Modelling and forecasting antimicrobial resistance and its dynamic relationship to antimicrobial use: a time series analysis

Studying the time trend of Methicillin-resistant Staphylococcus aureus (MRSA) in Norway by use of non-stationary γ-Poisson distributions

OBJECTIVES

Study the time development of methicillin-resistant Staphylococcus aureus (MRSA) and forecast future behaviour. The major question: Is the number of MRSA isolates in Norway increasing and will it continue to increase?

DESIGN

Time trend analysis using non-stationary γ-Poisson distributions.

SETTING

Two data sets were analysed. The first data set (data set I) consists of all MRSA isolates collected in Oslo County from 1997 to 2010; the study area includes the Norwegian capital of Oslo and nearby surrounding areas, covering approximately 11% of the Norwegian population. The second data set (data set II) consists of all MRSA isolates collected in Health Region East from 2002 to 2011. Health Region East consists of Oslo County and four neighbouring counties, and is the most populated area of Norway.

PARTICIPANTS

Both data sets I and II consist of all persons in the area and time period described in the Settings, from whom MRSA have been isolated.

PRIMARY AND SECONDARY OUTCOME MEASURES

MRSA infections have been mandatory notifiable in Norway since 1995, and MRSA colonisation since 2004. In the time period studied, all bacterial samples in Norway have been sent to a medical microbiological laboratory at the regional hospital for testing. In collaboration with the regional hospitals in five counties, we have collected all MRSA findings in the South-Eastern part of Norway over long time periods.

RESULTS

On an average, a linear or exponential increase in MRSA numbers was observed in the data sets. A Poisson process with increasing intensity did not capture the dispersion of the time series, but a γ-Poisson process showed good agreement and captured the overdispersion. The numerical model showed numerical internal consistency.

CONCLUSIONS

In the present study, we find that the number of MRSA isolates is increasing in the most populated area of Norway during the time period studied. We also forecast a continuous increase until the year 2017.

Forecasting carbapenem resistance from antimicrobial consumption surveillance: Lessons learnt from an OXA-48-producing Klebsiella pneumoniae outbreak in a West London renal unit

This study aimed to forecast the incidence rate of carbapenem resistance and to assess the impact of an antimicrobial stewardship intervention using routine antimicrobial consumption surveillance data. Following an outbreak of OXA-48-producing Klebsiella pneumoniae (January 2008-April 2010) in a renal cohort in London, a forecasting ARIMA model was derived using meropenem consumption data [defined daily dose per 100 occupied bed-days (DDD/100OBD)] from 2005-2014 as a predictor of the incidence rate of OXA-48-producing organisms (number of new cases/year/100,000OBD). Interrupted times series assessed the impact of meropenem consumption restriction as part of the outbreak control. Meropenem consumption at lag -1 year (the preceding year), highly correlated with the incidence of OXA-48-producing organisms (r=0.71; P=0.005), was included as a predictor within the forecasting model. The number of cases/100,000OBD for 2014-2015 was estimated to be 4.96 (95% CI 2.53-7.39). Analysis of meropenem consumption pre- and post-intervention demonstrated an increase of 7.12 DDD/100OBD/year (95% CI 2.97-11.27; P<0.001) in the 4 years preceding the intervention, but a decrease thereafter. The change in slope was -9.11 DDD/100OBD/year (95% CI -13.82 to -4.39). Analysis of alternative antimicrobials showed a significant increase in amikacin consumption post-intervention from 0.54 to 3.41 DDD/100OBD/year (slope +0.72, 95% CI 0.29-1.15; P=0.01). Total antimicrobials significantly decreased from 176.21 to 126.24 DDD/100OBD/year (P=0.05). Surveillance of routinely collected antimicrobial consumption data may provide a key warning indicator to anticipate increased incidence of carbapenem-resistant organisms. Further validation using real-time data is needed.

Influence of antimicrobial consumption on gram-negative bacteria in inpatients receiving antimicrobial resistance therapy from 2008-2013 at a tertiary hospital in Shanghai, China

BACKGROUND

Irrational use of antimicrobial agents is a major cause of increased antimicrobial resistance. Effective antibiotic stewardship strategies nationwide or in local health care settings are necessary to reduce antibiotic use and bacteria resistance.

METHODS

We evaluated the effectiveness of China's antimicrobial stewardship policy on antimicrobial use and applied time-series analysis methodology to determine the temporal relationship between antibiotic use and gram-negative bacteria resistance at Changhai Hospital from 2008-2013. Isolates investigated included Escherichia coli, Klebsiella pneumoniae, Acinetobacter baumannii, and Pseudomonas aeruginosa.

RESULTS

Consumption of 7 restricted-use antibiotics was dramatically reduced. Resistance to ceftazidime in P aeruginosa and A baumannii and resistance to ciprofloxacin in P aeruginosa significantly decreased. By using cross-correlation analysis, associations between ciprofloxacin resistance in P aeruginosa and fluoroquinolones consumption (r = 0.48; lag = 0; P = .02), ceftazidime resistance in P aeruginosa and third-generation cephalosporins consumption (r = 0.54; lag = -1; P = .01) were identified. No substantial association between other pairs was found.

CONCLUSIONS

Enhanced nationwide antimicrobial stewardship campaigns launched in 2011 have made great achievements in regard to antibiotic use but have had limited effects on the reversal of gram-negative bacteria resistance in health care settings. Sound infection prevention and control programs to reduce the transmission of resistant pathogens for hospitals in China are urgently needed.

Turning the tide or riding the waves? Impacts of antibiotic stewardship and infection control on MRSA strain dynamics in a Scottish region over 16 years: non-linear time series analysis

OBJECTIVES

To explore temporal associations between planned antibiotic stewardship and infection control interventions and the molecular epidemiology of methicillin-resistant Staphylococcus aureus (MRSA).

DESIGN

Retrospective ecological study and time-series analysis integrating typing data from the Scottish MRSA reference laboratory.

SETTING

Regional hospital and primary care in a Scottish Health Board.

PARTICIPANTS

General adult (N=1,051,993) or intensive care (18,235) admissions and primary care registrations (460,000 inhabitants) between January 1997 and December 2012.

INTERVENTIONS

Hand-hygiene campaign; MRSA admission screening; antibiotic stewardship limiting use of macrolides and '4Cs' (cephalosporins, coamoxiclav, clindamycin and fluoroquinolones).

OUTCOME MEASURES

Prevalence density of MRSA clonal complexes CC22, CC30 and CC5/Other in hospital (isolates/1000 occupied bed days, OBDs) and community (isolates/10,000 inhabitant-days).

RESULTS

67% of all clinical MRSA isolates (10,707/15,947) were typed. Regional MRSA population structure was dominated by hospital epidemic strains CC30, CC22 and CC45. Following declines in overall MRSA prevalence density, CC5 and other strains of community origin became increasingly important. Reductions in use of '4Cs' and macrolides anticipated declines in sublineages with higher levels of associated resistances. In multivariate time-series models (R(2)=0.63-0.94) introduction of the hand-hygiene campaign, reductions in mean length of stay (when >4 days) and bed occupancy (when >74 to 78%) predicted declines in CC22 and CC30, but not CC5/other strains. Lower importation pressures, expanded MRSA admission screening, and reductions in macrolide and third generation cephalosporin use (thresholds for association: 135-141, and 48-81 defined daily doses/1000 OBDs, respectively) were followed by declines in all clonal complexes. Strain-specific associations with fluoroquinolones and clindamycin reflected resistance phenotypes of clonal complexes.

CONCLUSIONS

Infection control measures and changes in population antibiotic use were important predictors of MRSA strain dynamics in our region. Strategies to control MRSA should consider thresholds for effects and strain-specific impacts.

Association between Clostridium difficile infection and antimicrobial usage in a large group of English hospitals

AIMS

This study aimed to determine the association between the reduction in the number of Clostridium difficile infection (CDI) cases reported by the English National Health Service (NHS) hospitals and concurrent antimicrobial use.

METHODS

A retrospective ecological study for January 2005 to December 2008 was conducted using data from 26 of the 29 NHS trusts (i.e. a trust manages one or more hospitals) located in the North West Strategic Health Authority of England. Antimicrobial use data, for patients of all ages, were provided by IMS Health, and CDI case data for patients aged ≥65 years were provided by the Health Protection Agency. Antimicrobial use was converted into defined daily doses (DDDs). The overall association between antimicrobial use and CDI for the trusts was investigated using multilevel models.

RESULTS

Our study shows a positive significant association between the CDI cases and the use of the following antimicrobials: ‘third-generation cephalosporins’ [11.62 CDI cases per 1000 DDDs; 95% confidence interval (CI), 5.92–17.31]; ‘fluoroquinolones’ (4.79 CDI cases per 1000 DDDs; 95% CI, 2.83–6.74); and ‘second-generation cephalosporins’ (4.25 CDI cases per 1000 DDDs; 95% CI, 1.66–6.83). The strength of this association was not significantly different (95% CI) among the antimicrobial groups.

CONCLUSIONS

This study shows that the reduction in the number of CDI cases reported by the English NHS hospitals is associated with concurrent reductions in antimicrobial use. This means that the number of CDI cases over time decreased in a similar fashion to the usage of various antimicrobials.

Attributable Cost and Length of Stay for Patients With Central Venous Catheter—Associated Bloodstream Infection in Mexico City Intensive Care Units A Prospective, Matched Analysis

Background.

No information is available about the financial impact of central venous catheter (CVC)-associated bloodstream infection (BSI) in Mexico.

Objective.

To calculate the costs associated with BSI in intensive care units (ICUs) in Mexico City.

Design.

An 18-month (June 2002 through November 2003), prospective, nested case-control study of patients with and patients without BSI.

Setting.

Adult ICUs in 3 hospitals in Mexico City.

Patients and Methods.

A total of 55 patients with BSI (case patients) and 55 patients without BSI (control patients) were compared with respect to hospital, type of ICU, year of hospital admission, length of ICU stay, sex, age, and mean severity of illness score. Information about the length of ICU stay was obtained prospectively during daily rounds. The daily cost of ICU stay was provided by the finance department of each hospital. The cost of antibiotics prescribed for BSI was provided by the hospitals' pharmacy departments.

Results.

For case patients, the mean extra length of stay was 6.1 days, the mean extra cost of antibiotics was $598, the mean extra hospital cost was $11,591, and the attributable extra mortality was 20%.

Conclusions.

In this study, the duration of ICU stay for patients with central venous catheter-associated BSI was significantly longer than that for control patients, resulting in increased healthcare costs and a higher attributable mortality. These conclusions support the need to implement preventive measures for hospitalized patients with central venous catheters in Mexico.

Time-Series Analysis of the Impact of Bed Occupancy Rates on the Incidence of Methicillin-Resistant Staphylococcus aureus Infection in Overcrowded General Wards

Objective.

We investigated the impact of bed occupancy, particularly overcrowding, on the incidence of methicillin-resistant Staphylococcus aureus (MRSA) infection in general ward settings.

Methods.

We performed a time-series and mixed-model analysis of variance of monthly incidence of MRSA infection and corresponding bed occupancy rates, over 65 months, in the medicine and surgical wards within St. Luke's Hospital, a 900-bed tertiary care facility in Malta.

Results.

In the medicine wards, significant periodic fluctuations in bed demand were evident during the study period, with peaks of occupancy greater than 120% during the winter months. Cross-correlation analysis between the rate of bed occupancy and the rate of MRSA infection displayed an oscillatory configuration, with a periodicity of 12, similar to the periodicity evident in the autocorrelation bed-occupancy pattern. Further statistical analysis by means of analysis of variance confirmed that the months with excessive overcrowding tended to coincide with a significant increase in the rate of MRSA infection, occurring after a lag of approximately 2 months. Identical analysis of equivalent data from the surgical wards also revealed significant fluctuation in the rate of bed occupancy; however, occupancy never exceeded 100%. No cross-correlational relationship with MRSA infection incidence was present.

Conclusion.

The study data suggest that, in our setting, simple fluctuations in the rate of bed occupancy did not have a direct impact on the incidence of MRSA infection as long as the rate of bed occupancy was within designated levels. Rather, it was episodes of significant overcrowding, with occupancy levels in excess of designated numbers, that triggered increases in infection incidence rates.

Forecasting ESKAPE infections through a time-varying auto-adaptive algorithm using laboratory-based surveillance data

Background

Mathematical or statistical tools are capable to provide a valid help to improve surveillance systems for healthcare and non-healthcare-associated bacterial infections. The aim of this work is to evaluate the time-varying auto-adaptive (TVA) algorithm-based use of clinical microbiology laboratory database to forecast medically important drug-resistant bacterial infections.

Methods

Using TVA algorithm, six distinct time series were modelled, each one representing the number of episodes per single ‘ESKAPE’ (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter species) infecting pathogen, that had occurred monthly between 2002 and 2011 calendar years at the Università Cattolica del Sacro Cuore general hospital.

Results

Monthly moving averaged numbers of observed and forecasted ESKAPE infectious episodes were found to show a complete overlapping of their respective smoothed time series curves. Overall good forecast accuracy was observed, with percentages ranging from 82.14% for E. faecium infections to 90.36% for S. aureus infections.

Conclusions

Our approach may regularly provide physicians with forecasted bacterial infection rates to alert them about the spread of antibiotic-resistant bacterial species, especially when clinical microbiological results of patients’ specimens are delayed.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-014-0634-9) contains supplementary material, which is available to authorized users.

Increases of antibiotic resistance in excessive use of antibiotics in smallholder dairy farms in northern Thailand

Antibiotic resistance patterns of bacterial isolates from both quarter teat-tip swabs and their quarter milk samples were evaluated in smallholder dairy farms in northern Thailand with excessive use of antibiotics (HIGH) compared with normal use (NORM). Results from teat-tip swab samples showed that the percentage of Bacillus spp. resistance to overall antibiotics was significantly lower in the NORM group than that of the HIGH group, whereas, the resistance percentage of coagulase-negative staphylococci in the NORM group was higher than that of the HIGH one. The overall mastitis-causing bacteria isolated from milk samples were environmental streptococci (13.8%), coagulase-negative staphylococci (9.9%), Staphylococcus aureus (5.4%), and Corynebacterium bovis (4.5%). Both staphylococci and streptococci had significantly higher percentages of resistance to cloxacillin and oxacillin in the HIGH group when compared to the NORM one. An occurrence of vancomycin-resistant bacteria was also observed in the HIGH group. In conclusion, the smallholder dairy farms with excessive use of antibiotics had a higher probability of antibiotic-resistant pattern than the farms with normal use.

Access, excess, and ethics--towards a sustainable distribution model for antibiotics

The increasing antibiotic resistance is a global threat to health care as we know it. Yet there is no model of distribution ready for a new antibiotic that balances access against excessive or inappropriate use in rural settings in low- and middle-income countries (LMICs) where the burden of communicable diseases is high and access to quality health care is low. Departing from a hypothetical scenario of rising antibiotic resistance among pneumococci, 11 stakeholders in the health systems of various LMICs were interviewed one-on-one to give their view on how a new effective antibiotic should be distributed to balance access against the risk of inappropriate use. Transcripts were subjected to qualitative 'framework' analysis. The analysis resulted in four main themes: Barriers to rational access to antibiotics; balancing access and excess; learning from other communicable diseases; and a system-wide intervention. The tension between access to antibiotics and rational use stems from shortcomings found in the health systems of LMICs. Constructing a sustainable yet accessible model of antibiotic distribution for LMICs is a task of health system-wide proportions, which is why we strongly suggest using systems thinking in future research on this issue.

Antibiotic resistance in pediatric urology

Antibiotics are a mainstay in the treatment of bacterial infections, though their use is a primary risk factor for the development of antibiotic resistance. Antibiotic resistance is a growing problem in pediatric urology as demonstrated by increased uropathogen resistance. Lack of urine testing, nonselective use of prophylaxis, and poor empiric prescribing practices exacerbate this problem. This article reviews antibiotic utilization in pediatric urology with emphasis on modifiable practice patterns to potentially help mitigate the growing rates of antibiotic resistance. This includes urine testing to only treat when indicated and tailor broad-spectrum therapy as able; selective application of antibiotic prophylaxis to patients with high-grade vesicoureteral reflux and hydronephrosis with counseling regarding the importance of compliance; and using local antiobiograms, particularly pediatric-specific antiobiograms, with inpatient versus outpatient data.

Disease management with ARIMA model in time series

The evaluation of infectious and noninfectious disease management can be done through the use of a time series analysis. In this study, we expect to measure the results and prevent intervention effects on the disease. Clinical studies have benefited from the use of these techniques, particularly for the wide applicability of the ARIMA model. This study briefly presents the process of using the ARIMA model. This analytical tool offers a great contribution for researchers and healthcare managers in the evaluation of healthcare interventions in specific populations.

Correlation between veterinary antimicrobial use and antimicrobial resistance in food-producing animals: a report on seven countries

OBJECTIVES

To evaluate correlations between antimicrobial use and the prevalence of resistance in commensal Escherichia coli isolates from pigs, poultry and cattle, using data from publicly available national or international reports from seven European countries.

METHODS

The link between the quantities of different classes of antimicrobials administered to food-producing animals per country (expressed in mg/population correction unit) and the prevalence of resistance to the different antimicrobial classes (interpreted by EUCAST epidemiological cut-off values) in E. coli isolates (4831 isolates in total) was assessed by means of polynomial regression analysis and determination of Spearman's rank correlation coefficient.

RESULTS

A quadratic regression best fitted the antimicrobial use and antimicrobial resistance data. The coefficient of determination was, in decreasing order, 0.99 for fluoroquinolones and amphenicols, 0.94 for third-generation cephalosporins and sulphonamides, 0.93 for aminopenicillins, 0.86 for fluoroquinolones, 0.81 for streptomycin and 0.80 for gentamicin and tetracycline. Spearman's rank correlation coefficient was 1 for amphenicols, 0.96 for sulphonamides, 0.93 for streptomycin and tetracycline, 0.89 for aminopenicillins, 0.71 for gentamicin and 0.70 for third-generation cephalosporins.

CONCLUSIONS

These remarkably high coefficients indicate that, at a national level, the level of use of specific antimicrobials strongly correlates to the level of resistance towards these agents in commensal E. coli isolates in pigs, poultry and cattle. However, data restraints reveal the need for further detail in collection and harmonization of antimicrobial resistance and use data in Europe.

Epidemiological interpretation of studies examining the effect of antibiotic usage on resistance

Bacterial resistance to antibiotics is a growing clinical problem and public health threat. Antibiotic use is a known risk factor for the emergence of antibiotic resistance, but demonstrating the causal link between antibiotic use and resistance is challenging. This review describes different study designs for assessing the association between antibiotic use and resistance and discusses strengths and limitations of each. Approaches to measuring antibiotic use and antibiotic resistance are presented. Important methodological issues such as confounding, establishing temporality, and control group selection are examined.

Methicillin-resistant Staphylococcus aureus (MRSA) is increasing in Norway: a time series analysis of reported MRSA and methicillin-sensitive S. aureus cases, 1997-2010

BACKGROUND

Accurate estimates of the incidence and prevalence of methicillin-resistant Staphylococcus aureus (MRSA) infections are needed to inform public health policies. In Norway, where both MRSA infection and carriage are notifiable conditions, the reported incidence of MRSA is slowly increasing. However, the proportion of MRSA in relation to all S. aureus isolates is unknown, making it difficult to determine if the rising incidence is real or an artifact of an increasing number of tests performed.

AIM

To characterize recent trends in MRSA infections and obtain a more complete understanding of the MRSA level in Norway.

METHODS

All reported cases of MRSA and methicillin-sensitive S. aureus (MSSA) from Oslo County (1997-2010) and Health Region East (2008-2008), representing approximately 11% and 36% of the Norwegian population, respectively, were analyzed using a stochastic time series analysis to characterize trends.

RESULTS

In Oslo County, the proportion of methicillin-resistant cases increased from 0.73% to 3.78% during the study period and was well modeled by an exponential growth with a doubling constant of 5.7 years (95% CI 4.5-7.4 years). In Health Region East, the proportion of MRSA cases increased from 0.4% to 2.1% from 2002 to 2008, with a best-fitting linear increase of 0.26% (95% CI 0.21-0.30%) per year. In both cases, the choice of a linear or exponential model for the time trend produced only marginally different model fits. We found no significant changes due to revised national MRSA guidelines published in June 2009. Significant variations in the increasing time trend were observed in the five hospitals within the region. The yearly reported incidence of MSSA was relatively stable in both study areas although we found seasonal patterns with peaks in August.

CONCLUSION

The level of MRSA is increasing in Norway, and the proportion of methicillin resistance in all S. aureus isolates are higher than the reported proportion of MRSA in invasive infections.

Can the antibiogram be used to assess microbiologic outcomes after antimicrobial stewardship interventions? A critical review of the literature

Hospitals are implementing antimicrobial stewardship programs (ASPs) in response to national guidelines to improve the use and to extend the utility of antiinfective drugs. An often implied purpose of ASPs is to curb or reverse the emergence of resistant bacteria. Because antibiotic use causes antibiotic resistance, there is a natural tendency to link local measures of antibiotic use to local measures of bacterial resistance, and the hospital antibiogram is a readily available measure of resistance. We performed a literature review to identify published reports that used hospitalwide and unit-specific antibiograms to assess the relationship of ASP interventions to changes in resistance. Eight studies were identified and reviewed. The relationship between hospital antibiotic use and resistance is complex, and the existing literature has several limitations. Furthermore, the antibiogram itself is neither designed nor well suited to reflect changes in hospital antimicrobial drug use. The literature on the effectiveness of ASPs in reducing resistance continues to emerge, but at this time the antibiogram bears an inconsistent relationship with changes in hospital antibiotic use and cannot be recommended to reliably evaluate an ASP intervention. Interrupted time series analysis is a superior strategy to assess the effect of an ASP intervention on bacterial resistance, but it is not widely used because of its complexity and greater data requirements. Nevertheless, before ASP efforts can be convincingly demonstrated to have a favorable impact on resistance, a more sophisticated approach that links drug use to resistance should become a priority, at least for hospitals that have sufficient resources.

Improving antibiotic stewardship by involving nurses

Antimicrobial stewardship programs are important preventative strategies to reduce hospital-acquired infection, typically involving medical and pharmacy staff. Because nurses are pivotal in administering medication prescribed by medical staff and filled by pharmacy staff, we assessed nursing attitudes and antimicrobial stewardship knowledge before and after an education intervention that focused on nursing involvement in antimicrobial management. This study supports involving nurses as a means of improving antibiotic stewardship.

Time series analysis as a tool to predict the impact of antimicrobial restriction in antibiotic stewardship programs using the example of multidrug-resistant Pseudomonas aeruginosa

The association between antimicrobial consumption and resistance in nonfermentative Gram-negative bacteria is well-known. Antimicrobial restriction, implemented in clinical routines by antibiotic stewardship programs (ASPs), is considered a means to reduce resistance rates. Whether and how antimicrobial restriction can accomplish this goal is still unknown though. This leads to an element of uncertainty when designing strategies for ASPs. From January 2002 until December 2011, an observational study was performed at the University Hospital Tübingen, Tübingen, Germany, to investigate the association between antimicrobial use and resistance rates in Pseudomonas aeruginosa. Transfer function models were used to determine such associations and to simulate antimicrobial restriction strategies. Various positive associations between antimicrobial consumption and resistance were observed in our setting. Surprisingly, impact estimations of different antimicrobial restriction strategies revealed relatively low intervention expenses to effectively attenuate the observed increase in resistance. For example, a simulated intervention of an annual 4% reduction in the use of meropenem over 3 years from 2009 until 2011 yielded a 62.5% attenuation (95% confidence interval, 15% to 110%) in the rising trend of multidrug-resistant Pseudomonas aeruginosa (three- and four-class-resistant P. aeruginosa [34MRGN-PA]). Time series analysis models derived from past data may be a tool to predict the outcome of antimicrobial restriction strategies, and could be used to design ASPs.

Time series analysis of human and bovine brucellosis in South Korea from 2005 to 2010

Brucellosis is considered to be one of the most important zoonotic diseases in the world, affecting underdeveloped and developing countries. The primary purpose of brucellosis control is to prevent the spread of disease from animals (typically ruminants) to humans. The main objective of this study was to retrospectively develop an appropriate time series model for cattle-to-human transmission in South Korea using data from independent national surveillance systems. Monthly case counts for cattle and people as well as national population data were available for 2005-2010. The temporal relationship was evaluated using an autoregressive integrated moving average with exogenous input (ARIMAX) model [notated as ARIMA(p, d, q)-AR(p)] and a negative binomial regression (NBR) model. Human incidence rate was highly correlated to cattle incidence rate in the same month and the previous month (both r=0.82). In the final models, ARIMA (0, 1, 1)-AR (0, 1) was determined as the best fit with 191.5% error in the validation phase, whereas the best NBR model including lags (0, 1 months) for the cattle incidence rate yielded a 131.9% error in the validation phase. Error (MAPE) rates were high due to small absolute human case numbers (typically less than 10 per month in the validation phase). The NBR model however was able to demonstrate a marked reduction in human case immediately following a hypothetical marked reduction in cattle cases, and may be better for public health decision making.

Spatial exploration of Streptococcus pneumoniae clonal clustering in São Paulo, Brazil

OBJECTIVES

To examine the spatial distribution of Streptococcus pneumoniae and its clonal patterns collected between 2002 and 2006 in São Paulo, Brazil.

METHODS

As part of an observational study in São Paulo city, Brazil, S. pneumoniae isolates routinely cultured from blood, respiratory specimens, or cerebrospinal and other profound fluids were selected. Additionally, only isolates with either penicillin (PEN) intermediate (I) or resistant (R) status on routine antibiogram were included, in order to obtain a higher probability of clonal isolates. A single I/R S. pneumoniae isolate per patient was included and submitted to genotypic determination by pulsed field gel electrophoresis (PFGE). Minimum inhibitory concentrations (MICs) were determined for the isolates by Etest® to PEN and other antimicrobials. Each isolate was geocoded in a digital map. The Kernel function and ratio methods between total isolates vs. clones were used in order to explore possible cluster formations.

RESULTS

Seventy-eight (78) S. pneumoniae community isolates from two major outpatient centers in São Paulo, Brazil, were selected from the databank according to their penicillin susceptibility profile, i.e. R or I to penicillin assessed by oxacillin disc diffusion. Of these, 69 were submitted to PFGE, 65 to MIC determination, and 48 to spatial analytical procedures. Preliminary spatial analysis method showed two possible cluster formation located in southwest and southeast regions of the city.

CONCLUSION

Further analyses are required for precisely determining the existence of S. pneumoniae clusters and their related risk factors. Apparently there is a specific transmission pattern of S. pneumoniae clones within certain regions and populations. GIS and spatial methods can be applied to better understand epidemiological patterns and to identify target areas for public health interventions.

An evaluation of the impact of antibiotic stewardship on reducing the use of high-risk antibiotics and its effect on the incidence of Clostridium difficile infection in hospital settings

OBJECTIVES

To evaluate the impact of a high-risk antibiotic stewardship programme on reducing antibiotic use and on hospital Clostridium difficile infection (CDI) incidence rates. A secondary objective was to present the possible utility of time-series analysis as an antibiotic risk classification tool.

METHODS

This was an interventional, retrospective, ecological investigation in a medium-sized hospital over 6.5 years (January 2004 to June 2010). The intervention was the restriction of high-risk antibiotics (second-generation cephalosporins, third-generation cephalosporins, fluoroquinolones and clindamycin). Amoxicillin/clavulanic acid and macrolides were classified as medium-risk antibiotics based on time-series analysis findings and their use was monitored. The intervention was evaluated by segmented regression analysis of interrupted time series.

RESULTS

The intervention was associated with a significant change in level of use of high-risk antibiotics (coefficient -17.3, P < 0.0001) and with a borderline significant trend change in their use being reduced by 0.156 defined daily doses/100 bed-days per month (P = 0.0597). The reduction in the use of high-risk antibiotics was associated with a significant change in the incidence trend of CDI (P = 0.0081), i.e. the CDI incidence rate decreased by 0.0047/100 bed-days per month. Analysis showed that variations in the incidence of CDI were affected by the age-adjusted comorbidity index with a lag of 1 month (coefficient 0.137051, P = 0.0182). Significant decreases in slope (coefficient -0.414, P = 0.0309) post-intervention were also observed for the monitored medium-risk antibiotics.

CONCLUSIONS

The restriction of the high-risk antibiotics contributed to both a reduction in their use and a reduction in the incidence of CDI in the study site hospital. Time-series analysis can be utilized as a risk classification tool with utility in antibiotic stewardship design and quality improvement programmes.

Seasonality and temporal correlation between community antibiotic use and resistance in the United States

BACKGROUND

Therapeutic antibiotic use in humans is a significant driver of antibiotic resistance. The seasonal effect of antibiotic use on antibiotic resistance has been poorly quantified because of lack of large-scale, spatially disaggregated time-series data on antibiotic use and resistance.

METHODS

We used time-series analysis (Box-Jenkins) on US antibiotic usage from IMS Health and on antibiotic resistance from The Surveillance Network from 1999-2007 to estimate the effect of aminopenicillin, fluoroquinolone, trimethoprim/sulfamethoxazole, and tetracycline usage on resistance of Escherichia coli to drugs within these classes. We also quantified the effect of fluoroquinolone and macrolide/lincosamide usage on resistance of methicillin-resistant Staphylococcus aureus (MRSA) to ciprofloxacin and clindamycin (which has a similar mode of action to macrolides), respectively.

RESULTS

Prevalence of resistant Escherichia coli was significantly correlated with lagged (by 1 month) antibiotic prescriptions for aminopenicillins (0.22, P = .03) and fluoroquinolones (0.24, P = .02), which are highly prescribed, but was uncorrelated to antibiotic classes with lower prescription levels. Fluoroquinolone prescriptions were also significantly correlated with a 1-month lag with the prevalence of ciprofloxacin-resistant MRSA (0.23, P = .03).

CONCLUSIONS

Large-scale usage of antibiotics can generate seasonal patterns of resistance that fluctuate on a short time scale with changes in antibiotic retail sales, suggesting that use of antibiotics in the winter could have a significant effect on resistance. In addition, the strong correlation between community use of antibiotics and resistance isolated in the hospital indicates that restrictions imposed at the hospital level are unlikely to be effective unless coordinated with campaigns to reduce unnecessary antibiotic use at the community level.

Seasonal variations in Clostridium difficile infections are associated with influenza and respiratory syncytial virus activity independently of antibiotic prescriptions: a time series analysis in Quebec, Canada

Seasonal variations in Clostridium difficile-associated diarrhea (CDAD), with a higher incidence occurring during winter months, have been reported. Although winter epidemics of respiratory viruses may be temporally associated with an increase in CDAD morbidity, we hypothesized that this association is mainly due to increased antibiotic use for respiratory infections. The objective of this study was to evaluate the effect of the two most frequent respiratory viruses (influenza virus and respiratory syncytial virus [RSV]) and antibiotics prescribed for respiratory infections (fluoroquinolones and macrolides) on the CDAD incidence in hospitals in the province of Québec, Canada. A multivariable Box-Jenkins transfer function model was built to relate monthly CDAD incidence to the monthly percentage of positive tests for influenza virus and RSV and monthly fluoroquinolone and macrolide prescriptions over a 4-year period (January 2005 to December 2008). Analysis showed that temporal variations in CDAD incidence followed temporal variations for influenza virus (P = 0.043), RSV (P = 0.004), and macrolide prescription (P = 0.05) time series with an average delay of 1 month and fluoroquinolone prescription time series with an average delay of 2 months (P = 0.01). We conclude that influenza virus and RSV circulation is independently associated with CDAD incidence after controlling for fluoroquinolone and macrolide use. This association was observed at an aggregated level and may be indicative of other phenomena occurring during wintertime.

Scoring system development and validation for initial treatment failure in suppurative kidney infections

BACKGROUND

Suppurative kidney infections (SKIs) have potentially lethal implications and a high incidence of treatment-related morbidity and death. Until this point, there has been no study that has derived a prognostic model for adverse early outcomes in SKI. Therefore, our aim was to derive and validate a simple scoring system of early treatment failure in SKI.

METHODS

Logistic regression and bootstrap methods were used to create an integer score for estimating the risk of early treatment failure using patient characteristics, severity of disease, bacterial etiology, type of pathology, initial antibiotic therapy, and early urologic procedures.

RESULTS

This study included 92 adult patients with 104 SKIs. Early treatment failure was observed in 57 patients (54.8%). The length of the hospital stay and the treatment complications were significantly longer and more common, respectively, in patients with early treatment failure. The factors associated most strongly with early treatment outcome were whether there had been an early complete urologic procedure, the adequacy of early antibiotic therapy, and the presence or absence of sepsis syndrome. The total possible score ranged from 0 to 22 points, with a cut-off value of 5 points. A score of ≤ 5 points identified early success correctly in 85.3% of patients, whereas a score > 5 points correctly identified early failure in 93.2%. The scoring system retained its predictive ability on the validation set.

CONCLUSION

A scoring system was created to predict early treatment failure for a given patient with SKI. Although the system has good performance characteristics and provides a possible intervention measure, further studies should be performed before widespread implementation.

A spatial approach for the epidemiology of antibiotic use and resistance in community-based studies: the emergence of urban clusters of Escherichia coli quinolone resistance in Sao Paulo, Brasil

BACKGROUND

Population antimicrobial use may influence resistance emergence. Resistance is an ecological phenomenon due to potential transmissibility. We investigated spatial and temporal patterns of ciprofloxacin (CIP) population consumption related to E. coli resistance emergence and dissemination in a major Brazilian city. A total of 4,372 urinary tract infection E. coli cases, with 723 CIP resistant, were identified in 2002 from two outpatient centres. Cases were address geocoded in a digital map. Raw CIP consumption data was transformed into usage density in DDDs by CIP selling points influence zones determination. A stochastic model coupled with a Geographical Information System was applied for relating resistance and usage density and for detecting city areas of high/low resistance risk.

RESULTS

E. coli CIP resistant cluster emergence was detected and significantly related to usage density at a level of 5 to 9 CIP DDDs. There were clustered hot-spots and a significant global spatial variation in the residual resistance risk after allowing for usage density.

CONCLUSIONS

There were clustered hot-spots and a significant global spatial variation in the residual resistance risk after allowing for usage density. The usage density of 5-9 CIP DDDs per 1,000 inhabitants within the same influence zone was the resistance triggering level. This level led to E. coli resistance clustering, proving that individual resistance emergence and dissemination was affected by antimicrobial population consumption.

Modelling the impact of antibiotic use on antibiotic-resistant Escherichia coli using population-based data from a large hospital and its surrounding community

OBJECTIVES

To determine the temporal relationship between antibiotic use and incidence of antibiotic-resistant Escherichia coli in both the inpatient and outpatient setting of a large urban area.

METHODS

A retrospective observational time-series analysis was performed to evaluate the incidence of non-duplicate clinical isolates of E. coli resistant to ciprofloxacin, trimethoprim/sulfamethoxazole and cefepime from January 2000 through December 2007, combined with a transfer function model of aggregated data on antibiotic use in both settings obtained from the hospital's pharmacy and outpatient billing offices.

RESULTS

Ciprofloxacin resistance increased from 6.0% (2000) to 15.4% (2007; P<0.0001) and cefepime resistance from 0.9% (2002) to 3.2% (2007; P=0.01). Trimethoprim/sulfamethoxazole resistance remained stable (23.7%-25.8%). Total antibiotic use increased in both settings, while fluoroquinolone use increased significantly only among outpatients. A temporal effect between fluoroquinolone resistance in community E. coli isolates and outpatient use of ciprofloxacin (immediate effect and time lag 1 month) and moxifloxacin (time lag 4 months) was observed, explaining 51% of the variance over time. The incidence of cefepime resistance in E. coli was correlated with ciprofloxacin use in the inpatient (lag 1 month) and outpatient (lag 4 months) settings and with the use of ceftriaxone (lag 0 month), piperacillin/tazobactam (3 months) and cefepime (3 months) in the hospital (R2=51%).

CONCLUSIONS

These results support efforts to reduce prescribing of fluoroquinolones for control of resistant E. coli including extended-spectrum β-lactamase producers and show the added value of time-series analysis to better understand the interaction between community and hospital antibiotic prescribing and its spill-over effect on antibiotic resistance.

Identification of targets for quality improvement in antimicrobial prescribing: the web-based ESAC Point Prevalence Survey 2009

OBJECTIVES

Since electronic prescribing is limited to few hospitals, point prevalence surveys, such as the standardized European Surveillance of Antimicrobial Consumption point prevalence survey (ESAC PPS), are an alternative tool for monitoring prescribing and helping to identify performance indicators and prescribing trends. The main objective of this study was to identify and assess targets for quality improvement.

METHODS

Each hospital had to carry out the survey within 2 weeks. Each department had to be surveyed in 1 day. Data collected, for all inpatients, included age and gender. For patients on systemic antimicrobial treatment, the antimicrobial/s, infection/prophylaxis site, reason in medical notes and guideline compliance were also collected. A central database using a web-based tool (WebPPS) developed in-house was used for data entry.

RESULTS

Combination of two or more antimicrobials accounted for 30% of use. Surgical prophylaxis was prolonged (>1 day) in 53% of cases. 'Intensive care' had higher proportions of treated patients (53% versus 29%), combination therapy (49% versus 31%), hospital-acquired infections (49% versus 31%) and parenteral administration (91% versus 61%). 'Reason in notes' was documented in 76%, and 'guideline compliance' occurred in 62% of patients.

CONCLUSIONS

The ESAC PPS provided useful information on the quality of prescribing, which identified a number of targets for quality improvement. These could apply to specific departments or whole hospitals. Intensive care, which has different characteristics, should not be compared with general wards with respect to combination therapy, hospital-acquired infections or parenteral proportion. The study confirmed that the ESAC PPS methodology can be used on a large number of hospitals at regional, national, continental or global level.

Influence of fluoroquinolone consumption in inpatients and outpatients on ciprofloxacin-resistant Escherichia coli in a university hospital

BACKGROUND

The increase in fluoroquinolone-resistant Escherichia coli has raised the issue of treatment failure in common infections. Few studies have investigated the possible relationship between outpatient fluoroquinolone consumption and resistance in hospital.

OBJECTIVE

To investigate the relationship between inpatient and outpatient fluoroquinolone use and ciprofloxacin-resistant E. coli in a teaching hospital.

METHODS

An ecological study was conducted in Toulouse University Hospital and its surrounding area, the Midi-Pyrénées region (south-western France), in 2004-07. Dynamic regression models were built to study how the hospital resistance rate was linearly related to current and past values of fluoroquinolone consumption. Resistance forecasts for 2008 were then calculated and compared with actual rates for the first 5 months of the year.

RESULTS

Mean resistance rate was 13.7% and mean fluoroquinolone use was 89.9 defined daily doses (DDDs)/1000 inpatient days in hospital and 2.6 DDDs/1000 inhabitants/day in the region. Taking into account past values of fluoroquinolone consumption in hospital and in outpatients, only levofloxacin use in the community remained significantly associated with resistance in hospital, with a lag of 12 months. This model explained 50% of the resistance variability.

CONCLUSIONS

This ecological analysis, conducted on a teaching hospital scale, suggests that ciprofloxacin resistance in E. coli in hospital is linked to consumption of fluoroquinolones within the hospital and its surrounding community. Among all fluoroquinolones, levofloxacin use was found to be the most important factor. Consumption in outpatients appears to be a relevant determinant to consider in designing interventions to reduce resistance in hospitals.

Antibiotic prescribing in hospitals: a social and behavioural scientific approach

Antibiotics have dramatically changed the prognoses of patients with severe infectious diseases over the past 50 years. However, the emergence and dissemination of resistant organisms has endangered the effectiveness of antibiotics. One possible approach to the resistance problem is the appropriate use of antibiotic drugs for preventing and treating infections. This Review describes how the volume and appropriateness of antibiotic use in hospitals vary between countries, hospitals, and physicians. At each specific level-cultural, contextual, and behavioural-we discuss the determinants that influence hospital antibiotic use and the possible improvement strategies to make it more appropriate. Changing hospital antibiotic use is a challenge of formidable complexity. On each level, many determinants play a part, so that the measures or strategies undertaken to improve antibiotic use need to be equally diverse. Although various strategies for improving antibiotic use are available, a programme with activities at all three levels is needed for hospitals. Evaluating these programme activities in a way that provides external validity of the conclusions is crucial.

Temporal effects of antibiotic use and Clostridium difficile infections

OBJECTIVES

We tested a previously published model for the analysis of the temporal relationship between antibiotic use and the incidence of Clostridium difficile infection in a hospital with stable incidence of infection at >1 case per 1000 admissions per month.

METHODS

The study period was from April 2004 to June 2008 and used data from Infection Control and Hospital Pharmacy. We first described the monthly variation in C. difficile infection and then constructed a multivariate transfer function model that included lag time (cases of C. difficile infection in previous months and delays between changes in antibiotic use and changes in C. difficile infection).

RESULTS

The average incidence of C. difficile infection was 1.5 cases per 1000 patients per month with no significant increase over 3 years. The number of cases of C. difficile infection in 1 month was dependent on the average number of cases of C. difficile infection in the previous 2 months. The models with data from the whole hospital showed a statistically significant relationship between the number of both hospital-acquired C. difficile infections and total C. difficile infections and consumption of piperacillin/tazobactam, ciprofloxacin and cefuroxime. The association between C. difficile infection and consumption of co-amoxiclav was only significant for hospital-acquired C. difficile infection. The model for hospital-acquired C. difficile infections explained 61% of the variance in C. difficile infections.

CONCLUSIONS

These results provide support for antibiotic policies that minimize the use of broad-spectrum penicillins (co-amoxiclav and piperacillin/tazobactam), cephalosporins and fluoroquinolones.

Two time-series analyses of the impact of antibiotic consumption and alcohol-based hand disinfection on the incidences of nosocomial methicillin-resistant Staphylococcus aureus infection and Clostridium difficile infection

OBJECTIVE

To determine the impact of antibiotic consumption and alcohol-based hand disinfection on the incidences of nosocomial methicillin-resistant Staphylococcus aureus (MRSA) infection and Clostridium difficile infection (CDI).

METHODS

Two multivariate time-series analyses were performed that used as dependent variables the monthly incidences of nosocomial MRSA infection and CDI at the Freiburg University Medical Center during the period January 2003 through October 2007. The volume of alcohol-based hand rub solution used per month was quantified in liters per 1,000 patient-days. Antibiotic consumption was calculated in terms of the number of defined daily doses per 1,000 patient-days per month.

RESULTS

The use of alcohol-based hand rub was found to have a significant impact on the incidence of nosocomial MRSA infection (P< .001). The multivariate analysis (R2=0.66) showed that a higher volume of use of alcohol-based hand rub was associated with a lower incidence of nosocomial MRSA infection. Conversely, a higher level of consumption of selected antimicrobial agents was associated with a higher incidence of nosocomial MRSA infection. This analysis showed this relationship was the same for the use of second-generation cephalosporins (P= .023), third-generation cephalosporins (P= .05), fluoroquinolones (P= .01), and lincosamides (P= .05). The multivariate analysis (R2=0.55) showed that a higher level of consumption of third-generation cephalosporins (P= .008), fluoroquinolones (P= .084), and/or macrolides (P= .007) was associated with a higher incidence of CDI. A correlation with use of alcohol-based hand rub was not detected.

CONCLUSION

In 2 multivariate time-series analyses, we were able to show the impact of hand hygiene and antibiotic use on the incidence of nosocomial MRSA infection, but we found no association between hand hygiene and incidence of CDI.

The dynamic relationship between antibiotic use and the incidence of vancomycin-resistant Enterococcus: time-series modelling of 7-year surveillance data in a tertiary-care hospital

The role of antibiotics in the epidemiology of vancomycin-resistant Enterococcus (VRE) has been studied extensively, but controversies remain as to which, and to what extent, antibiotics facilitate the emergence and dissemination of VRE in hospitals. Aggregate data on the use of several antibiotic classes in terms of defined daily doses (DDD) per 100 patient-days (PD), and VRE incidence rates in terms of clinical isolates per 1000 PD, were evaluated during a 7-year period at a tertiary-care hospital. Time-series analysis (autoregressive integrated moving average (ARIMA) and transfer function models) was used to quantify the temporal effect of antibiotic use on VRE incidence and estimate effect-delays. The incidence rate of VRE observed in a specific bimester was found to be a function of its value during the preceding bimester and of prior changes in the volume of use of four antibiotic classes. In particular, an increase of one DDD/100 PD in the use of glycopeptides, fluoroquinolones, extended-spectrum cephalosporins and beta-lactam-beta-lactamase inhibitor combinations resulted, independently, in average changes of +0.024, +0.015, + 0.020 and -0.010 isolates per 1000 PD in the incidence of VRE, with average delays of 2, 4, 2 and 6 months, respectively, which explained 56% of the observed variation in VRE rates over time. Efforts to reduce VRE cross-transmission should be supplemented by targeted antibiotic control policies. The use of glycopeptides, broad-spectrum cephalosporins and fluoroquinolones in high amounts should be the targets of such policies. Penicillin-beta-lactamase inhibitor combinations might be suitable substitutes for extended-spectrum cephalosporins.

Differential correlation between rates of antimicrobial drug consumption and prevalence of antimicrobial resistance in a tertiary care hospital in Greece

OBJECTIVE

To investigate whether there is a correlation between the rates of antimicrobial drug consumption in hospital departments and the prevalence of antimicrobial resistance among clinically important bacteria recovered in the hospital.

DESIGN

Retrospective study.

SETTING

Tertiary care hospital in Greece.

METHODS

Data on antimicrobial consumption (from January 2001 through December 2004) were expressed as defined daily doses per 100 bed-days. The prevalence of antimicrobial resistance among isolates of Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Acinetobacter baumannii, and Enterococcus faecium recovered during the same time period were calculated by the microbiology department. We then performed the following analyses: (1) a comparison of the consumption rates for different antimicrobial groups in individual hospital departments, (2) a comparison of the prevalence of resistance to different antimicrobials, and (3) a correlation analysis of antimicrobial consumption rates and the prevalence of antimicrobial resistance.

RESULTS

The rates of antimicrobial consumption and the prevalence of resistance varied substantially among the hospital's departments. The annual rate of consumption for carbapenems correlated with the rate of consumption for glycopeptides and third-generation cephalosporins (P < .05). Among P. aeruginosa isolates, the prevalence of imipenem resistance correlated with the prevalence of resistance to amikacin, ciprofloxacin, and ceftazidime (P < .05). The rate of carbapenem consumption correlated with the prevalence of imipenem resistance among P. aeruginosa and A. baumannii isolates (P < .05). The rate of aminoglycoside consumption correlated with the prevalence of amikacin resistance among P. aeruginosa, K. pneumoniae, and E. coli isolates (P < .05). However, the rate of consumption for fluoroquinolones and glycopeptides had no correlation with the prevalence of ciprofloxacin resistance among gram-negative bacteria or vancomycin resistance among E. faecium isolates.

CONCLUSIONS

These data are suggestive of a differential relationship between antimicrobial consumption and the prevalence of antimicrobial resistance among various species and for various antimicrobial agents. These findings may help to optimize antimicrobial prescription policies in the hospital, especially in departments that have both high rates of antimicrobial consumption and a high prevalence of antimicrobial resistance.

Association between antibiotic use and changes in susceptibility patterns of Pseudomonas aeruginosa in an intensive care burn unit: a 5-year study, 2000-2004

This study aimed to evaluate the relationship between antimicrobial resistance in Pseudomonas aeruginosa and annual antibiotic use in a burn unit. From 1 January 2000 to 31 December 2004, 203 non-repetitive strains of Ps. aeruginosa were recovered from various clinical specimens. Antimicrobial susceptibility testing was performed using the disc diffusion method, and susceptibility data were interpreted according to break points recommended by the French Society of Microbiology. The antibiotic consumption for imipenem, ceftazidime, cefotaxime, piperacillin-tazobactam, ofloxacin, ciprofloxacin, gentamicin and amikacin was calculated with antimicrobial density. The relationship between antibiotic use and the resistance of Ps. aeruginosa was analysed. The consumption of ceftazidime and amikacin showed no association with resistance. A statistically significant relationship was observed between increasing use of ciprofloxacin and the incidence of resistant Ps. aeruginosa to this antibiotic (rs=0.89, p=0.05), and a significant correlation between ciprofloxacin consumption and resistance to imipenem was noted (rs=0.89, p=0.043). Restricted use of ciprofloxacin during 2003 and 2004 was followed by a significant decrease of resistance in Ps. aeruginosa. Our report illustrates the major role of ciprofloxacin in the emergence of resistant Ps. aeruginosa.

Temporal effects of antibiotic use and hand rub consumption on the incidence of MRSA and Clostridium difficile

OBJECTIVES

The aim of this study was to determine the temporal relation between the use of antibiotics and alcohol-based hand rubs (ABHRs) and the incidence of methicillin-resistant Staphylococcus aureus (MRSA) and Clostridium difficile.

METHODS

An interventional time-series analysis was performed to evaluate the impact of two promotion campaigns on the consumption of ABHRs and to assess their effect on the incidence of non-duplicate clinical isolates of MRSA and C. difficile from February 2000 through September 2006. This analysis was combined with a transfer function model of aggregated data on antibiotic use.

RESULTS

Consumption of ABHRs correlated with MRSA, but not with C. difficile. The final model demonstrated the immediate effect of the second hand hygiene promotion campaign and an additional temporal effect of fluoroquinolone (time lag, 1 month; i.e. antibiotic effect delayed for 1 month), macrolide (lag 1 and 4 months), broad-spectrum cephalosporins (lag 3, 4 and 5 months) and piperacillin/tazobactam (lag 3 months) use. The final model explained 57% of the MRSA variance over time. In contrast, the model for C. difficile showed only an effect for broad-spectrum cephalosporins (lag 1 month).

CONCLUSIONS

We observed an aggregate-level relation between the monthly MRSA incidence and the use of different antibiotic classes and increased consumption of ABHR after a successful hand hygiene campaign, while no association with ABHR use was detected for C. difficile.

Modelling the impact of antibiotic use and infection control practices on the incidence of hospital-acquired methicillin-resistant Staphylococcus aureus: a time-series analysis

OBJECTIVES

Methicillin-resistant Staphylococcus aureus (MRSA) is a major nosocomial pathogen worldwide. A wide range of factors have been suggested to influence the spread of MRSA. The objective of this study was to evaluate the effect of antimicrobial drug use and infection control practices on nosocomial MRSA incidence in a 426-bed general teaching hospital in Northern Ireland.

METHODS

The present research involved the retrospective collection of monthly data on the usage of antibiotics and on infection control practices within the hospital over a 5 year period (January 2000-December 2004). A multivariate ARIMA (time-series analysis) model was built to relate MRSA incidence with antibiotic use and infection control practices.

RESULTS

Analysis of the 5 year data set showed that temporal variations in MRSA incidence followed temporal variations in the use of fluoroquinolones, third-generation cephalosporins, macrolides and amoxicillin/clavulanic acid (coefficients = 0.005, 0.03, 0.002 and 0.003, respectively, with various time lags). Temporal relationships were also observed between MRSA incidence and infection control practices, i.e. the number of patients actively screened for MRSA (coefficient = -0.007), the use of alcohol-impregnated wipes (coefficient = -0.0003) and the bulk orders of alcohol-based handrub (coefficients = -0.04 and -0.08), with increased infection control activity being associated with decreased MRSA incidence, and between MRSA incidence and the number of new patients admitted with MRSA (coefficient = 0.22). The model explained 78.4% of the variance in the monthly incidence of MRSA.

CONCLUSIONS

The results of this study confirm the value of infection control policies as well as suggest the usefulness of restricting the use of certain antimicrobial classes to control MRSA.