A trial of biosecurity as a means to control Campylobacter infection of broiler chickens

Decontamination of poultry carcasses using steam or hot water in combination with rapid cooling, chilling or freezing of carcass surfaces

The effects of the application of steam at atmospheric pressure for times up to 20 s on the numbers of inoculated Campylobacter jejuni and Escherichia coli on whole chicken carcasses were investigated in a pilot steam cabinet. Steam treatments reduced the numbers of C. jejuni AR6 by ca. 1.8, 2.6 and 3.3 log(10) cfu cm(-2) in 10, 12 and 20 s, respectively. Corresponding reductions in numbers of E. coli K12 were 1.7, 2.3 and 2.8 log(10) cfu cm(-2). However, such treatments caused the skin to shrink and change colour. The optimum treatment for maximum reductions of C. jejuni and E. coli, least skin shrinkage and change of colour was concluded to be <12 s. Further work was carried out to determine whether a modified air chilling system in combination with steam or hot water decontamination treatments could be used to reduce numbers of pathogens, particularly campylobacters, on the surface of poultry carcasses. Whole chicken carcasses inoculated with C. jejuni and E. coli were either not treated, treated with steam at atmospheric pressure for up to 10 s or treated with hot water at 80 degrees C for up to 20 s, then either chilled by crust freezing, chilled at 0 degrees C, or chilled at 15 degrees C, in a pilot chilling chamber. The optimum combination was treatment with water at 80 degrees C for 20 s followed by crust freezing, which reduced the numbers of C. jejuni and E. coli by ca. 2.9 and 3.2 log(10) cfu cm(-2), respectively, without extensive degradation of carcass appearance.

Adoption of biosecurity practices in the Australian poultry industries

OBJECTIVE

To determine the level of adoption within the Australian poultry industries of a range of standard biosecurity practices.

DESIGN

A questionnaire survey of owners and managers of 1753 commercial poultry farms. Procedure Information was collected by telephone or in person from the owners and managers of poultry farms. Data were entered onto an Excel spreadsheet and analysed using the statistical tools within Excel.

RESULTS

The response rates to the questionnaire for the chicken meat, egg, duck and turkey sectors were 94%, 37%, 92% and 96% respectively. Within the chicken meat sector, the adoption rate exceeded 98% for 11 practices with only the rates for appropriate disposal of spent litter/manure (94%) and development of farm level biosecurity plans (88%) falling below this level. Adoption rates for all practices had increased or remained at 100% since the last survey conducted in 2001. Integrated companies in the turkey and duck sector also reported high levels of adoption for most biosecurity practices although rates for the use of fresh litter, cleaning of sheds between batches of birds and maintenance of single age flocks were lower than in the chicken meat sector. Adoption rates for biosecurity practices on independently owned farms in the turkey and duck sectors were lower than for farms operated by integrated companies.

CONCLUSIONS

Farms in the chicken meat, turkey and duck sectors of the Australian poultry industries have a high level of adoption of biosecurity practices with only a small proportion of farms needing to further enhance their biosecurity.

A cross-sectional survey of Australian chicken farms to identify risk factors associated with seropositivity to Newcastle-disease virus

Several outbreaks of virulent Newcastle-disease occurred in Australia in 1998-2000. We conducted a cross-sectional survey of 753 Australian chicken farms to identify risk factors associated with the seroprevalence of chicken flocks with Newcastle-disease virus (NDV). We had a 99.7% response rate to the survey and the overall prevalence of NDV seropositive farms was 39.8%. Associations were analysed for the layer, chicken-meat and breeder production sectors in sector-specific logistic-regression models using 187, 198 and 146 farms, respectively. In the layer sector, increased risk of seroprevalence was associated with increasing age of the chickens, and decreased risk when the nearest-neighbour poultry farm was >10 km distant (odds ratio (OR)=0.30). In the chicken-meat sector, increased risk of seroprevalence was associated with location in the Sydney basin (OR=13.67), eastern Victoria (OR=26.10) or western Victoria (OR=5.43), and decreased risk when the nearest-neighbour poultry farm was greater than 0.5 km distant (OR=0.34). In the breeder sector, increased risk of seroprevalence was associated with increasing age of the chickens, the presence of wild birds on the farm (OR=5.28) and location in eastern Victoria (OR=16.19). A conditional logistic-regression for 112 pairs of farms matched for age, survey region and production sector identified a distance of >1.0 km to the nearest-neighbour poultry farm (OR=0.24) and ownership by owner 2 (OR=0.02), owner 5 (OR=0.11) or owner 9 (OR=0.25) as significant in reducing the risk of NDV seroprevalence. Our survey found that high levels of biosecurity and hygiene practices had been adopted by most farms.

The Occurrence of Campylobacter Species in Hungarian Broiler Chickens from Farm to Slaughter

The reported number of human enteric diseases caused by thermotolerant campylobacters increased in the last few decades worldwide. The microorganism gets into the food chain mostly with poultry meat or meat products. We are not aware of the way the campylobacters infect the broiler flocks, and there is little information about the real prevalence, about the reaction of thermotolerant campylobacters to the environmental factors and about the possibilities of elimination of the bacteria from the food chain. As a part of the long study, samples were collected from a broiler flock from the first day of life to the slaughter of the animals, in summer and in winter. In the summer period, at the first two sampling days (days 0 and 12) all of the samples were negative. At day 26, one cloaca sample, one sample from the surface of the wall near the ventilation aperture and an insect-sample were positive. At day 42, we found Campylobacter spp. on every sampling point at the slaughterhouse. In the winter period, we could not find Campylobacter spp. either from 0 day old, or from 10- and 31-day-old chickens, but we found them at 42 days of age on the slaughter plant. At the slaughtering place, 93.3% of the live birds were infected with Campylobacter spp., and at the end of the processing line, the infection rate was 100%. We could isolate campylobacters from the hands of the workers and from the processing environment as well. Out of the positive samples, 95.5% was contaminated with Campylobacter jejuni.

Evaluation of the efficacy of a peroxygen disinfectant-filled footmat for reduction of bacterial load on footwear in a large animal hospital setting

OBJECTIVE-To compare the efficacy of a peroxygenbased disinfectant used in footbaths with the efficacy of the same disinfectant used in footmats for reducing bacterial contamination of footwear in a large animal hospital. DESIGN-Prospective study. SAMPLE POPULATION-Bacteria recovered from the soles of rubber boots after experimental microbial contamination and exposure to disinfectant solutions or water (water-treated control boots) or no treatment (untreated control boots). PROCEDURES-Investigators contaminated boots by walking through soiled animal bedding. Swab samples were collected from the sole of 1 untreated boot (right or left); the other boot was treated as investigators stepped through a disinfectant-filled footbath, a disinfectant-filled footmat, or water-filled footmat. Samples were collected 10 minutes after each treatment. Differences in numbers of bacteria recovered from treated and untreated boots were analyzed. RESULTS-Mean bacterial counts from peroxygentreated boots were 1.3 to 1.4 log(10) lower (95.4% to 99.8%) than the counts from untreated boots. Results were similar for footmat- and footbath-treated boots. In contrast, there were no statistically detectable differences in mean bacterial counts in samples collected from water-treated or untreated boots. CONCLUSIONS AND CLINICAL RELEVANCE-Results suggest that footmats and footbaths containing peroxygenbased disinfectant are effective in reducing bacterial contamination on the soles of boots when used in conditions representative of large animal hospitals. Similar results were achieved with use of either footmats or footbaths. The use of footbaths and footmats containing effective disinfectants may help decrease the risk for spread of nosocomial infection but should not be expected to sterilize footwear.

Risk factors for Campylobacter spp. colonization in broiler flocks in Iceland

We sampled 1,091 Icelandic broiler flocks at slaughter from May 2001 to December 2003 to determine the prevalence of, and investigate risk factors for the presence of, Campylobacter spp. at the flock level. Approximately 15% of the flocks were positive for Campylobacter spp.; most (95%) of the infected flocks being raised during the months of April-September. Based on the data from the latter months, and using multivariable logistic regression with random effects for herd, we found that the odds of a flock being positive for Campylobacter spp. increased with age and flock size. Additionally, vertical ventilation systems were strongly associated with positive flocks (OR=5.3). After controlling for these variables, we found no evidence of an effect of: year; company; Campylobacter being carried over from one flock to the next; time interval between flocks; using (at the hatcheries) eggs laid on the floor; density of bird housing, or the number of catch lots a flock was divided into for slaughtering purposes on the risk of a Campylobacter-positive flock.

Evaluation of the effects of footwear hygiene protocols on nonspecific bacterial contamination of floor surfaces in an equine hospital

OBJECTIVE

To evaluate the effects of footwear hygiene protocols on bacterial contamination of floor surfaces in an equine hospital.

DESIGN

Field trial.

PROCEDURES

Footwear hygiene protocols evaluated included use of rubber overboots with footbaths and footmats containing a quaternary ammonium disinfectant, rubber overboots with footbaths and footmats containing a peroxygen disinfectant, and no restrictions on footwear type but mandatory use of footbaths and footmats containing a peroxygen disinfectant. Nonspecific aerobic bacterial counts were determined via 2 procedures for sample collection and bacterial enumeration (contact plates vs swabbing combined with use of spread plates), and the effects of each footwear hygiene protocol were compared.

RESULTS

There were no consistent findings suggesting that any of the protocols were associated with differences in numbers of bacteria recovered from floor surfaces. Although there were detectable differences in numbers of bacteria recovered in association with different footwear hygiene protocols, differences in least square mean bacterial counts did not appear to be clinically relevant (ie, were < 1 log10).

CONCLUSIONS AND CLINICAL RELEVANCE

Although cleaning and disinfection of footwear are important aids in reducing the risk of nosocomial transmission of infectious agents in veterinary hospitals, the numbers of aerobic bacteria recovered from floor surfaces were not affected by use of rubber overboots or the types of disinfectant used in this study. Further study is warranted to evaluate the usefulness of footwear hygiene practices relative to their efficacy for reducing transmission of specific pathogens or decreasing nosocomial disease risk.

Dynamics of Campylobacter spp. spread investigated in 14 broiler flocks in Switzerland

Ten conventional and four extensive outdoor broiler flocks, distributed over nine farms, were investigated twice per week during a 35-58-day rearing period to observe the dynamics of Campylobacter spp. spread within these flocks. Strains isolated during this period were genotyped by restriction fragment length polymorphism analysis of the flaA gene and macrorestriction profiling with pulsed field gel electrophoresis. A total of 4112 samples were collected; 157 (3.8%) of these samples were Campylobacter positive, with all C. jejuni. The positive samples were distributed over three conventional and two extensive outdoor flocks on five farms. These five positive flocks were colonized from the fifth to the seventh week of age and remained colonized until slaughter. Each of the flocks showed a flock-specific genotype of Campylobacter that predominated until slaughter. Presuming different ways of entry, a combination of this fact and the observed dynamics of C. jejuni spread within the flocks indicates that a single source from the environment may have been responsible for the colonization of each flock. These conclusions may serve to further develop combat strategies at farm level.

Sources of Campylobacter spp. colonizing housed broiler flocks during rearing

The study aimed to identify sources of campylobacter in 10 housed broiler flocks from three United Kingdom poultry companies. Samples from (i) the breeder flocks, which supplied the broilers, (ii) cleaned and disinfected houses prior to chick placement, (iii) the chickens, and (iv) the environments inside and outside the broiler houses during rearing were examined. Samples were collected at frequent intervals and examined for Campylobacter spp. Characterization of the isolates using multilocus sequence typing (MLST), serotyping, phage typing, and flaA restriction fragment length polymorphism typing was performed. Seven flocks became colonized during the growing period. Campylobacter spp. were detected in the environment surrounding the broiler house, prior to as well as during flock colonization, for six of these flocks. On two occasions, isolates detected in a puddle just prior to the birds being placed were indistinguishable from those colonizing the birds. Once flocks were colonized, indistinguishable strains of campylobacter were found in the feed and water and in the air of the broiler house. Campylobacter spp. were also detected in the air up to 30 m downstream of the broiler house, which raises the issue of the role of airborne transmission in the spread of campylobacter. At any time during rearing, broiler flocks were colonized by only one or two types determined by MLST but these changed, with some strains superseding others. In conclusion, the study provided strong evidence for the environment as a source of campylobacters colonizing housed broiler flocks. It also demonstrated colonization by successive campylobacter types determined by MLST during the life of a flock.

No association between partial depopulation and Campylobacter spp. colonization of Dutch broiler flocks

AIMS

To determine whether an association exists between partial depopulation of a flock and increased Campylobacter colonization in that flock.

METHODS AND RESULTS

Data from 1737 flocks of two Dutch integrators were used. Flocks that experienced partial depopulation were defined as 'exposed' and those that did not as 'nonexposed'. Multivariable modelling was accomplished with, in addition to 'exposure', the independent variables 'age of broilers at slaughter' and 'season' to adjust for possible confounding. The response variable was 'Campylobacter colonization'. The odds ratio (OR) for partial depopulation for integrator A was 0.8 [95% CI (0.4, 1.8)]; for integrator B the OR = 0.8 [95% CI (0.5, 1.3)]. Age and season were confounders: the difference in Campylobacter status between exposed and nonexposed flocks of integrator A could be explained by both variables; for integrator B, only season was associated with Campylobacter status.

CONCLUSIONS

We found no significant association between partial depopulation and an increased risk of Campylobacter colonization among broiler flocks at final depopulation.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study demonstrates that Campylobacter colonization in a broiler flock is not influenced by the partial depopulation of that flock.

Survival of Campylobacter jejuni in waterborne protozoa

The failure to reduce the Campylobacter contamination of intensively reared poultry may be partially due to Campylobacter resisting disinfection in water after their internalization by waterborne protozoa. Campylobacter jejuni and a variety of waterborne protozoa, including ciliates, flagellates, and alveolates, were detected in the drinking water of intensively reared poultry by a combination of culture and molecular techniques. An in vitro assay showed that C. jejuni remained viable when internalized by Tetrahymena pyriformis and Acanthamoeba castellanii for significantly longer (up to 36 h) than when they were in purely a planktonic state. The internalized Campylobacter were also significantly more resistant to disinfection than planktonic organisms. Collectively, our results strongly suggest that protozoa in broiler drinking water systems can delay the decline of Campylobacter viability and increase Campylobacter disinfection resistance, thus increasing the potential of Campylobacter to colonize broilers.

Phage therapy reduces Campylobacter jejuni colonization in broilers

The effect of phage therapy in the control of Campylobacter jejuni colonization in young broilers, either as a preventive or a therapeutic measure, was tested. A prevention group was infected with C. jejuni at day 4 of a 10-day phage treatment. A therapeutic group was phage treated for 6 days, starting 5 days after C. jejuni colonization of the broilers had been established. Treatment was monitored by enumerating Campylobacter colony forming units (CFU) and phage plaque forming units (PFU) from caecal content. Counts were compared with control birds not receiving phage therapy. A clear 3 log decline in C. jejuni counts was initially observed in the therapeutic group, however, after 5 days bacterial counts stabilized at a level 1 log lower than that of the control group. Colonization of C. jejuni in the prevention group was delayed by the treatment and after an initial 2 log reduction, colonization stabilized within a week at levels comparable to the therapeutic group. The CFU and PFU counts displayed opposing highs and lows over time, indicative of alternating shifts in amplification of bacteria and phages. There were no adverse health effects from the phage treatment. Two different phages were combined as therapeutic treatment of Campylobacter positive chickens challenged at the age approaching broiler harvest. This again resulted in a significant decrease in Campylobacter colonization. We conclude that phage treatment is a promising alternative for reducing C. jejuni colonization in broilers.

Evaluation of the efficacy of disinfectant footbaths as used in veterinary hospitals

OBJECTIVE

To evaluate efficacy of 2 disinfectants as used in footbaths in veterinary hospitals for reducing bacterial contamination of footwear.

DESIGN

Prospective study.

SAMPLE POPULATION

Bacteria collected from the soles of rubber boots after experimental contamination and exposure to disinfectant solutions or control conditions.

PROCEDURES

Investigators contaminated boots by walking through soiled straw animal bedding. Swab samples were collected from the sole of 1 boot (right or left) without treatment. The other boot was briefly immersed in a disinfectant solution (either a quaternary ammonium compound [QAC] or a peroxygen compound) or water, and samples were collected after 7 minutes. Differences associated with the experimental treatments were analyzed statistically. Veterinary teaching hospitals (VTHs) in the United States and Canada were contacted to obtain information about the use of footbaths.

RESULTS

Mean bacterial concentrations from peroxygen-treated boots were 67% to 78% lower, compared with samples taken from untreated boots. In contrast, there were no statistically detectable differences in mean bacterial concentrations in samples taken from QAC- or water-treated boots, compared with control boots. Disinfectant footbaths were reportedly used in 30 of 31 VTHs.

CONCLUSIONS AND CLINICAL RELEVANCE

Disinfectant solution containing peroxygen applied in a footbath reduced bacterial concentrations on rubber boots under conditions representative of those found in VTHs. Footbaths are commonly used as a method to control infectious diseases in veterinary hospitals. Disinfectant footbaths should not be expected to sterilize footwear, but they may help in reducing the risk for nosocomial infection when used with effective disinfectants.

Survival analysis on aggregate data to assess time to sero-conversion after experimental infection with Bovine Leukemia virus

Bovine Leukemia virus (BLV) is a ubiquitous retrovirus that affects mainly cattle. Knowledge of the precise moment of infection is fundamental for identification and evaluation of factors related to BLV transmission. Systematic reviews and meta-analyses provide good evidence on the effects of medical interventions. The objectives were to estimate time to sero-conversion after experimental infection using data from retrieved literature and to detect factors that may influence the length of that interval using survival analysis on pooled data. An analysis using aggregate data from 36 studies totalling 438 observations was performed. From this, four sets were created and analysed by interval-censored accelerated failure time models (AFT) with different distributions (exponential, Weibull, log-logistic, lognormal and generalized gamma), and some variants of the Cox model (Andersen-Gill, smoothing splines) with and without a frailty effect. The AFT gamma model fit best and the estimated median time to sero-conversion in the null model was 57 days (95% confidence interval (CI): 49; 75) using all data and 47 days (95% CI: 39; 55) when only studies using experimental inoculation were considered. Some factors were consistently associated with time to sero-conversion. These included exposure by animal-to-animal contact (resulting in a seven-fold increase in time to sero-conversion compared to direct inoculation), diagnostic method to detect sero-conversion (time to sero-conversion was 1.4 times shorter when AGID was used compared to ELISA), and transmission by insect bites (biological media) delayed sero-conversion 2.3 times compared transmission via needles or other inanimate media. After fitting a frailty Cox model, results showed that sero-conversion in susceptible animals after infection using donors, in which presence of virus before the experiment started was confirmed, increased the hazard of sero-conversion two times in comparison with donors in which virus presence was not confirmed before start of the experiment. Inoculation with blood decreased the hazard 2.5 times in comparison with lymphocyte suspensions. Heterogeneity due to different research groups was also present. Finally, a Cox model with smoothing splines contained three variables: research group, route of inoculation and a non-linear spline for infective dose. In conclusion, it can be stated some factors that influence the time to sero-conversion were identified and quantified and that a moderate influence of research centre existed. These results may contribute to the estimation of the most probable times of infection in field conditions and in a better evaluation of control measures.

Pulsed-field gel electrophoresis types of Campylobacter spp. in Danish turkeys before and after slaughter

In this study, seven Danish turkey flocks were investigated at the farm, on arrival to the slaughterhouse, and during and after slaughter. Flocks were selected based on their Campylobacter spp. status at the farm and three Campylobacter negative and four Campylobacter positive flocks were included in the study. At the slaughterhouse, 70-75 samples were collected at different points from the shackling station to packaging of the final meat cuttings. Samples included cloacal swabs, neckskin, liver, heart, meat and environmental samples. Detection of Campylobacter was carried out by conventional culture and by the EiaFoss system (Foss Electric, Hilleroed, Denmark) for detecting Campylobacter spp. in food, using Preston Broth as enrichment medium. The two methods were compared and sensitivities and specificities were calculated using the conventional culture as gold standard. The three negative flocks were consistently negative from the farm and all through processing. Among the samples from the positive flocks, the frequency of positive samples obtained at the slaughterhouse varied. The frequency of positive samples obtained from the four positive flocks varied and was found to be 4%, 49%, 87% and 96%, respectively. In 31 out of 424 samples, discrepancies were observed between results obtained by the EiaFoss system and the conventional culture technique. The sensitivity for the EiaFoss system was calculated to be 0.94 for meat and neckskin samples. A total of 161 strains were genotyped by pulsed-field gel electrophoresis (PFGE) in order to investigate possible changes in carriage of Campylobacter spp. strains during processing. In three flocks, only one PFGE type was encountered in samples collected at the farm level and, in one flock, two different types were observed. In two flocks, the strain from the farm was also isolated in samples collected at the slaughterhouse. Changes in carriage were observed in two flocks during processing, in particular post chilling.

Genotype dynamics of Campylobacter jejuni in a broiler flock

We investigated the genotype diversity and dynamics of Campylobacter in a commercial broiler flock during rearing and slaughter. In total, 220 Campylobacter jejuni isolates collected on four sampling occasions during rearing and from routine sampling during slaughter were subtyped by SmaI macrorestriction and pulsed-field gel electrophoresis, PFGE. Eight different SmaI types were found. During rearing, a subsequent addition of genotypes occurred, with two SmaI types found at 2 weeks of age and six types on the day before slaughter. All types that were detected in more than one isolate were also found on all succeeding sampling occasions, including the slaughter sampling. Two new types were found in the slaughter samples. In two-thirds of the individual birds sampled the day before slaughter, more than one SmaI type were found, although there was a clear tendency for dominance of one type in individual birds. Our results show that multiple genotypes of C. jejuni may be present in a commercial broiler flock during rearing and even in gastrointestinal tracts of individual birds. Both recurring environmental exposure and genetic changes within the population may explain the genotype diversity. Although the distribution of genotypes varied between different sampling occasions, we found no indication that any subtype excluded another during the rearing of the broiler flock.

Prevalence and clonal diversity of Campylobacter jejuni from dairy farms and urban sources

AIM

To investigate the role of free-living animals such as sparrows, rodents and flies as potential reservoirs of Campylobacter spp on a dairy farm, and to assess the genetic diversity among Campylobacter isolates from the farm and an urban source.

METHODS

A total of 290 samples (bovine, passerine and rodent faeces, and whole flies) were collected from a large commercial dairy farm in the Manawatu district in New Zealand, and from faeces from urban sparrows in a nearby city. Other samples collected from the dairy farm included five from silage, two from aprons worn by workers during milking, two from workers' boots and two from water in troughs in a paddock. Isolates of thermophilic Campylobacter spp were identified morphologically and phenotypically and further characterised molecularly using pulsed-field gel electrophoresis (PFGE) and the restriction enzyme SmaI.

RESULTS

Campylobacter jejuni was the only Campylobacter species isolated from all samples. The highest prevalence was found in faeces from dairy cows (54%), followed by faeces from sparrows from the urban area (40%) and the farm (38%), and from rodents (11%) and whole flies (9%). Other samples from the farm environment such as silage, trough water, and workers' aprons and boots were also positive for C. jejuni. Of the 22 restriction patterns obtained, seven were common to more than one source.

CONCLUSIONS

Cattle, sparrows, rodents and flies are potential reservoirs of C. jejuni on dairy farms. Identical clones of C. jejuni carried by cattle, sparrows, flies and rodents probably indicate a common source of infection. The high level of asymptomatic carriage of C. jejuni by healthy dairy cows could be sufficient to maintain infections within the dairy farm surroundings via environmental contamination.

Campylobacter colonization of sibling turkey flocks reared under different management conditions

Uncertainty exists concerning the key factors contributing to Campylobacter colonization of poultry, especially the possible role of vertical transmission from breeder hens to young birds. A longitudinal study of Campylobacter colonization was performed in two sibling pairs of turkey flocks (four flocks total). Each pair of sibling flocks shared breeder hen populations and was obtained from the same hatchery. One flock of each pair was grown on a commercial farm, and the other was grown in an instructional demonstration unit (Teaching Animal Unit [TAU]). Flocks were located within a 60-mi (96.8-km) radius. The time of placement, feed formulations, stocking density, and general husbandry were the same for both flocks, and each flock was processed at a commercial processing plant following standard feed withdrawal and transport protocols. Both flocks grown on the commercial farms became colonized with Campylobacter between weeks 2 and 3 and remained colonized until processing. Between 80 and 90% of isolates were Campylobacter coli, and the remainder were Campylobacter jejuni. In contrast, neither C. coli nor C. jejuni were isolated from either of the TAU flocks at any time during the production cycle. None of the fla types of Campylobacter from the breeders that provided poults to one of the commercial flocks matched those from the progeny. These results failed to provide evidence for vertical transmission and indicate that this type of transmission either did not occur or was not sufficient to render the TAU turkey flocks Campylobacter positive. Management practices such as proper litter maintenance, controlled traffic between the TAU farm and other turkey flocks, and other less well-defined aspects of turkey production were likely responsible for the absence of Campylobacter in the TAU flocks before harvest.

Effect of Organic Acids in Drinking Water for Young Broilers on Campylobacter Infection, Volatile Fatty Acid Production, Gut Microflora and Histological Cell Changes

Water is a prominent vehicle for Campylobacter spread throughout a chicken flock. The aim of this study was to evaluate the effect of organic acids administered through the drinking water, as a decontamination method, on gut microflora and the development of lesions in the gastrointestinal tracts of young broilers inoculated with 2 different doses of Campylobacter. The results revealed that most of the chickens were infected with Campylobacter at the end of the experiment. The drinking water was free of Campylobacter throughout the study. No difference of volatile fatty acid levels between treatment and control groups was observed in the crop and cecal contents. In the cecal contents, the total aerobic bacteria numbers were significantly higher in the treatment groups compared with the control groups (P < 0.01 and P < 0.04, respectively). Moreover, no damaged epithelial cells were observed in the chicken gut due to consumption of acidified drinking water. Acidified drinking water could therefore play a crucial role in a biosecurity strategy of preventing Campylobacter spread via drinking water in broiler flocks.

Risk factors for the presence of Campylobacter spp. in Dutch broiler flocks

The campylobacter status of 495 broiler flocks sampled in The Netherlands between April 1997 and December 2000 was related to farm- and flock-specific information obtained from questionnaires to identify potential risk factors for campylobacter presence. Approximately 30% of the flocks tested positive for Campylobacter spp. in at least one pooled faecal sample. Multivariable logistic regression showed significant risk increments for: ages 29-35 days (OR = 2.34) and 36-42 days (OR = 3.96) compared to 22-28 days; > or =5 broiler houses on the premises (OR = 3.02); the presence of other farm animals on the farm (OR = 1.88); the presence of animals on farms within 1 km (OR = 9.56); and summer (OR = 3.48) and fall (OR = 2.59) compared to winter. Furthermore, hatcheries differed (ORs from 5.42 to 20.2), although this variable showed strong collinearity with the variables explaining feed mill and integrated poultry operations. We also identified interaction in which an increased risk from children entering the broiler house (OR = 28.0) was diminished by the use of broiler-specific workclothes. Population attributable fractions (PAFs) suggested that animals on farms within 1 km (PAF = 0.76) and hatchery (PAF = 0.67) had the highest impacts on campylobacter presence in Dutch broiler flocks. These factors, however, lack an easy interpretation of the mechanism behind the suggested effect.

A demonstration of interval-censored survival analysis

Interval-censoring occurs in survival analysis when the time until an event of interest is not known precisely (and instead, only is known to fall into a particular interval). Such censoring commonly is produced when periodic assessments (usually clinical or laboratory examinations) are used to assess if the event has occurred. My objectives were to raise awareness about interval-censoring including its existence, the potential ramifications of ignoring its existence, the different types of interval-censored data, and the analytical methods to analyze such data (including availability in standard statistical software). Asynchronous interval-censored survival analysis was demonstrated by parametric evaluation of risk factors for the time to first detected shedding of Salmonella muenster (identified by repeated periodic fecal cultures) for a herd of dairy cows. These results were compared with those from survival analyses which ignored or approximated the interval-censoring. Ignoring or approximating the asynchronous interval-censoring in the survival analysis generally resulted in the risk factors' regression coefficients having the same signs and a decrease (often >50%) in their absolute size. All the standard errors from the three methods of approximating the interval-censoring were <40% of their interval-censored counterparts. The conclusions drawn from the asynchronous interval-censored analysis versus those from the approximations varied dramatically. (The general conclusion from the approximations was that none of the risk factors for this example warranted further consideration.) That ignoring or approximating the left- and interval-censored nature of the dependent variable resulted in biased results was consistent with the literature. In the currently available asynchronous interval-censored models, the inclusion of time-dependent covariates that vary continuously is awkward. Statistical models for the semi-parametric estimation of asynchronous interval-censored survival analysis are not generally available in standard statistical software.

Campylobacter colonization in poultry: sources of infection and modes of transmission

Since its recognition as a human pathogen in the early 1970s, Campylobacter jejuni has now emerged as the leading bacterial cause of food-borne gastroenteritis in developed countries. Poultry, particularly chickens, account for the majority of human infections caused by Campylobacter. Reduction or elimination of this pathogen in the poultry reservoir is an essential step in minimizing the public health problem; however, farm-based intervention measures are still not available because of the lack of understanding of the ecological aspects of C. jejuni on poultry farms. Although Campylobacter is highly prevalent in poultry production systems, how poultry flocks become infected with this organism is still unknown. Many investigations indicate that horizontal transmission from environmental sources is the primary route of flock infections by Campylobacter. However, some recent studies also suggest the possibility of vertical transmission from breeder to progeny flocks. The transmission of the organism is not well understood, but it is likely to be through both vertical and horizontal transmission and may be affected by the immune status of the poultry host and the environmental conditions in the production system. Intervention strategies for Campylobacter infection in poultry should consider the complex nature of its transmission and may require the use of multiple approaches that target different segments of the poultry production system.

Survival of Ornithobacterium rhinotracheale in sterilized poultry litter

Ornithobacterium rhinotracheale (ORT) has been associated with respiratory disease, increased mortality, retarded growth, and decreased egg production in chickens and turkeys. Surveillance of exposure to ORT infection in the field has shown that prevalence of the infection is higher during winter months. The ability of ORT to remain viable in the poultry litter was studied at different temperatures over time. Presterilized poultry litter was inoculated with 10(11) colony-forming units of ORT and kept at -12 C, 4 C, 22 C, 37 C, and 42 C. Reisolation and titration of ORT from litter was attempted at intervals. Results indicate that ORT survived for 1 day at 37 C, 6 days at 22 C, 40 days at 4 C, and at least 150 days at -12 C. ORT did not survive 24 hr at 42 C. The survival of ORT at lower temperatures may be associated with the higher incidence of ORT infection in poultry during winter months.

Prevalence and antimicrobial susceptibility of thermophilic Campylobacter in organic and conventional broiler flocks

AIMS

To determine the flock prevalence and to estimate the within flock prevalence of Campylobacter in broiler flocks from different rearing systems, and to determine the antimicrobial susceptibility of Campylobacter isolates to selected antimicrobial substances.

METHODS AND RESULTS

One hundred and sixty broiler flocks originating from organic, conventional and extensive indoor production farms were investigated for the presence of Campylobacter at the time of slaughter. Campylobacter isolates from a subsample of positive flocks were subjected to susceptibility testing. Campylobacter spp. were isolated from 100% of organic broiler flocks, from 36.7% of conventional broiler flocks and from 49.2% of extensive indoor broiler flocks. Six of 62 Campylobacter isolates were resistant to one or more of the antimicrobials tested.

CONCLUSION

These results indicate that the special characteristics of organic broiler production provide a high prevalence of Campylobacter-positive flocks. Antimicrobial resistance was scarce among Campylobacter isolates from all rearing systems.

SIGNIFICANCE AND IMPACT OF THE STUDY

Organic broiler flocks constitute a strong potential for introduction of Campylobacter to the processing line upon arrival at slaughter.