Level Of Antimicrobial Use Research Articles

An economic assessment of alternative antimicrobial use scenarios on pig farms.

This paper explores the theoretical economic outcome of management changes that result in different levels of antimicrobial use (AMU) in two types of UK pig farm. A static farm economic pig production model (FEPM) was used on a representative 'Top-third' most profitable farm and a representative 'Mid-range' profitable farm. Three AMU theoretical management scenarios were investigated; (a) management changes leading to a reduction of AMU by 35% (AMU35); (b) more extensive management changes leading to a reduction of AMU by 95% (AMU95); and (c) implementing depopulation of the herd (AMU Depop). A sensitivity analysis was conducted to determine the effect of increases or decreases in pig revenue and feed price on farm gross margin under these scenarios. Over a single year, the AMU35 scenario was estimated to have a small positive impact (+3%) on both farm types. The other two AMU reduction scenarios had higher AMU reduction on farms but required higher variable cost and hence they resulted in lower farm profitability. There was a substantial reduction (up to -50%) in farm gross margin under these two AMU reduction scenarios in the modeled short-term time-period. The impact of the alternative AMU scenarios was slightly higher on a farm representing the 'Top-third' farm type, reducing farm gross margin further by 7% compared to the 'Mid-range' farm. Nevertheless, both farm types stay profitable under all three AMU scenarios. The results showed that in the modeled short-term implementing management changes that result in a reduction of on-farm AMU by 35% had a good economic outcome. In practice, the other two scenarios would be considered as longer-term strategies. Although both require higher initial costs to implement, the improved biosecurity and hygiene will benefit from lower disease occurrence for a longer term. Farm gross margins were, however, found to be highly sensitive to changes on market prices especially increasing feed prices. An increase of more than 15% in feed price moved a profitable farm into a loss-making farm. It will be economically challenging for uptakes of these, or similar, AMU reduction scenarios on farms if the market prices become un-favorable to pig farmers.

Prevalence and distribution of extended-spectrum β-lactamase and AmpC-producing Escherichia coli in two New Zealand dairy farm environments.

Antimicrobial resistance (AMR) is a global threat to human and animal health, with the misuse and overuse of antimicrobials being suggested as the main driver of resistance. In a global context, New Zealand (NZ) is a relatively low user of antimicrobials in animal production. However, the role antimicrobial usage on pasture-based dairy farms, such as those in NZ, plays in driving the spread of AMR within the dairy farm environment remains equivocal. Culture-based methods were used to determine the prevalence and distribution of extended-spectrum β-lactamase (ESBL)- and AmpC-producing Escherichia coli from farm environmental samples collected over a 15-month period from two NZ dairy farms with contrasting management practices. Whole genome sequencing was utilised to understand the genomic epidemiology and antimicrobial resistance gene repertoire of a subset of third-generation cephalosporin resistant E. coli isolated in this study. There was a low sample level prevalence of ESBL-producing E. coli (faeces 1.7%; farm dairy effluent, 6.7% from Dairy 4 and none from Dairy 1) but AmpC-producing E. coli were more frequently isolated across both farms (faeces 3.3% and 8.3%; farm dairy effluent 38.4%, 6.7% from Dairy 1 and Dairy 4, respectively). ESBL- and AmpC-producing E. coli were isolated from faeces and farm dairy effluent in spring and summer, during months with varying levels of antimicrobial use, but no ESBL- or AmpC-producing E. coli were isolated from bulk tank milk or soil from recently grazed paddocks. Hybrid assemblies using short- and long-read sequence data from a subset of ESBL- and AmpC-producing E. coli enabled the assembly and annotation of nine plasmids from six E. coli, including one plasmid co-harbouring 12 antimicrobial resistance genes. ESBL-producing E. coli were infrequently identified from faeces and farm dairy effluent on the two NZ dairy farms, suggesting they are present at a low prevalence on these farms. Plasmids harbouring several antimicrobial resistance genes were identified, and bacteria carrying such plasmids are a concern for both animal and public health. AMR is a burden for human, animal and environmental health and requires a holistic “One Health” approach to address.

Analysis of Antimicrobial Use and the Presence of Antimicrobial-Resistant Bacteria on Austrian Dairy Farms-A Pilot Study.

The assumed link between high levels of antimicrobial use on farms and selection for antimicrobial-resistant (AMR) bacteria on that farm remains difficult to prove. In the pilot study presented here, we analysed total antimicrobial use on 50 dairy farms in Austria and also collected environmental samples to ascertain whether specific AMR bacteria were present. Antimicrobial use (AMU) analysis was based on electronic veterinary treatment records over a one-year period. Faecal samples for the assessment of extended-spectrum beta-lactamase (ESBL)-producing E. coli were collected from cowsheds, calf pens, and youngstock housing areas, as well as dust samples from barns, to isolate methicillin-resistant Staphylococcus aureus (MRSA). Bacteriological cultures were carried out on selective agar. Farms were split into groups of 25 of the highest antimicrobial users and 25 of the lowest users. Overall, samples from 13/50 (26.0%) farms were found to be positive for the presence of ESBL-producing E. coli. Of these, eight farms were in the low user group and five were in the high user group. Only one farm was confirmed to harbour MRSA. Statistical analyses demonstrated that there was no significant difference in this study population between high or low antimicrobial use with respect to the presence of ESBL-producing E. coli on farms (p = 0.33). In conclusion, the presence of specific AMR bacteria on farms in this study population was not found to have a statistically proven relationship with their level of antimicrobial use.

Small-scale commercial chicken production: A risky business for farmers in the Mekong Delta of Vietnam

Small-scale farming of meat chicken flocks using local native breeds contributes to the economy of many rural livelihoods in Vietnam and many other low- and middle-income countries (LMICs). These systems are also the target of high levels of antimicrobial use (AMU); however, little is known about the profitability and sustainability of such systems. Since small-scale farms are commercial enterprises, this knowledge is essential to develop successful strategies to curb excessive AMU. Using longitudinal data from 203 small-scale (100−2,000 heads) native chicken flocks raised in 102 randomly selected farms in Dong Thap province (Mekong Delta, Vietnam), we investigated the financial and economic parameters of such systems and the main constraints to their sustainability. Feed accounted for the largest financial cost (flock median 49.5 % [Inter-quartile range (IQR) 41.5−61.8 %]) of total costs, followed by day-old-chicks (DOCs) (median 30.3 % [IQR 23.2−38.4 %]), non-antimicrobial health-supporting products (median 7.1 % [IQR 4.7−10.5 %]), vaccines (median 3.1 % [IQR 2.2−4.8 %]), equipment (median 1.9 % [IQR 0.0−4.9 %]) and antimicrobials (median 1.9 % [IQR 0.7−3.6 %]). Excluding labor costs, farmers achieved a positive return on investment (ROI) from 120 (59.1 %) flocks, the remainder generating a loss (median ROI 124 % [IQR 36–206 %]). Higher ROI was associated with higher flock size and low mortality. There was no statistical association between use of medicated feed and flock mortality or chicken bodyweight. The median daily income per person dedicated to raising chickens was 202,100 VND, lower than alternative rural labor activities in the Mekong Delta. In a large proportion of farms (33.4 %), farmers decided to stop raising chickens after completing one cycle. Farmers who dropped off chicken production purchased more expensive feed (in 1000 VND per kg): 11.1 [10.6−11.5] vs. 10.8 [10.4−11.3] for farms that continued production (p = 0.039), and experienced higher chicken mortality (28.5 % [12.0−79.0 %] vs. 16 [7.5−33.0 %]; p = 0.004). The rapid turnover of farmers raising chickens in such systems represents a challenge to the uptake of messages on appropriate AMU and chicken health. To ensure sustainability of small-scale commercial systems, advisory services need to be available to farmers as they initiate new flocks, and support them in the early stages to help overcome their limited experience and skills. This targeted approach would support profitability whilst reducing risk of emergence of AMR and infectious disease from these systems.

Irrational Use of Antimicrobials in Poultry Farms and Antimicrobial Resistance: A Cross-Sectional Study

Background: The rampant use of antimicrobials in poultry farms is creating a global public health threat as antimicrobial resistance (AMR) in humans may arise from such practice. This study was conducted with the objective of quantification and hence assessment of the level of antimicrobial use in Pakistani poultry farms so that appropriate utilization of such agents can be assured.
 Methods: Six randomly selected poultry farms of Pakistan with ten production cycles with 20,000- 30,000 birds in every production cycle were selected for the study from 2018 to 2019. The average dosage utilized on-farm was described by the defined daily dose (DDD) and used daily dose (UDD).
 Results: It was found that enrofloxacin, amoxicillin, doxycycline, tylocin, and lincomycin were the antimicrobials commonly used by all poultry farms. However, only Enrofloxacin (UDD/DDD = 0.95) was being used within the rational therapeutic range. All the antimicrobials were used irrationally without proper indication and suggestion by the veterinarian. No records on antimicrobials use were found on any farm. 
 Conclusion: The irrational use of antimicrobials in poultry farms may lead to antimicrobial resistance which has been a global public health threat. The speedy action should be implemented to discourage such rampant use of drugs in poultry farms in Pakistan and countries with similar farming practices for the effective use of antimicrobials in the proper indication.

Antibiotic use among surgical inpatients at a tertiary health facility: a case for a standardized protocol for presumptive antimicrobial therapy in the developing world

SummaryBackgroundIndiscriminate antimicrobial use is one of the greatest contributors to antimicrobial resistance. A low level of asepsis in hospitals and inadequate laboratory support have been adduced as reasons for indiscriminate use of antimicrobials among surgical patients. At present, there are no guidelines for presumptive antibiotic use in Nigeria and sub-Saharan Africa.AimSurgical inpatients at the study hospital were surveyed to determine the level of antimicrobial use and degree of compliance with prescription quality indicators.MethodsA cross-sectional survey was conducted among all surgical inpatients in May 2019 using a standardized tool developed by the University of Antwerp to assess the point prevalence of antimicrobials. Inpatients who were admitted from 08:00 h on the day of the survey were included. Data on patients' demographics, indication for antimicrobial use, reason for antimicrobial use, stop/review date, adherence to guidelines and laboratory use were collected. The prevalence of antimicrobial use in the surgical department was estimated.ResultsEighty-two inpatients were included in the survey. Of these, 97.6% were receiving at least one antimicrobial agent. Only 5.4% of the prescriptions were targeted, and 37.6% of prescriptions were for empirical treatment of infections. Approximately half (50.7%) of the patients were receiving presumptive antibiotics, and 6% were receiving prophylactic antibiotics. In total, 58.7% of prescriptions were administered parenterally, and 98.2% of patients had documentation of a stop/review date. Metronidazole (P=32.3%, T=29.2%), ceftriaxone (P=28.4%, T=19.8%) and ciprofloxacin (P=14.2%, T=14.6%) were the most common antimicrobials used.ConclusionsThere is a high rate of antimicrobial use among surgical inpatients, and the rate of indiscriminate antimicrobial prescribing among these patients needs to be reduced. This can be achieved by developing antimicrobial guidelines for presumptive antimicrobial therapy.

Veterinary Drug Shops as Main Sources of Supply and Advice on Antimicrobials for Animal Use in the Mekong Delta of Vietnam.

In the Mekong Delta of Vietnam, small-scale poultry farmers use large amounts of antimicrobials to raise their flocks, and veterinary drug shops owners and their staff are a key source of advice to farmers on antimicrobial use (AMU). We described the network of veterinary drug shops (n = 93) in two districts within Dong Thap province (Mekong Delta). We also interviewed a randomly selected sample of chicken farmers (n = 96) and described their linkages with veterinary drug shops. Antimicrobials represented 15.0% [inter quartile range (IQR) 6.0–25.0] of the shops’ income. Fifty-seven percent shop owners had been/were affiliated to the veterinary authority, 57% provided diagnostic services. The median number of drug shops supplying antimicrobials to each farm during one production cycle was 2 [IQR 1–2]. Visited shops were located within a median distance of 3.96 km [IQR 1.98–5.85] to farms. Drug shops owned by persons affiliated to the veterinary authority that did not provide diagnostic services had a higher fraction of their income consisting of antimicrobial sales (β = 1.913; p < 0.001). These results suggest that interventions targeting veterinary drug shop owners and their staff aiming at improving their knowledge base on livestock/poultry diseases and their diagnosis may contribute to reducing overall levels of AMU in the area.

Assessing the utility of leukocyte differential cell counts for predicting mortality risk in neonatal Holstein calves upon arrival and 72 hours postarrival at calf rearing facilities

There is growing concern about the level of antimicrobial use and antimicrobial resistance in food producing animals. An area of opportunity to reduce antimicrobial use could be in the treatment of young calves during the first week following arrival at calf rearing facilities. Group metaphylaxis is common due to the unknown age and history of calves that undergo several stressful events prior to arrival, such as transportation, co-mingling and variable periods of fasting. It may be possible to reduce antimicrobial use at this stage in the production cycle without sacrificing animal health and welfare if the calves at highest risk of morbidity and mortality could be identified and treated in a highly selective manner. Recent studies have identified indicators of future risk for morbidity and mortality that can be measured at arrival such as biomarkers and physical exam factors. Bovine haematology, when used in conjunction with clinical examination findings, could be used to improve disease diagnosis. The objective of this study was to assess the utility of leukocyte differential cell counts taken at the time of arrival at a calf rearing facility and 72 hours post arrival for determining mortality risk during the production cycle.

High-Resolution Monitoring of Antimicrobial Consumption in Vietnamese Small-Scale Chicken Farms Highlights Discrepancies Between Study Metrics.

Chicken is, among farmed species, the target of the highest levels of antimicrobial use (AMU). There are considerable knowledge gaps on how and when antimicrobials are used in commercial small-scale chicken farms. These shortcomings arise from cross-sectional study designs and poor record keeping practiced by many such farmers. Furthermore, there is a large diversity of AMU metrics, and it is not clear how these metrics relate to each other. We performed a longitudinal study on a cohort of small-scale chicken farms (n = 102) in the Mekong Delta (Vietnam), an area regarded as a hotspot of AMU, from October 2016 to May 2018. We collected data on all medicine products administered to 203 flocks with the following aims: (1) to describe types and quantities of antimicrobial active ingredients (AAIs) used; (2) to describe critical time points of AMU; and (3) to compare AMU using three quantitative metrics: (a) weight of AAIs related to bird weight at the time of treatment (mg/kg at treatment); (b) weight of AAIs related to weight of birds sold (mg/kg sold); and (c) “treatment incidence” (TI), or the number of daily doses per kilogram of live chicken [Vietnamese animal daily dose (ADDvetVN)] per 1,000 days. Antimicrobials contained in commercial feed, administered by injection (n = N = 6), or antimicrobials for human medicine (n = N = 16) were excluded. A total of 236 products were identified, containing 42 different AAIs. A total of 76.2% products contained AAIs of “critical importance” according to the World Health Organization (WHO). On average, chickens consumed 791.8 (SEM ±16.7) mg/kg at treatment, 323.4 (SEM ±11.3) mg/kg sold, and the TI was 382.6 (SEM ±5.5) per 1,000 days. AMU was more common early in the production cycle and was highly skewed, with the upper 25% quantile of flocks accounting for 60.7% of total AMU. The observed discrepancies between weight- and dose-based metrics were explained by differences in the strength of AAIs, mortality levels, and the timing of administration. Results suggest that in small-scale chicken production, AMU reduction efforts should preferentially target the early (brooding) period, which is when birds are most likely to be exposed to antimicrobials, whilst restricting access to antimicrobials of critical importance for human medicine.

An epidemiological analysis of the level of biosecurity and animal welfare on pig farms in Japan and their effect on the use of veterinary antimicrobials.

In Japan the highest use of veterinary antimicrobials is in pig production. To obtain useful information to achieve the best approach to reducing this use, we analyzed the association between the level of on-farm biosecurity and animal welfare with the level of antimicrobial use as recorded on prescriptions on 38 pig farms under contract to veterinarians of the Japanese Association of Swine Veterinarians. To determine the level of welfare we recorded the risk of pre- and post-weaning deaths and the floor space available per fattening pig (m2/head). Multivariable linear regression analysis was performed, using biosecurity scores and animal welfare indicators as independent variables and the amount of antimicrobial usage as dependent variables. The results showed that the higher scores for the site condition (location) and external biosecurity scores of the sub-categories ‘farm contractors’ were strongly associated with the lower use of oral antimicrobials (P<0.05). This suggests that in order to reduce the usage of antimicrobials for herd treatments, farmers should consider the location when building a new farm or pig house and strengthen the entrance requirements for high risk visitors. Regression analysis for the respective antimicrobials showed that the site condition, the biosecurity scores of the sub-categories ‘farm contractors’, ‘pen layouts’ (e.g. independence of pens and sites), ‘pig flows’ (e.g. the completeness of all-in/ all-out system) and an animal welfare indicator (i.e. post-weaning mortality risk) were significantly associated with the use of one or more antimicrobials (P<0.05).

Use of Colistin and Other Critical Antimicrobials on Pig and Chicken Farms in Southern Vietnam and Its Association with Resistance in Commensal Escherichia coli Bacteria.

ABSTRACTAntimicrobial resistance (AMR) is a global health problem, and emerging semi-intensive farming systems in Southeast Asia are major contributors to the AMR burden. We accessed 12 pig and chicken farms at key stages of production in Tien Giang Province, Vietnam, to measure antimicrobial usage and to investigate the prevalence of AMR to five critical antimicrobials (β-lactams, third-generation cephalosporins, quinolones, aminoglycosides, and polymyxins) and their corresponding molecular mechanisms among 180 Escherichia coli isolates. Overall, 94.7 mg (interquartile range [IQR], 65.3 to 151.1) and 563.6 mg (IQR, 398.9 to 943.6) of antimicrobials was used to produce 1 kg (live weight) of chicken and pig, respectively. A median of 3 (out of 8) critical antimicrobials were used on pig farms. E. coli isolates exhibited a high prevalence of resistance to ampicillin (97.8% and 94.4% for chickens and pigs, respectively), ciprofloxacin (73.3% and 21.1%), gentamicin (42.2% and 35.6%), and colistin (22.2% and 24.4%). The prevalence of a recently discovered colistin resistance gene, mcr-1, was 19 to 22% and had strong agreement with phenotypic colistin resistance. We conducted plasmid conjugation experiments with 37 mcr-1 gene-positive E. coli isolates and successfully observed transfer of the gene in 54.0% of isolates through a plasmid of approximately 63 kb, consistent with one recently identified in China. We found no significant correlation between total use of antimicrobials at the farm level and AMR. These data provide additional insight into the role of mcr-1 in colistin resistance on farms and outline the dynamics of phenotypic and genotypic AMR in semi-intensive farming systems in Vietnam.IMPORTANCE Our study provides accurate baseline information on levels of antimicrobial use, as well as on the dynamics of phenotypic and genotypic resistance for antimicrobials of critical importance among E. coli over the different stages of production in emerging pig and poultry production systems in Vietnam. E. coli isolates showed a high prevalence of resistance (>20%) to critically important antimicrobials, such as colistin, ciprofloxacin, and gentamicin. The underlying genetic mechanisms identified for colistin (the mcr-1 gene) and quinolone (gyrA gene mutations) are likely to play a major role in AMR to those compounds. Conjugation experiments led to the identification of a 63-kb plasmid, similar to one recently identified in China, as the potential carrier of the mcr-1 gene. These results should encourage greater restrictions of such antimicrobials in Southeast Asian farming systems.

Declines in Outpatient Antimicrobial Use in Canada (1995–2010)

BackgroundWith rising reports of antimicrobial resistance in outpatient communities, surveillance of antimicrobial use is imperative for supporting stewardship programs. The primary objective of this article is to assess the levels of antimicrobial use in Canada over time.MethodsCanadian antimicrobial use data from 1995 to 2010 were acquired and assessed by four metrics: population-adjusted prescriptions, Defined Daily Doses, spending on antimicrobials (inflation-adjusted), and average Defined Daily Doses per prescription. Linear mixed models were built to assess significant differences among years and antimicrobial groups, and to account for repeated measurements over time. Measures were also compared to published reports from European countries.ResultsTemporal trends in antimicrobial use in Canada vary by metric and antimicrobial grouping. Overall reductions were seen for inflation-adjusted spending, population-adjusted prescription rates and Defined Daily Doses, and increases were observed for the average number of Defined Daily Doses per prescription. The population-adjusted prescription and Defined Daily Doses values for 2009 were comparable to those reported by many European countries, while the average Defined Daily Dose per prescription for Canada ranked high. A significant reduction in the use of broad spectrum penicillins occurred between 1995 and 2004, coupled with increases in macrolide and quinolone use, suggesting that replacement of antimicrobial drugs may occur as new products arrive on the market.ConclusionsThere have been modest decreases of antimicrobial use in Canada over the past 15 years. However, continued surveillance of antimicrobial use coupled with data detailing antimicrobial resistance within bacterial pathogens affecting human populations is critical for targeting interventions and maintaining the effectiveness of these products for future generations.

Antimicrobial Resistance Trends AmongSalmonellaIsolates Obtained from Dairy Cattle in the Northeastern United States, 2004–2011

Monitoring antimicrobial resistance trends among bacteria isolated from food animals and people is necessary to inform public policy regarding appropriate antimicrobial use. Our objectives were to describe the antimicrobial resistance status of Salmonella isolates from dairy cattle in the northeastern United States and to identify trends in resistance to various antimicrobial agents over time. Data were collected retrospectively for all bovine Salmonella isolates that were obtained from samples submitted to Cornell University's Animal Health Diagnostic Center between January 1, 2004 and December 31, 2011. Temporal trends in the prevalence of resistant Salmonella were investigated for each antimicrobial agent using the Cochran-Armitage trend test. Antimicrobial susceptibility testing was performed on 2745 bovine Salmonella isolates from clinical samples submitted during the study period. Overall resistance to each antimicrobial agent ranged from 0% (amikacin, ciprofloxacin, and nalidixic acid) to 72.0% (sulfadimethoxine). There was evidence of a significantly decreasing trend in prevalence of resistance to most agents: amoxicillin/clavulanic acid (AUG), ampicillin (AMP), cefoxitin (FOX), ceftiofur (TIO), ceftriaxone (AXO), chloramphenicol (CHL), chlortetracycline (CTET), florfenicol (FFN), kanamycin (KAN), neomycin (NEO), oxytetracycline (OXY), spectinomycin (SPE), streptomycin (STR), sulfadimethoxine (SDM), sulfisoxazole (FIS), and tetracycline (TET). Among the 265 isolates that were tested using the National Antimicrobial Resistance Monitoring System (NARMS) panel, the most common resistance patterns were pansusceptible (54.0%), AUG-AMP-FOX-TIO-AXO-CHL-KAN-STR-FIS-TET (18.1%), and AUG-AMP-FOX-TIO-AXO-CHL-STR-FIS-TET (12.1%). Increasing prevalence of S. enterica serovar Cerro over the course of the study period presumably had an impact on the observed resistance trends. Nevertheless, these results do not support the notion that the current level of antimicrobial use in dairy cattle is driving an increase in the emergence and dissemination of drug-resistant Salmonella in the region served by the laboratory.

Molecular Epidemiology of Methicillin-Resistant Staphylococcus aureus Isolated from Children in a Community with Low Antimicrobial Pressure in Japan

Sado Island in Japan is an area with low antimicrobial pressure. A total of 41 community-onset methicillin-resistant Staphylococcus aureus (MRSA) isolates were obtained from pediatric outpatients and healthy children between August 2009 and January 2012, and genotyping and antimicrobial susceptibility testing of the MRSA isolates were performed. Additionally, the sources of MRSA isolated from healthy 1-month-old neonates were assessed. All isolates were negative for the Panton-Valentine leukocidin genes. Our data showed a lower prevalence of staphylococcal cassette chromosome (SCC)mecII on Sado Island (31.7% in total and 46.7% in healthy carriage) than that in the other areas of Japan, suggesting that a low level of antimicrobial use may be related to a low SCCmecII carriage rate in the community. To our knowledge, this is the first report of sequence type (ST)81/SCCmecIVg strains as well as the novel ST strain (ST2180/SCCmecIVa) in Japan. In addition, we detected an arginine catabolic mobile element (ACME)-arcA-positive ST764/SCCmecIIa clone that could disseminate successfully in the community. Intrafamilial transmission was observed in neonates identified with the SCCmecIV MRSA strains, and these strains were genetically typed as community-associated MRSA; the transmission routes of the remaining SCCmecIIa MRSA (genetically typed as healthcare-associated MRSA) strains could not be defined. In this study, we have shown that multiple MRSA strains can circulate in a community even under low antimicrobial pressure.

Prevalence and Antimicrobial Resistance of Campylobacter in Antimicrobial-Free and Conventional Pig Production Systems

The objectives of this study were to determine and compare the prevalence and antimicrobial resistance of Campylobacter species in swine reared in conventional and antimicrobial-free (ABF) production systems. Campylobacter coli was the predominant species, with 1,459 isolates (99%) in the study. We found significantly higher prevalence of C. coli on the ABF farms (77.3%) than on the conventional farms (27.6%) among pigs at the nursery stage (P < 0.001). At slaughter, we found significantly higher prevalence at the postevisceration than at the preevisceration stage (P < 0.001) in both production systems. The 1,459 C. coli isolates were tested with the agar dilution method for their susceptibility to six antimicrobials: chloramphenicol, ciprofloxacin, erythromycin, gentamicin, nalidixic acid, and tetracycline. Resistance was most prevalent against tetracycline (66.2% of isolates) followed by erythromycin (53.6% of isolates). Frequency of resistance to these two antimicrobials was significantly higher among conventional herds (83.4% for tetracycline and 77% for erythromycin) than among ABF herds (56.2% for tetracycline and 34.5% for erythromycin). Resistance to ciprofloxacin at the MIC (>4 mg/liter) was also found on farms in both systems. Multidrug-resistant C. coli strains were detected in both the conventional (7%) and ABF (4%) herds. This is the first report of ciprofloxacin-resistant strains of C. coli in ABF pigs in the United States. These findings highlight the high prevalence of antimicrobial-resistant C. coli in both conventional and ABF pig production systems and have significant implications for the persistence of antimicrobial-resistant Campylobacter in the pig production environment regardless of levels of antimicrobial use.

Stakeholder position paper: Epidemiological perspectives on antibiotic use in animals

Epidemiologists studying antimicrobial resistance are often interested in analyzing the association between antimicrobial resistance and antimicrobial use in animals, and on the impact of antimicrobial use in animals on the occurrence of resistance in bacteria affecting human populations. Given the various potential antimicrobial use data sources, it seems likely there will be some variability in the utility of the data for interpreting trends in antimicrobial resistance and investigating the relationship between antimicrobial use in animals and antimicrobial resistance in bacteria affecting human health. From an epidemiologic perspective, the major issues related to incorporation of antimicrobial use data into antimicrobial resistance monitoring programs are the further development of epidemiologic methods for collecting, quantifying, analyzing and interpreting use data; an open and realistic consideration of the limitations of the data; developing an understanding of scaling, temporal and spatial heterogeneity issues; and the interpretative problems of ecologic and atomistic fallacy. Given the many potential biases in antimicrobial use data, attempts to relate levels of antimicrobial use to levels of antimicrobial resistance should be done with caution until the data are better understood and the aforementioned issues have been addressed.

A pharmaco-epidemiological analysis of factors associated with antimicrobial consumption level in turkey broiler flocks

An on-farm pharmaco-epidemiological survey of 246 turkey broiler flocks from 131 farms was carried out to assess the homogeneity of antimicrobial use between flocks on the same farm and to explore the possible relationships between farm and farmer characteristics and the level of antimicrobial use. The antimicrobial use in each flock was quantified by an invoice study, expressed as the number of national animal daily doses (ADD)/turkey broiler and characterised as "high", "medium" or "low" according to the tertiles of the resulting distribution. Antimicrobial use was then correlated with variables collected from the farmer by means of an alternating logistic regression method which calculates the pairwise odds ratio (PWOR) for within-farm clustering. Two independent models were fitted: (1) "low" versus "medium" + "high" antimicrobial consumption and (2) "high" versus "medium" + "low" antimicrobial consumption. PWOR from the null models were significant (P < 0.005), but only remained significant in the first final model (P = 0.002). Four explanatory variables were retained for both models. Prophylactic antimicrobial administration and veterinarian antimicrobial prescription attaining the farm technical staff's expectation were associated with a higher antimicrobial consumption level. Administration of competitive exclusion flora and compliance with biosecurity rules of changing clothes and shoes before entering the facilities, were associated with a lower antimicrobial consumption level. In the first model, the number of full-time jobs devoted to the turkey production unit (1 versus more than 1) was also found to be associated with the antimicrobial consumption level. The study tends to confirm the feasibility of the adopted approach to quantify antimicrobial use and to determine the factors likely to influence antimicrobial consumption.

The effect of antimicrobial growth promoter withdrawal on the health of weaned pigs in Finland

The use of the antimicrobial growth promoters (AGPs) carbadox and olaquindox has been banned in the European Union (EU) since September 1999. We studied the effects of the withdrawal on the health of weaned piglets on two types of piglet-producing farms (farrowing herds and farrow-to-finish herds) from the different regions of Finland. Farms with no major problems with post-weaning diarrhoea were selected for the study to better evaluate the effect of AGPs alone. Data on production, medication and incidence of diarrhoea were collected from 73 farms during 1 year after the withdrawal. On 29 of these farms, the data collection began 4 months before the withdrawal. The health management of the pigs is considered good in Finland, and special attention has been paid to improve the husbandry practices and management of the farms. Eighty-two percent of the farms in the study were free of both Mycoplasma hyopneumoniae and Sarcoptes scabiei infection. Brachyspira hyodysenteriae infection was not detected in any of the farms. The median number of sows in the herds was 56.0 (IQR = 43.0; 72.5) in 2000. The level of antimicrobial use in each herd was classified as low, moderate and high when the percentage of weaned pigs treated for diarrhoea during a 4-month period was 0–5%, 6–19% and ≥20%, respectively. Only on four herds (14%), there was an increase in the level of antibiotic use after the AGP withdrawal, when seasonally corresponding 4-month periods were compared. Fourty-one percent of these 29 farms were categorized as low users of antimicrobials, 38% as moderate users and 21% as high users. The level of antimicrobial use for treatment of diarrhoea after weaning (and the incidence of diarrhoea in weaned piglets) did not increase significantly after the withdrawal of AGPs from weaner feeds according to farmers’ evaluations. In this study, the Escherichia coli infection was the most-common cause of diarrhoea in weaned pigs. The age at weaning did not change after the withdrawal of AGPs.