than 3% were cytolytic. Furthermore, when tryptic soy agar with blood was used, 24% of the samples contained colonies with at least three virulence factors whereas only 5% were positive with R2A. Routine monitoring by using tryptic soy agar with sheep blood is suggested as an appropriate procedure for the detection of bacteria with pathogenic potential in drinking water.

• Clostridium perfringens and somatic coliphages as indicators of the efficiency of drinking water treatment for viruses and protozoan cysts.

  Authors: P Payment, E Franco

  Applied and environmental microbiology. 09/1993; 59(8):2418-24.

  To find the most suitable indicator of viral and parasitic contamination of drinking water, large-volume samples were collected and analyzed for the presence of pathogens (cultivable human entericTo find the most suitable indicator of viral and parasitic contamination of drinking water, large-volume samples were collected and analyzed for the presence of pathogens (cultivable human enteric viruses, Giardia lamblia cysts, and Cryptosporidium oocysts) and potential indicators (somatic and male-specific coliphages, Clostridium perfringens). The samples were obtained from three water treatment plants by using conventional or better treatments (ozonation, biological filtration). All samples of river water contained the microorganisms sought, and only C. perfringens counts were correlated with human enteric viruses, cysts, or oocysts. For settled and filtered water samples, all indicators were statistically correlated with human enteric viruses but not with cysts or oocysts. By using multiple regression, the somatic coliphage counts were the only explanatory variable for the human enteric virus counts in settled water, while in filtered water samples it was C. perfringens counts. Finished water samples of 1,000 liters each were free of all microorganisms, except for a single sample that contained low levels of cysts and oocysts of undetermined viability. Three of nine finished water samples of 20,000 liters each revealed residual levels of somatic coliphages at 0.03, 0.10, and 0.26 per 100 liters. Measured virus removal was more than 4 to 5 log10, and cyst removal was more than 4 log10. Coliphage and C. perfringens counts suggested that the total removal and inactivation was more than 7 log10 viable microorganisms. C. perfringens counts appear to be the most suitable indicator for the inactivation and removal of viruses in drinking water treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

• A randomized trial to evaluate the risk of gastrointestinal disease due to consumption of drinking water meeting current microbiological standards.

  Authors: P Payment, L Richardson, J Siemiatycki, R Dewar, M Edwardes, E Franco

  American journal of public health. 07/1991; 81(6):703-8.

  BACKGROUND: This project directly and empirically measured the level of gastrointestinal (GI) illness related to the consumption of tapwater prepared from sewage-contaminated surface waters andBACKGROUND: This project directly and empirically measured the level of gastrointestinal (GI) illness related to the consumption of tapwater prepared from sewage-contaminated surface waters and meeting current water quality criteria. METHODS: A randomized intervention trial was carried out; 299 eligible households were supplied with domestic water filters (reverse-osmosis) that eliminate microbial and chemical contaminants from their water, and 307 households were left with their usual tapwater without a filter. The GI symptomatology was evaluated by means of a family health diary maintained prospectively by all study families over a 15-month period. RESULTS: The estimated annual incidence of GI illness was 0.76 among tapwater drinkers compared with 0.50 among filtered water drinkers (p less than 0.01). These findings were consistently observed in all population subgroups. CONCLUSION: It is estimated that 35% of the reported GI illnesses among the tapwater drinkers were water-related and preventable. Our results raise questions about the adequacy of current standards of drinking water quality to prevent water-borne endemic gastrointestinal illness.

• Gastrointestinal health effects associated with the consumption of drinking water produced by point-of-use domestic reverse-osmosis filtration units.

  Authors: P Payment, E Franco, L Richardson, J Siemiatycki

  Applied and environmental microbiology. 05/1991; 57(4):945-8.

  During a prospective epidemiological study of gastrointestinal health effects associated with the consumption of drinking water produced by reverse-osmosis domestic units, a correlation wasDuring a prospective epidemiological study of gastrointestinal health effects associated with the consumption of drinking water produced by reverse-osmosis domestic units, a correlation was demonstrated between the bacterial counts on R2A medium incubated at 35 degrees C and the reported gastrointestinal symptoms in families who used these units. A univariate correlation was found with bacterial counts on R2A medium at 20 degrees C but was confounded by the bacterial counts at 35 degrees C. Other variables, such as family size and amount of water consumed, were not independently explanatory of the rate of illness. These observations raise concerns for the possibility of increased disease associated with certain point-of-use treatment devices for domestic use when high levels of bacterial growth occur.

• Fate of human enteric viruses, coliphages, and Clostridium perfringens during drinking-water treatment.

  Authors: P Payment

  Canadian journal of microbiology. 03/1991; 37(2):154-7.

  The elimination of human enteric viruses, coliphages, and Clostridium perfringens was studied during a conventional complete drinking-water treatment process. The respective concentrations (geometricThe elimination of human enteric viruses, coliphages, and Clostridium perfringens was studied during a conventional complete drinking-water treatment process. The respective concentrations (geometric mean) of these microorganisms in 100-L samples of river water were, respectively, as follows: viruses, 79 mpniu (most probable number of infectious units) per 100 L, coliphages, 6565 pfu (plaque-forming units) per 100 L. and clostridia, 11,349 cfu (colony-forming units) per 100 L. After predisinfection, flocculation with alum, and settling, human enteric viruses were not detected in any of the 100-L samples (less than 4 mpniu/100 L), but coliphages were detected in 7 of 14 samples and clostridia in 15 of 16 samples. In filtered water samples, human enteric viruses were detected in 2 of 31 samples, coliphages in 10 of 33, and clostridia in 17 of 33. Finished water was free of human enteric viruses (0/162 samples), but coliphages were detected in one sample (1.5 pfu/100 L) and clostridia in three, at 1.0, 4.1, and 7.0 cfu/100 L. It thus appears that coliphages and clostridia, which are present in larger numbers than viruses in river water and which may have similar resistance to drinking-water treatments, may be useful for estimating the level of treatment attained when large volumes of water (1000 L or greater) are sampled.

• Minimal infective dose of the OSU strain of porcine rotavirus.

  Authors: P Payment, E Morin

  Archives of virology. 02/1990; 112(3-4):277-82.

• Bacterial colonization of domestic reverse-osmosis water filtration units.

  Authors: P Payment

  Canadian journal of microbiology. 12/1989; 35(11):1065-7.

  We have analyzed the bacterial content of water from the reservoirs of 300 reverse-osmosis units installed in households. The heterotrophic plate counts on R2A medium (20 and 35 degrees C) rangedWe have analyzed the bacterial content of water from the reservoirs of 300 reverse-osmosis units installed in households. The heterotrophic plate counts on R2A medium (20 and 35 degrees C) ranged from 0 to 10(7) colony forming units per millilitre (cfu/mL). Most reservoirs contained water with bacterial counts between 10(4) and 10(5) cfu/mL. The bacteria identified were Pseudomonas (not aeruginosa), Alcaligenes or Moraxella, Acinetobacter, Flavobacterium, and Chromobacterium. This report emphasizes the importance of bacterial colonization by heterotrophic bacteria in water reservoirs from domestic reverse-osmosis units.

• Concentration of Giardia lamblia cysts, Legionella pneumophila, Clostridium perfringens, human enteric viruses, and coliphages from large volumes of drinking water, using a single filtration.

  Authors: P Payment, A Bérubé, D Perreault, R Armon, M Trudel

  Canadian journal of microbiology. 11/1989; 35(10):932-5.

  Poliovirus, coliphages, Giardia lamblia cysts, Clostridium perfringens spores, and Legionella pneumophila were concentrated simultaneously in a single pass by sequential filtration of large volumesPoliovirus, coliphages, Giardia lamblia cysts, Clostridium perfringens spores, and Legionella pneumophila were concentrated simultaneously in a single pass by sequential filtration of large volumes of drinking water through 3- and 1-micron wound electronegative fiberglass cartridge filters (25.4 cm). Filtration was performed under acidic conditions (pH 3.5) in the presence of 0.001 M aluminum chloride to enhance adsorption. Elution of all the microorganisms entrapped or adsorbed to the filters was obtained by a slow backwash elution with a 1.5% beef extract solution, pH 9.75, containing 0.5% Tween 80. Tween 80 was shown to enhance recovery of the bacteriophages, bacteria, and parasites. Giardia cysts were efficiently eluted (71%) and could be reconcentrated by low-speed centrifugation and purified by sucrose density gradient flotation at a final recovery of 52%. Legionella pneumophila cells were eluted at 64% and were further concentrated by low-speed centrifugation at an overall recovery of 55%. C. perfringens spores and coliphages were eluted at efficiencies of 82 and 86%, respectively, and reconcentrated with minimal loss by a detergent - protein flotation method. Poliovirus was eluted at 93% and reconcentrated at 78% efficiency by organic flocculation.

• Rapid detection and identification of Legionella pneumophila by a membrane immunoassay.

  Authors: A Bérubé, M Trudel, P Payment

  Applied and environmental microbiology. 07/1989; 55(6):1640-1.

  Legionella pneumophila was detected and identified by an immunoblot assay using a monoclonal antibody specific to serogroups 1 to 8. Samples containing L. pneumophila were plated on buffered charcoalLegionella pneumophila was detected and identified by an immunoblot assay using a monoclonal antibody specific to serogroups 1 to 8. Samples containing L. pneumophila were plated on buffered charcoal yeast extract agar supplemented with glycine, vancomycin, and polymyxin B. After incubation at 35 degrees C for 3 days, colonies were transferred to nitrocellulose membranes by blotting. Simultaneous detection and identification of L. pneumophila were done by treating the membrane with the monoclonal antibody and a peroxidase conjugate to mouse immunoglobulins. A diffuse cross-reaction was observed with Pseudomonas fluorescens colonies, but this was a low-level reaction that could easily be differentiated from the strong specific reactions to L. pneumophila.

• Production and characterization of neutralizing monoclonal antibodies against poliovirus type 1, 2, and 3.

  Authors: P Payment, M Trudel, L Thibodeau, J Lecomte

  Canadian journal of microbiology. 06/1989; 35(5):550-3.

  Neutralizing monoclonal antibodies were produced against a reference vaccine or a reference wild strain of poliovirus type 1, 2, and 3. After 26 fusions, 55 monoclonal antibodies were obtained withNeutralizing monoclonal antibodies were produced against a reference vaccine or a reference wild strain of poliovirus type 1, 2, and 3. After 26 fusions, 55 monoclonal antibodies were obtained with serotype 1 as the immunizing antigen, 180 with serotype 2, and 115 with serotype 3. The neutralizing activity of these monoclonal antibodies was tested first with the two reference strains and then if reactive, against a panel of 10 well-characterized strains of each serotype, 5 vaccinelike (VL) and 5 nonvaccinelike (NVL). All monoclonal antibodies were type specific without reactivity with any of the heterologous strains. There was a wide range of reactivity within the strains of each serotype. Several monoclonal antibodies to serotype 1 reacted with all type 1 strains, while several neutralized strongly all VL strains and weakly one or more of the NVL strains. Most of the 180 monoclonal antibodies to serotype 2 neutralized to various degrees all strains of this serotype and about half reacted very strongly with all homologous strains whether VL or NVL. None could differentiate all VL and NVL homologous strains. Of the 115 monoclonal antibodies to serotype 3, several monoclonal antibodies neutralize to various levels all homologous strains and some can differentiate VL and NVL strains.

• Microbiological and virological analysis of water from two water filtration plants and their distribution systems.

  Authors: P Payment, F Gamache, G Paquette

  Canadian journal of microbiology. 01/1989; 34(12):1304-9.

  The microbial flora of the water produced by two water filtration plants and their drinking water distribution system were evaluated: the Pont-Viau (PV) and the Repentigny (RE) water filtrationThe microbial flora of the water produced by two water filtration plants and their drinking water distribution system were evaluated: the Pont-Viau (PV) and the Repentigny (RE) water filtration plants. Untreated water entering the plants contained 3.6 (PV) and 16.8 most probable number of infectious units (mpniu)/L (RE) enteric viruses and total coliform bacteria counts were 300,000 (PV) and 500,000 cfu/L (RE). Treated water leaving the plant was essentially free of all the bacterial indicators measured (total, stressed, and fecal coliforms; Aeromonas hydrophila; Pseudomonas aeruginosa; Clostridium perfringens; enterococci) as well as of human enteric viruses. Heterotrophic plate counts at 20 and 35 degrees C were low in the freshly treated water leaving the plants, but bacterial regrowth was observed in both distribution systems at all sampling sites. Average counts for the heterotrophic plate count (20 degrees C) were between 10(6) and 10(7) cfu/L and counts were clearly increased with the distance from the plant. The most numerous bacterial genera encountered were Bacillus, Flavobacterium, and Pseudomonas (nonaeruginosa).

• Neutralizing response of rabbits to an experimental rubella subunit vaccine made from immunostimulating complexes.

  Authors: M Trudel, F Nadon, C Séguin, P Payment

  Canadian journal of microbiology. 01/1989; 34(12):1351-4.

  The purpose of this study was to evaluate experimentally the immunogenicity in rabbits of rubella subunits adsorbed to the adjuvant Quil A. The adsorbed viral proteins form structurally definedThe purpose of this study was to evaluate experimentally the immunogenicity in rabbits of rubella subunits adsorbed to the adjuvant Quil A. The adsorbed viral proteins form structurally defined ImmunoStimulating COMplexes (ISCOMs). Rubella ISCOMs were tested for their capacity to induce neutralizing and hemagglutination-inhibiting antibodies, in comparison with a commercial live attenuated vaccine. Rubella ISCOMs were as efficient as the live vaccine in inducing neutralizing and hemagglutination inhibiting antibodies, suggesting the possibility of developing an ISCOMs subunit vaccine.

• Detection of animal and human enteric viruses in water from the Assomption River and its tributaries.

  Authors: P Payment, F Affoyon, M Trudel

  Canadian journal of microbiology. 09/1988; 34(8):967-73.

  Animal enteroviruses, reoviruses, and human enteric viruses were detected in water samples (20 L) from a major river system, the Assomption River in the province of Quebec. Animal enteroviruses,Animal enteroviruses, reoviruses, and human enteric viruses were detected in water samples (20 L) from a major river system, the Assomption River in the province of Quebec. Animal enteroviruses, probably of porcine origin (this region is a major producer of pork), were isolated on porcine cell cultures and were found in 29 to 60% of water samples from the different sites on the river and in 19 to 48% of the water samples from the tributaries. The average concentration of these animal enteroviruses in water from the Assomption River was 2 to 7 mpniu/L (most probable number of infectious units per litre), and that from the tributaries varied from 3 to 24 mpniu/L. Reoviruses were detected in infected cell cultures by an enzyme-linked immunosorbent assay. Their origin is probably avian (broiler chicken farms) or human (untreated domestic waste waters) and they were detected in 19 to 52% of the water samples from the Assomption River at an average concentration of 3 to 12 mpniu/L. In water samples from the tributaries, 5 to 71% of the samples were positive at an average concentration of 5 to 24 mpniu/L. Human enteric viruses were detected in MA-104 cells by an immunoperoxidase assay using human immune serum globulin. They were detected in 13 to 72% of water samples from the Assomption River and 14 to 71% of the water samples from the tributaries. The average concentration of these human enteric viruses in Assomption River water varied from 1 to 12 and from 2 to 145 mpniu/L in water samples from the tributaries.(ABSTRACT TRUNCATED AT 250 WORDS)

• Coliphages and enteric viruses in the particulate phase of river water.

  Authors: P Payment, E Morin, M Trudel

  Canadian journal of microbiology. 08/1988; 34(7):907-10.

  The present study was undertaken to determine if indigenous enteric viruses and coliphages are free or associated with suspended particulate matter in natural waters. River water was filtered onThe present study was undertaken to determine if indigenous enteric viruses and coliphages are free or associated with suspended particulate matter in natural waters. River water was filtered on filters of decreasing porosities (100-0.25 micron) that were pretreated with detergent to eliminate viral adsorption while retaining particulates. This filtered water was refiltered in virus-adsorbing conditions to retain free viruses. The virus-adsorbing filter retained most of the enteric viruses (77.4%) and coliphages (65.8%), which indicated that these viruses were probably free or associated with particles with a diameter of less than 0.25 micron. These observations are important because in water treatment plants small particulates are often the most difficult to eliminate.

• Rapid titration of bovine, caprine and human RS virus by a micro-immunoperoxidase assay using a monoclonal antibody and a permissive ovine kidney cell line.

  Authors: F Bélanger, R Alain, P Payment, J Lecomte, M Trudel

  Journal of virological methods. 07/1988; 20(2):101-7.

  An indirect immunoperoxidase micro-assay, using a continuous cell line derived from ovine kidney cells (OK) and a previously characterized monoclonal antibody (7C2), specific for an exposed andAn indirect immunoperoxidase micro-assay, using a continuous cell line derived from ovine kidney cells (OK) and a previously characterized monoclonal antibody (7C2), specific for an exposed and highly conserved epitope of the fusion protein of different strains of RS virus, was used advantageously to rapidly titrate bovine, caprine and human strains of RSV by either quantal (TCID50) or plaque forming assays. Virus titers, obtained in less than 36 h, were in agreement with those obtained by the conventional plaque assays which required an incubation period of 4 days or more. This assay is also applicable to micro-neutralization of fusion inhibition assays for testing serum or screening monoclonal antibodies.