Antimicrobial use and antimicrobial resistance: a population perspective

Pre-dispensing of antivirals to high-risk individuals in an influenza pandemic

We consider the net benefits of pre-dispensing antivirals to high-risk individuals during an influenza pandemic, where the measure of the benefit is the number of severe outcomes (such as deaths or hospitalizations) prevented by antivirals in the whole population. One potential benefit of pre-dispensing is that individuals to whom antivirals have been pre-dispensed may be able to initiate treatment earlier than if they had to wait to obtain and fill a prescription, reducing their risk of progression to severe disease. If this benefit exceeds the side effects of misuse for the category of individuals to whom antivirals were pre-dispensed, and if antiviral supply exceeds overall population demand (which appears relevant for several countries including US in the 2009 H1N1 pandemic), pre-dispensing a quantity of antivirals not exceeding the difference between supply and demand is always beneficial. In this study, we consider the net benefits of pre-dispensing antivirals under various scenarios, including demand exceeding supply, and derive mathematical conditions under which antiviral pre-dispensing is advantageous on balance. For individuals whose relative risk of severe outcome is high enough, such as immunosuppressed individuals (particularly children) and possibly individuals with neurological disorders, pre-dispensing is always beneficial at a given level of antiviral stockpile with modest assumptions on the relative benefit of early treatment by a pre-dispensed course, regardless of the overall population demand for antivirals during the course of an epidemic. Making additional assumptions on either the overall population demand for antivirals (which appear relevant for the 2009 H1N1 pandemic) or on the relative benefit of pre-dispensing would make pre-dispensing net beneficial with inclusion of a larger number of persons such as pregnant women and morbidly obese adults.

Reduced antibiotic prescribing for acute respiratory infections in adults and children

BACKGROUND

Recent public health efforts, including in the UK and US, have targeted decreasing unnecessary antibiotic use. In the US, prescribing for acute non-specific respiratory infections (ARIs) has decreased, but broad-spectrum antibacterial prescribing has soared.

AIM

To assess recent trends in antibacterial prescribing for ARIs in the UK.

DESIGN OF STUDY

Retrospective cohort.

SETTING

The Health Improvement Network database.

METHOD

Outpatient ARI visits from 1 January 1990 to 31 December 2004 were selected. Outcomes were antibacterial and broad-spectrum antibacterial prescriptions per thousand person-years, and the probability of receiving an antibacterial and broad-spectrum prescription conditional on an ARI visit.

RESULTS

From 1990 to 2004, antibacterial prescribing rates for ARIs decreased from 55.0 to 30.3 prescriptions/1000 person-years for adults and from 124.8 to 46.3 prescriptions/1000 person-years for children (P=0.001). The probability of receiving an antibacterial prescription after an ARI visit decreased from 70.8% to 59.5% for adults and from 46.1% to 30.8% for children (P=0.003 and 0.007, respectively). Antibacterial prescribing declined faster for younger than for older adults. Broad-spectrum antibacterial prescribing rates decreased from 3.8 to 2.9 prescriptions/1000 person-years for adults and from 5.2 to 2.2 prescriptions/1000 person years for children (P=0.005 and 0.003, respectively). The probability of broad-spectrum prescribing did not demonstrate a significant linear trend for adults (P=0.16), and decreased for children (P=0.01).

CONCLUSION

UK antibacterial prescribing for ARIs has declined, similar to US trends, but there was no concomitant increase in low broad-spectrum prescribing. The success of UK strategies for limiting antimicrobial use has implications for programmes in other countries.

Trends in antimicrobial prescribing rates for Alaska Native and American Indian persons <18 years of age residing in the Anchorage region

OBJECTIVES

In the U.S., the total number of antimicrobials prescribed in ambulatory care declined between 1989 and 2000; however, antimicrobial resistance increased among many pathogens. We evaluated antimicrobial prescribing patterns from 1992 to 2004 in Alaska Native/American Indian (AI/AN) persons

STUDY DESIGN

Retrospective study based on medical records.

METHODS

Medical records were used to obtain data on oral antibiotics prescribed for ambulatory and emergency-room visits. Antimicrobial prescribing rates were calculated per population and per ambulatory-clinic visit.

RESULTS

The total number of antimicrobial courses prescribed increased 94% from 4,929 (1992) to 9,561 (2004). However, the total number of ambulatory-clinic visits also increased (79%) from 49,008 (1992) to 87,486 (2004), while the population of AI/AN persons <18 in Anchorage region rose 14%. The population-based rate of antimicrobial prescriptions (per 1,000 persons) rose from 309 (1992) to 524 (2004 (p<0.001). The visit-based annual rate (per 1,000 visits) remained stable from 101 (1992) to 109 (2004) (=0.651). Overall, visit-based prescriptions rates in AI/AN persons were lower than previously reported among children in the U.S. (range 250-340). Penicillins comprised >50% of antimicrobials presribed from 1992 to 2004. Visit-based prescribing rates from 1992 to 2004 changed: penicillin, +27% (p=0.210): cephalosporins, +33% (p=0.23); trimethoprim-sulfamethexazole, -48% (p<0.001).

CONCLUSIONS

Visit -based antimicrobial prescribing rates in the Anchorage region for AI/AN children receiving care in the AI/AN health system have been stable over a 13-year period. Although a trend in decreased antibiotic prescribing has been seen in the general U.S. population, visit-based prescribing rates in the Anchorage region for AI/AN children have remained below those in previous studies in the U.S.

The antigenome: from protein subunit vaccines to antibody treatments of bacterial infections?

New strategies are needed to master infectious diseases. The so-called "passive vaccination", i.e., prevention and treatment with specific antibodies, has a proven record and potential in the management of infections and entered the medical arena more than 100 years ago. Progress in the identification of specific antigens has become the hallmark in the development of novel subunit vaccines that often contain only a single immunogen, frequently proteins, derived from the microbe in order to induce protective immunity. On the other hand, the monoclonal antibody technology has enabled biotechnology to produce antibody species in unlimited quantities and at reasonable costs that are more or less identical to their human counterparts and bind with high affinity to only one specific site of a given antigen. Although, this technology has provided a robust platform for launching novel and successful treatments against a variety of devastating diseases, it is up till now only exceptionally employed in therapy of infectious diseases. Monoclonal antibodies engaged in the treatment of specific cancers seem to work by a dual mode; they mark the cancerous cells for decontamination by the immune system, but also block a function that intervenes with cell growth. The availability of the entire genome sequence of pathogens has strongly facilitated the identification of highly specific protein antigens that are suitable targets for neutralizing antibodies, but also often seem to play an important role in the microbe's life cycle. Thus, the growing repertoire of well-characterized protein antigens will open the perspective to develop monoclonal antibodies against bacterial infections, at least as last resort treatment, when vaccination and antibiotics are no options for prevention or therapy. In the following chapter we describe and compare various technologies regarding the identification of suitable target antigens and the foundation of cognate monoclonal antibodies and discuss their possible applications in the treatment of bacterial infections together with an overview of current efforts.

Darwinian interventions: taming pathogens through evolutionary ecology

From the seemingly inevitable emergence of antibiotic resistance following drug use to the necessity of annual influenza vaccine updates, the ability of pathogens to evolve appears to preclude the development of effective, long-term interventions for many diseases. Despite this gloomy forecast, recent research explores how various principles and concepts from evolutionary ecology might inform practical attempts to bring these disease-causing agents under greater human control. By utilizing evolutionary and ecological information at various scales, these works investigate some promising avenues of disease intervention, from trapping pathogens in evolutionary dead ends, through slowing or inhibiting the process of pathogen adaptation, to more accurate forecasting of pathogen evolutionary trajectories. Thus, an evolutionary ecology perspective might ultimately provide powerful new tools in the pursuit of enduring solutions to the problem of treatment-driven pathogen evolution.

Evolution in health and medicine Sackler colloquium: a public choice framework for controlling transmissible and evolving diseases

Control measures used to limit the spread of infectious disease often generate externalities. Vaccination for transmissible diseases can reduce the incidence of disease even among the unvaccinated, whereas antimicrobial chemotherapy can lead to the evolution of antimicrobial resistance and thereby limit its own effectiveness over time. We integrate the economic theory of public choice with mathematical models of infectious disease to provide a quantitative framework for making allocation decisions in the presence of these externalities. To illustrate, we present a series of examples: vaccination for tetanus, vaccination for measles, antibiotic treatment of otitis media, and antiviral treatment of pandemic influenza.

Predispensing of antivirals to high-risk individuals in an influenza pandemic

We consider the net benefits of predispensing antivirals to high-risk individuals during an influenza pandemic, where the measure of the benefit is the number of severe outcomes (such as deaths or hospitalizations) prevented by antivirals in the whole population. One potential benefit of predispensing is that individuals to whom antivirals have been predispensed may be able to initiate treatment earlier than if they had to wait to obtain and fill a prescription, reducing their risk of progression to severe disease. If this benefit exceeds the side effects of misuse for the category of individuals to whom antivirals were predispensed, and if antiviral supply exceeds overall population demand (which appears relevant for several countries including US in the current H1N1 pandemic), predispensing a quantity of antivirals not exceeding the difference between supply and demand is always beneficial. In this paper we consider the net benefits of predispensing antivirals under various scenarios, including demand exceeding supply, and derive mathematical conditions under which antiviral predispensing is advantageous on balance. For individuals whose relative risk of severe outcome is high enough, such as immunosuppressed individuals (particularly children) and possibly individuals with neurological disorders, predispensing is always beneficial at a given level of antiviral stockpile with modest assumptions on the relative benefit of early treatment by a predispensed course, regardless of the overall population demand for antivirals during the course of an epidemic. Making additional assumptions on either the overall population demand for antivirals (which appear relevant in the current situation) or on the relative benefit of predispensing would make predispensing net beneficial with inclusion of a larger number of persons such as pregnant women and morbidly obese adults.

Prescribing patterns and utilization of antimicrobial drugs in a tertiary care teaching hospital of a Caribbean developing country

This study aimed to evaluate the prescribing practices and utilization of antimicrobials in a tertiary care teaching hospital of a Caribbean developing country. A prospective observational cohort study was undertaken for a period of 12 weeks in the general wards and the intensive care unit (ICU) of the hospital. Demographic data, diagnoses on admission, antimicrobials prescribed, dosage and duration, route of administration, leukocyte count and microbiological culture and sensitivity reports were recorded. Hospital length of stay and final outcome were recorded. The usage was determined in terms of prescribed daily dose and the total costs of antimicrobials were calculated. Of 889 patients admitted, 335 (37.7%) received 22 different antimicrobial drugs. Overall, 67% of the prescriptions adhered to the hospital protocol. Median length of stay in the hospital was 7 days. Skin and soft tissue infections were the most common diagnoses for which antimicrobials were prescribed. Amoxicillin-clavulanate was the most common (32%) antimicrobial used. Eighty-nine percent of the antimicrobials were given through the intravenous route. Sixty percent of the patients received two antimicrobials, 26% received three, and 14% of patients were prescribed four or more antimicrobials during their stay at the hospital. There was significantly higher inappropriate choice of antimicrobials in ICU when compared with general wards (Mantel-Haenszel Odds Ratio 3.3; 95% Confidence Intervals 1.4, 7.7). Prescribing patterns did not strictly adhere to the hospital antimicrobial protocol. There is a need for monitoring and control of antimicrobial prescription.

Identification of Escherichia coli and Salmonella enterica organisms with reduced susceptibility to ceftriaxone from fecal samples of cows in dairy herds

OBJECTIVE

To estimate the relationship between therapeutic use of ceftiofur and recovery of Escherichia coli and Salmonella spp with reduced susceptibility to ceftriaxone from feces of dairy cattle.

ANIMALS

3,840 mature dairy cows on 50 dairy herds in Ohio. Procedures-Fecal samples were obtained from up to 100 mature dairy cows on each farm. Samples were screened for E coli and Salmonella spp with reduced susceptibility to ceftriaxone by use of selective media.

RESULTS

E coli with reduced susceptibility to ceftriaxone was recovered from 92% (46/50) of the herds and 60.9% (2,338/3,840) of cows. Salmonella spp were recovered from 44% (22/50) of the herds and 9.9% (382/3,840) of cows. No association was found between ceftiofur use and recovery of E coli with reduced susceptibility to ceftriaxone at the herd level. However, recovery of E coli with reduced susceptibility to ceftriaxone was more likely from cows in herds in which Salmonella spp were also recovered on the day of collection (odds ratio, 24.96; 95% confidence interval, 3.17 to 196.68) than from herds in which Salmonella spp were not recovered. Odds of recovery of E coli with reduced susceptibility to ceftriaxone from an individual cow increased 62% (odds ratio, 1.62; 95% confidence interval, 1.16 to 2.25) for every 454-kg increase in herd milk production.

CONCLUSIONS AND CLINICAL RELEVANCE

No evidence was found that the use of ceftiofur on dairy farms increases the prevalence or dissemination of Salmonella spp or E coli with reduced susceptibility to ceftriaxone.

Correlation between antibiotic use and resistance in a hospital: temporary and ward-specific observations

OBJECTIVES

The objectives of this study were to determine (1) the increase in antimicrobial resistance to frequently used antibiotics in the hospital setting over time and (2) the correlation between the amount of use of an antibiotic in a specific medical specialty and the observed resistance to that antibiotic in that specialty.

METHOD

The total use of antibiotics and the use of ciprofloxacin (CIP), co-amoxicillin + clavulanic acid (AMCL) and first and second-generation cephalosporins (CEF), respectively, in individual medical specialties were measured between 2001 and 2006 by means of prevalence surveys (two per year). The antimicrobial susceptibility patterns among E. coli isolated from hospitalized patients between 2003 and 2006 were obtained from the Laboratory Information System. Trends over time and correlation between use and resistance were calculated.

RESULTS

6,639 patients were included in the prevalence surveys, of whom 3.0% (195) were treated with CIP, 9.7% (642) with AMCL, and 3.5% (232) with CEF. 4,790 E. coli isolates were obtained from hospitalized patients. Resistance to all antibiotics significantly increased over time, with the regression line showing that the strongest increase in resistance was for CIP (2.6% per year). There were large variations in antimicrobial use between various medical specialties. A significant correlation was found between the ward-specific prevalence of use and the percentage of resistance for CIP (R = 0.81, p < 0.001) and AMCL (R = 0.82, p = 0.003).

CONCLUSION

At the level of individual medical specialties within one hospital, a higher prevalence of antimicrobial use among patients was associated with a significantly higher observed antimicrobial resistance. The use of CIP was associated with a stronger increase in resistance than the use of beta-lactams.

Genodiversity of resistant Pseudomonas aeruginosa isolates in relation to antimicrobial usage density and resistance rates in intensive care units

OBJECTIVE

To evaluate the assumption that resistance rates in intensive care units (ICUs) are markedly influenced by cross-transmission events in addition to high rates of antimicrobial usage.

METHODS

This was a prospective ICU- and laboratory-based surveillance study involving 35 German ICUs from 1999 through 2004. A total of 585 ciprofloxacin- or imipenem-resistant isolates of Pseudomonas aeruginosa were investigated together with resistance rate and unit-based antimicrobial usage density. Antimicrobial use was reported in terms of defined daily doses per 1,000 patient-days. All the strains were assigned to ICU-based genotypes. Genodiversity was calculated as the numbers of indistinguishable ICU-based genotypes found per isolates tested. Reduced ICU-based genodiversity was taken as an indirect measure of frequently occurring cross-transmission events.

RESULTS

The genodiversity of ciprofloxacin- and imipenem-resistant P. aeruginosa isolates was significantly lower (P <=, by Fisher exact test) in ICUs with high resistance rate and low antimicrobial usage density (genodiversity, 0.50 and 0.50, respectively) than in ICUs that featured low resistance rate in the presence of high antimicrobial usage density (genodiversity, 0.90 and 0.95, respectively). In ICUs with low genodiversity, there was a greater rise in resistance rate with increasing antimicrobial usage density, compared with that in ICUs with high diversity.

CONCLUSIONS

This study on resistant P. aeruginosa isolates supports the assumption that high resistance rate in the presence of low antimicrobial usage density results from more-frequent cross-transmission events. A greater rise in resistance rate with increasing antimicrobial usage density in ICUs with low genodiversity indicates that resistance rate in ICUs might be markedly determined by cross-transmission events other than antimicrobial usage.

Impact of antimicrobial usage on the transmission dynamics of antimicrobial resistant bacteria among pigs

There is increasing evidence showing that antimicrobial consumption provides a powerful selective force that promotes the emergence of resistance in pathogenic, commensal as well as zoonotic bacteria in animals. The main aim of this study was to develop a modeling framework that can be used to assess the impact of antimicrobial usage in pigs on the emergence and transmission of resistant bacteria within a finisher pig farm. The transmission dynamics of drug-sensitive and drug-resistant bacteria among pigs in the herd were characterized by studying the local and global stability properties of steady state solutions of the system. Numerical simulations demonstrating the influence of factors such as initial prevalence of infection, presence of pre-existing antimicrobial resistant mutants, and frequency of treatment on predicted prevalence were performed. Sensitivity analysis revealed that two parameters had a huge influence on the predicted proportion of pigs carrying resistant bacteria: (a) the transmission coefficient between uninfected pigs and those infected with drug-resistant bacteria during treatment (beta(2)) and after treatment stops (beta(3)), and (b) the spontaneous clear-out rate of drug-resistant bacteria during treatment (gamma(2)) and immediately after treatment stops (gamma(3)). Control measures should therefore be geared towards reducing the magnitudes of beta(2) and beta(3) or increasing those of gamma(2) and gamma(3).

CD4+T cells do not mediate within-host competition between genetically diverse malaria parasites

Ecological interactions between microparasite populations in the same host are an important source of selection on pathogen traits such as virulence and drug resistance. In the rodent malaria model Plasmodium chabaudi in laboratory mice, parasites that are more virulent can competitively suppress less virulent parasites in mixed infections. There is evidence that some of this suppression is due to immune-mediated apparent competition, where an immune response elicited by one parasite population suppress the population density of another. This raises the question whether enhanced immunity following vaccination would intensify competitive interactions, thus strengthening selection for virulence in Plasmodium populations. Using the P. chabaudi model, we studied mixed infections of virulent and avirulent genotypes in CD4⁺T cell-depleted mice. Enhanced efficacy of CD4⁺T cell-dependent responses is the aim of several candidate malaria vaccines. We hypothesized that if immune-mediated interactions were involved in competition, removal of the CD4⁺T cells would alleviate competitive suppression of the avirulent parasite. Instead, we found no alleviation of competition in the acute phase, and significant enhancement of competitive suppression after parasite densities had peaked. Thus, the host immune response may actually be alleviating other forms of competition, such as that over red blood cells. Our results suggest that the CD4⁺-dependent immune response, and mechanisms that act to enhance it such as vaccination, may not have the undesirable affect of exacerbating within-host competition and hence the strength of this source of selection for virulence.

Effects of therapeutic ceftiofur administration to dairy cattle on Escherichia coli dynamics in the intestinal tract

The goal of this study was to follow ceftiofur-treated and untreated cattle in a normally functioning dairy to examine enteric Escherichia coli for changes in antibiotic resistance profiles and genetic diversity. Prior to treatment, all of the bacteria cultured from the cows were susceptible to ceftiofur. Ceftiofur-resistant E. coli was only isolated from treated cows during and immediately following the cessation of treatment, and the 12 bla(CMY-2)-positive isolates clustered into two genetic groups. E. coli bacterial counts dropped significantly in the treated animals (P < 0.027), reflecting a disappearance of the antibiotic-susceptible strains. The resistant bacterial population, however, did not increase in quantity within the treated cows; levels stayed low and were overtaken by a returning susceptible population. There was no difference in the genetic diversities of the E. coli between the treated and untreated cows prior to ceftiofur administration or after the susceptible population of E. coli returned in the treated cows. A cluster analysis of antibiotic susceptibility profiles resulted in six clusters, two of which were multidrug resistant and were comprised solely of isolates from the treated cows immediately following treatment. The antibiotic treatment provided a window to detect the presence of ceftiofur-resistant E. coli but did not appear to cause its emergence or result in its amplification. The finding of resistant isolates following antibiotic treatment is not sufficient to estimate the strength of selection pressure nor is it sufficient to demonstrate a causal link between antibiotic use and the emergence or amplification of resistance.

Interventions to reduce unnecessary antibiotic prescribing: a systematic review and quantitative analysis

BACKGROUND

Overuse of antibiotics in ambulatory care persists despite many efforts to address this problem. We performed a systematic review and quantitative analysis to assess the effectiveness of quality improvement (QI) strategies to reduce antibiotic prescribing for acute outpatient illnesses for which antibiotics are often inappropriately prescribed.

RESEARCH DESIGN AND METHODS

We searched the Cochrane Collaboration's Effective Practice and Organisation of Care database, supplemented by MEDLINE and manual review of article bibliographies. We included randomized trials, controlled before-after studies, and interrupted time series. Two independent reviewers abstracted all data, and disagreements were resolved by consensus and discussion with a third reviewer. The primary outcome was the absolute reduction in the proportion of patients receiving antibiotics.

RESULTS

Forty-three studies reporting 55 separate trials met inclusion criteria. Most studies (N = 38) addressed prescribing for acute respiratory infections (ARIs). Among the 30 trials eligible for quantitative analysis, the median reduction in the proportion of subjects receiving antibiotics was 9.7% [interquartile range (IQR), 6.6-13.7%] over 6 months median follow-up. No single QI strategy or combination of strategies was clearly superior. However, active clinician education strategies trended toward greater effectiveness than passive strategies (P = 0.096). Compared with studies targeting specific conditions or patient populations, broad-based interventions extrapolated to larger community-level impacts on total antibiotic use, with savings of 17-117 prescriptions per 1000 person-years. Study methodologic quality was fair.

CONCLUSIONS

QI efforts are effective at reducing antibiotic use in ambulatory settings, although much room for improvement remains. Strategies using active clinician education and targeting management of all ARIs (rather than single conditions in single age groups) may yield larger reductions in community-level antibiotic use.

Chemical contaminants in feedlot wastes: concentrations, effects and attenuation

Commercial feedlots for beef cattle finishing are potential sources of a range of trace chemicals which have human health or environmental significance. To ensure adequate protection of human and environmental health from exposure to these chemicals, the application of effective manure and effluent management practices is warranted. The Australian meat and livestock industry has adopted a proactive approach to the identification of best management practices. Accordingly, this review was undertaken to identify key chemical species that may require consideration in the development of guidelines for feedlot manure and effluent management practices in Australia. Important classes of trace chemicals identified include steroidal hormones, antibiotics, ectoparasiticides, mycotoxins, heavy metals and dioxins. These are described in terms of their likely sources, expected concentrations and public health or environmental significance based on international data and research. Androgenic hormones such as testosterone and trenbolone are significantly active in feedlot wastes, but they are poorly understood in terms of fate and environmental implications. The careful management of residues of antibiotics including virginiamycin, tylosin and oxytetracycline appears prudent in terms of minimising the risk of potential public health impacts from resistant strains of bacteria. Good management of ectoparasiticides including synthetic pyrethroids, macrocyclic lactones, fluazuron, and amitraz is important for the prevention of potential ecological implications, particularly towards dung beetles. Very few of these individual chemical contaminants have been thoroughly investigated in terms of concentrations, effects and attenuation in Australian feedlot wastes.

Anti-infective antibodies: a novel tool to prevent and treat nosocomial diseases

The emergence of multidrug-resistant bacteria is a growing challenge for healthcare in the treatment of infectious diseases. In particular, nosocomial infections are getting out of control and reduce the likelihood to recover without, sometimes lethal, complications and long-term damage. Current antibiotics are unable to keep nosocomial infections in check and novel ones move only reluctantly forward and are expected to only delay the problem of multidrug resistance. Progress made in the identification of suitable pathogen targets, a better understanding of host-parasite interactions and the recent inclusion of monoclonal antibodies into the arsenal of novel therapies has provoked the interest to revitalize a historical concept of medicine to treat and prevent bacterial infections with antibodies.

Valuing reduced antibiotic use for pediatric acute otitis media

OBJECTIVE

The 2004 American Academy of Pediatrics acute otitis media guidelines urge parents to weigh the benefits of reduced antibiotic use, adverse drug events, and future resistance versus risks of extra costs and sick days resulting from guideline use. The value of decreased antibiotic resistance has not been quantified. The objective was to perform cost-utility analysis, estimating the resistance value of implementing the guidelines for acute otitis media treatment for children <2 years of age. Outcomes were described with a common denominator and the value of avoiding resistance was estimated using a parental perspective.

METHODS

Decision analysis results were used for outcome probabilities. Published utilities were used to describe outcomes in quality-adjusted life-day units. The minimum resistance benefit value, where the benefits of the American Academy of Pediatrics guidelines would at least balance their costs, was defined as the guidelines' incremental costs minus their other benefits.

RESULTS

For a child 2 to <6 months of age presenting to a primary care physician with possible otitis media, parents would need to value the resistance benefit at 0.77 quality-adjusted life-days per antibiotic prescription avoided for the guidelines' benefits to balance their costs. For the 6- to <24-month-old group, results were 0.67 quality-adjusted life-days per prescription avoided. Results were sensitive to the dollar cost utility; when willingness to pay ranged from $20,000 to $200,000 per quality-adjusted life-year, results ranged from 0.36 and 0.30 quality-adjusted life-days up to 4.10 and 3.57 quality-adjusted life-days for the 2- to <6-month-old and 6- to <24-month-old groups, respectively. Costs were driven by missed parent work days.

CONCLUSIONS

From a societal perspective, trading 0.30 to 4 quality-adjusted life-days to avoid 1 antibiotic course might be desirable; from a parental perspective, this may not be as desirable. Parent demand for antibiotics may be rational when driven by the value of parent time. Other approaches that have the potential to reduce antibiotic use, such as wider use of influenza vaccine and improved rapid viral diagnostic techniques, might be more successful.

Antimicrobial drug use and antibiotic-resistant bacteria

Antimicrobial Drug Use and Antibiotic-Resistant Bacteria (response)

Competitive release and facilitation of drug-resistant parasites after therapeutic chemotherapy in a rodent malaria model

Malaria infections frequently consist of mixtures of drug-resistant and drug-sensitive parasites. If crowding occurs, where clonal population densities are suppressed by the presence of coinfecting clones, removal of susceptible clones by drug treatment could allow resistant clones to expand into the newly vacated niche space within a host. Theoretical models show that, if such competitive release occurs, it can be a potent contributor to the strength of selection, greatly accelerating the rate at which resistance spreads in a population. A variety of correlational field data suggest that competitive release could occur in human malaria populations, but direct evidence cannot be ethically obtained from human infections. Here we show competitive release after pyrimethamine curative chemotherapy of acute infections of the rodent malaria Plasmodium chabaudi in laboratory mice. The expansion of resistant parasite numbers after treatment resulted in enhanced transmission-stage densities. After the elimination or near-elimination of sensitive parasites, the number of resistant parasites increased beyond that achieved when a competitor had never been present. Thus, a substantial competitive release occurred, markedly elevating the fitness advantages of drug resistance above those arising from survival alone. This finding may explain the rapid spread of drug resistance and the subsequently brief useful lifespans of some antimalarial drugs. In a second experiment, where subcurative chemotherapy was administered, the resistant clone was only partly released from competitive suppression and experienced a restriction in the size of its expansion after treatment. This finding raises the prospect of harnessing in-host ecology to slow the spread of drug resistance.

Combating bacteria and drug resistance by inhibiting mechanisms of persistence and adaptation

Antibiotics have revolutionized the treatment of infectious disease but have also rapidly selected for the emergence of resistant pathogens. Traditional methods of antibiotic discovery have failed to keep pace with the evolution of this resistance, which suggests that new strategies to combat bacterial infections may be required. An improved understanding of bacterial stress responses and evolution suggests that in some circumstances, the ability of bacteria to survive antibiotic therapy either by transiently tolerating antibiotics or by evolving resistance requires specific biochemical processes that may themselves be subject to intervention. Inhibiting these processes may prolong the efficacy of current antibiotics and provide an alternative to escalating the current arms race between antibiotics and bacterial resistance. Though these approaches are not clinically validated and will certainly face their own set of challenges, their potential to protect our ever-shrinking arsenal of antibiotics merits their investigation. This Review summarizes the early efforts toward this goal.

Molecular typing of imipenem-resistant Acinetobacter baumannii-calcoaceticus complex in a Singapore hospital where carbapenem resistance is endemic

OBJECTIVE

To investigate the molecular epidemiology of carbapenem-resistant Acinetobacter baumannii-calcoaceticus complex isolates in a tertiary care hospital where the prevalence of carbapenem resistance among these organisms is high.

DESIGN

The study was a prospective, observational study performed during an 8-month period (May 1 through December 31, 2004). A. baumannii isolates recovered from all clinical samples during the study period were included in the study. Antibiotic susceptibility testing was performed using the disk diffusion method, and all carbapenem-resistant strains were typed by a polymerase chain reaction-based typing method.Setting. An 800-bed hospital in Singapore.

RESULTS

More than half of recovered isolates were clonally unrelated, with the remaining isolates grouped into 4 genotypes.

CONCLUSIONS

The results of the study suggest that the high prevalence of carbapenem resistance among Acinetobacter organisms in this institution is not caused by the spread of a predominant clone and that other factors may need to be investigated.

Self-medication with antibiotics in Lithuania

OBJECTIVES

Excessive and not always proper use of antibiotic give rise to numerous problems, of which antimicrobial resistance, currently cause for worldwide concern, is the major one. Few single studies of antibiotic use have been carried out in some countries. This study was performed to estimate the prevalence of antibiotic use in the general population of Lithuania with special interest in self-medication with antibiotics and sources of their acquisition.

MATERIALS AND METHODS

Structured questionnaires on antibiotic use during the last 12 months were mailed to randomly selected adults and 746 of them were finally analyzed.

RESULTS

It was found that 39.9% of respondents reported antibiotic use during the last 12 months preceding the study and 53.2% of those used them in self-medication. In general, 22.0% (95%CI: 19.1-25.1) of respondents used antibiotics without prescription, whereas 45.0% (95%CI: 41.3-48.7) of them used antibiotics for intended self-administration. Adjustment for all the factors revealed the impact of the occupation, place of residence and presence of chronic disease on self-medication with antibiotics. Representatives of managerial, executive and professional occupations used non-prescribed antibiotics 8.38 times more often (95% CI: 1.76-39.91, p = 0.01) than retired people. Healthy people showed the tendency to self-medication 2.04 times more frequently than those with chronic diseases (95%CI: 1.11-3.75, p = 0.02). Rural people used non-prescribed antibiotics 1.79 times more often than inhabitants of urban areas (95%CI: 1.00-3.18, p = 0.049). Community pharmacies proved to be the most frequent (86.0%) source of over-the-counter antibiotics. Tonsillitis, bronchitis, and upper respiratory infections were the major reasons for self-medication with antibiotics.

CONCLUSIONS

The high prevalence of self-medication with antibiotics was found in Lithuania. The study indicated the need for more strict control of antibiotic sales and promotion of education of the correct use of antibiotic among Lithuanian people.

[Evolution of Neisseria meningitidis sensitivity to various antimicrobial drugs over the course of chemoprophylaxis during an epidemic outbreak]

INTRODUCTION

The aim of this study was to assess the evolution of the population MICs for various antimicrobial drugs against Neisseria meningitidis isolates obtained from asymptomatic carriers during a chemoprophylaxis campaign carried out for an epidemic outbreak of meningococcal disease in Nerva, a small town in Huelva province (Spain).

MATERIAL AND METHODS

A nasopharyngeal carrier study including 427 people was carried out to determine the incidence rate of the epidemic strain among the general population. On the basis of the results, chemoprophylaxis with rifampicin was administered to the population aged 15 to 29 years (age group showing the highest incidence of the epidemic strain among carriers) living in Nerva. Three months later a new carrier study was performed (507 people) to evaluate the effects of chemoprophylaxis. Given the evolution of the outbreak, seven months later a new intervention was required with ciprofloxacin chemoprophylaxis; a second carrier study (399 people) was performed two months later to evaluate its effect.

RESULTS

The number of strains isolated during the three carrier studies was 59 (13.8%), 33 (6.5%), and 22 (5.5%), respectively. Analysis of the changes in the MIC50 and MIC90 for the various antibiotics from the first to the second carrier study (rifampicin chemoprophylaxis) showed statistical differences only in the distribution of rifampicin MICs. Similarly, when changes from the second to the third study were analyzed (ciprofloxacin chemoprophylaxis), significant variations were detected for the cefotaxime MICs. Nevertheless, although there were changes in the MICs, the percentages of susceptibility from the beginning to the end of the study did not vary.

CONCLUSIONS

Massive chemoprophylaxis in the age group with the highest incidence of the epidemic strain among carriers did not clearly modify the antibiotic susceptibility of the isolates. However, a slight increase in the MIC50 and MIC90 was observed for rifampicin after the first chemoprophylactic intervention and for cefotaxime at the end of the study. Consecutive chemoprophylactic interventions with rifampicin and ciprofloxacin had an impact on the percentage of meningococcal carriers in the overall population, with a clearly decreasing trend.

The role of compensatory mutations in the emergence of drug resistance

Pathogens that evolve resistance to drugs usually have reduced fitness. However, mutations that largely compensate for this reduction in fitness often arise. We investigate how these compensatory mutations affect population-wide resistance emergence as a function of drug treatment. Using a model of gonorrhea transmission dynamics, we obtain generally applicable, qualitative results that show how compensatory mutations lead to more likely and faster resistance emergence. We further show that resistance emergence depends on the level of drug use in a strongly nonlinear fashion. We also discuss what data need to be obtained to allow future quantitative predictions of resistance emergence.

Can landscape ecology untangle the complexity of antibiotic resistance?

Bacterial resistance to antibiotics continues to pose a serious threat to human and animal health. Given the considerable spatial and temporal heterogeneity in the distribution of resistance and the factors that affect its evolution, dissemination and persistence, we argue that antibiotic resistance must be viewed as an ecological problem. A fundamental difficulty in assessing the causal relationship between antibiotic use and resistance is the confounding influence of geography: the co-localization of resistant bacterial species with antibiotic use does not necessarily imply causation and could represent the presence of environmental conditions and factors that have independently contributed to the occurrence of resistance. Here, we show how landscape ecology, which links the biotic and abiotic factors of an ecosystem, might help to untangle the complexity of antibiotic resistance and improve the interpretation of ecological studies.

Erythromycin for prokinesis: imprudent prescribing?

Problems with antibiotic resistant bacteria are increasing in the hospital and particularly in the intensive care unit. Methicillin-resistant Staphylococcus aureus, Acinetobacter baumanii and extended spectrum beta-lactamase producing Gram-negative bacilli constitute a therapeutic and infection control challenge. Early enteral feeding improves survival in patients in the intensive care unit. Prokinetic agents are routinely used in patients with inappropriate gastrointestinal motility. The use of erythromycin at sub-therapeutic doses as a prokinetic agent is a cause of concern for the following reasons: it can increase the emergence and spread of antibiotic resistance and the likelihood of Clostridium difficile disease. The use of an antibiotic as a prokinetic agent does not constitute prudent antimicrobial prescribing and should be avoided. Alternative agents, whenever possible, should be used.

Healthcare Epidemiology: Potential Confounding in Evaluating Infection‐Control Interventions in Hospital Settings: Changing Antibiotic Prescription

The colonization dynamics of antibiotic-resistant pathogens in hospital settings are complex, with multiple and continuously interacting variables (e.g., introduction of resistance, infection-control practices, antibiotic use). Quantification of these variables is indispensable in the evaluation of intervention studies, because these variables represent potential confounders. In this article, the complexity of colonization dynamics is described. Through a systematic review, we identified studies that evaluated the modification of antibiotic prescription to reduce antibiotic resistance in intensive care units (n=19), and the extent of confounding-control was determined. Most studies evaluated antimicrobial restriction/substitution (n=12) or antibiotic rotation (n=4). Sixteen studies had a prospective cohort design (before-after), of which 12 were without a control group. Introduction of antibiotic resistance was determined in 10 studies. The relative importance of colonization routes and adherence to infection-control measures were not determined in any study. Therefore, it remains uncertain whether observed changes in the prevalence of antibiotic resistance after intervention were causally related to the intervention. Appropriate choices of study design, primary end point (colonization rates rather than infection rates) and statistical tests, determination of colonization routes, and control of potential confounders are needed to increase validity of intervention studies.

Risk factors for recovery of imipenem- or ceftazidime-resistant pseudomonas aeruginosa among patients admitted to a teaching hospital in Brazil

BACKGROUND

The prevalence of resistance to imipenem and ceftazidime among Pseudomonas aeruginosa isolates is increasing worldwide.

OBJECTIVE

Risk factors for nosocomial recovery (defined as the finding of culture-positive isolates after hospital admission) of imipenem-resistant P. aeruginosa (IRPA) and ceftazidime-resistant P. aeruginosa (CRPA) were determined.

DESIGN

Two separate case-control studies were conducted. Control subjects were matched to case patients (ratio, 2:1) on the basis of admission to the same ward at the same time as the case patient. Variables investigated included demographic characteristics, comorbid conditions, and the classes of antimicrobials used.

SETTING

The study was conducted in a 400-bed general teaching hospital in Campinas, Brazil that has 14,500 admissions per year. Case patients and control subjects were selected from persons who were admitted to the hospital during 1992-2002.

RESULTS

IRPA and CRPA isolates were obtained from 108 and 55 patients, respectively. Statistically significant risk factors for acquisition of IRPA were previous admission to another hospital (odds ratio [OR], 4.21 [95% confidence interval {CI}, 1.40-12.66]; P=.01), hemodialysis (OR, 7.79 [95% CI, 1.59-38.16]; P=.01), and therapy with imipenem (OR, 18.51 [95% CI, 6.30-54.43]; P<.001), amikacin (OR, 3.22 [95% CI, 1.40-7.41]; P=.005), and/or vancomycin (OR, 2.48 [95% CI, 1.08-5.64]; P=.03). Risk factors for recovery of CRPA were previous admission to another hospital (OR, 18.69 [95% CI, 2.00-174.28]; P=.01) and amikacin use (OR, 3.69 [95% CI, 1.32-10.35]; P=.01).

CONCLUSION

Our study suggests a definite role for several classes of antimicrobials as risk factors for recovery of IRPA but not for recovery of CRPA. Limiting the use of only imipenem and ceftazidime may not be a wise strategy to contain the spread of resistant P. aeruginosa strains.

Controlling multiple-drug-resistant organisms at the hospital level

Nosocomial infections due to multiple-drug-resistant (MDR) organisms are associated with poor patient outcomes and increased healthcare cost. The natural history of an MDR nosocomial infection can be characterised in four steps. First is the introduction of MDR organisms into the patient's normal flora as a consequence of inappropriate infection control practices. Second is the selection of MDR organisms due, in part, to inappropriate antibiotic therapy. Third is the development of an MDR infection due, in part, to inappropriate invasive techniques. The fourth step occurs when the patient has developed poor clinical outcomes due, in part, to inappropriate antibiotic therapy. At the local hospital level, a multidisciplinary MDR control programme should be developed with the goals to optimise local surveillance of MDR organisms, improve local infection-control practices, and control local antimicrobial use. Without achieving these three goals, hospitals will not be able to control the spread of MDR organisms.

Potential Impacts of Antibiotic Use in Poultry Production

The ways in which antibiotics are used in poultry production have changed considerably during the past decade, mainly because of concerns about potential negative human health consequences caused by these uses. Human health improvements directly attributable to these antibiotic-use changes are difficult to demonstrate. Given that some antibiotics will continue to be used in the poultry industry, methods are needed for estimating the causal relationship between these antibiotic uses and actual animal and human health impacts. This is a challenging task because of the numerous factors that are able to select for the emergence, dissemination, and persistence of antibiotic resistance. Managing the potential impacts of antibiotic use in poultry requires more than a simple estimation of the risks that can be attributed to the use of antibiotics in poultry. Risk models and empirical studies that evaluate interventions that are capable of minimizing the negative consequences associated with specific antibiotic uses are desperately needed.

Beneficial and perverse effects of isoniazid preventive therapy for latent tuberculosis infection in HIV-tuberculosis coinfected populations

In sub-Saharan Africa, where the emergence of HIV has caused dramatic increases in tuberculosis (TB) case notifications, new strategies for TB control are necessary. Isoniazid preventive therapy (IPT) for HIV-TB coinfected individuals reduces the reactivation of latent Mycobacterium tuberculosis infections and is being evaluated as a potential community-wide strategy for improving TB control. We developed a mathematical model of TB/HIV coepidemics to examine the impact of community-wide implementation of IPT for TB-HIV coinfected individuals on the dynamics of drug-sensitive and -resistant TB epidemics. We found that community-wide IPT will reduce the incidence of TB in the short-term but may also speed the emergence of drug-resistant TB. We conclude that community-wide IPT in areas of emerging HIV and drug-resistant TB should be coupled with diagnostic and treatment policies designed to identify and effectively treat the increasing proportion of patients with drug-resistant TB.

Mechanisms by which antibiotics promote dissemination of resistant pneumococci in human populations

Mechanisms by which antimicrobials contribute to dissemination of pneumococcal resistance are incompletely characterized. A serial cross-sectional study of nasopharyngeal pneumococcal carriage in healthy, home-living children <or=6 years of age was conducted in four rural communities-two in Utah (1998-2003) and two in Idaho (2002-2003). Prevalence odds ratios for carriage of resistant pneumococci (OR(res)) and of susceptible pneumococci (OR(sus)) were estimated. Dynamic transmission models were developed to facilitate a mechanistic interpretation of OR(res) and OR(sus) and to compare the population impact of distinct antimicrobial classes. A total of 5,667 cultures were obtained; 25% of the cultures were positive, and 29% of isolates exhibited reduced susceptibility to penicillin. The adjusted OR(res) for recent individual and sibling cephalosporin use was 2.2 (95% confidence interval: 1.4, 3.4) and 1.8 (95% confidence interval: 1.0, 3.3), respectively. Neither individual nor sibling penicillin use was associated with increased OR(res). Rather, recent use of penicillins was associated with decreased carriage of susceptible pneumococci (OR(sus) = 0.2, 95% confidence interval: 0.1, 0.3). In simulations, both types of effects promoted dissemination of resistant pneumococci at the population level. Findings show that oral cephalosporins enhance the risk of acquiring resistant pneumococci. Penicillins accelerate clearance of susceptible strains. The effect of penicillins in increasing resistance is shared equally by treated and untreated members of the population.

Reducing the risk of acquiring antimicrobial-resistant bacteria

Antimicrobial-resistant organisms have become a major issue for all healthcare staff. The Government, media and public are now calling for action to be taken to minimize the risk of acquiring such an infection when admitted to any healthcare setting. Although it is impossible to completely remove the risk of acquiring infection, there are methods already available to healthcare staff and the public that would help to reduce the number of antimicrobial-resistant infections that occur. The National Audit Office (2000) has estimated that if the guidelines already in place were adhered to, the rate of hospital-acquired infections could be reduced by between 15% and 30%. Their use would also help reduce the amount of antimicrobial drugs prescribed and may lower the risk of further development of antimicrobial-resistant microbes. This article examines microbial resistance, sources of infection and discusses the measures that can be taken to reduce the incidence of antimicrobial-resistant infection that occur within the healthcare setting.

Comparison of amoxicillin with alternative agents for the treatment of acute otitis media in children

Expert panels have recommended high-dose amoxicillin (80-90 mg/kg/day) as the therapy of choice for uncomplicated acute otitis media in children. This recommendation is based primarily on pharmacokinetic data predicting bacteriologic cure of most middle ear infections by using amoxicillin at the recommended dosage. However, comparisons of aminopenicillin-containing regimens with alternative treatments, particularly azithromycin, have not consistently demonstrated superiority of the former, even in recent trials with stringent designs. Moreover, amoxicillin exposure may perturb nasopharyngeal colonization more profoundly than do alternative agents. These perturbations may theoretically promote the dissemination of beta-lactam-resistant pneumococci in the community more than other drugs approved for use in otitis media. Such findings suggest that several factors should be considered when choosing an agent to treat otitis media and that reexamination of high-dose amoxicillin as the superior first-line agent for this condition might be warranted.

Pseudomonas aeruginosa, Staphylococcus aureus, and fluoroquinolone use

Increasingly resistant bacteria in sickle cell disease patients indicate need to evaluate extendedspectrum cephalosporin therapy.

Few long-term multicenter investigations have evaluated the relationships between aggregate antimicrobial drug use in hospitals and bacterial resistance. We measured fluoroquinolone use from 1999 through 2003 in a network of US hospitals. The percentages of fluoroquinolone-resistant Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus (MRSA) were obtained from yearly antibiograms at each hospital. Univariate linear regression showed significant associations between a hospital's volume of fluoroquinolone use and percent resistance in most individual study years (1999–2001 for P. aeruginosa, 1999–2002 for S. aureus). When the method of generalized estimating equations was used, a population-averaged longitudinal model incorporating total fluoroquinolone use and the previous year's resistance (to account for autocorrelation) did not show a significant effect of fluoroquinolone use on percent resistance for most drug-organism combinations, except for the relationship between levofloxacin use and percent MRSA. The ecologic relationship between fluoroquinolone use and resistance is complex and requires further study.

A model of antibiotic-resistant bacterial epidemics in hospitals

The emergence of drug-resistant strains of bacteria is an increasing threat to society, especially in hospital settings. Many antibiotics that were formerly effective in combating bacterial infections in hospital patients are no longer effective because of the evolution of resistant strains, which compromises medical care worldwide. In this article, we formulate a two-level population model to quantify key elements in nosocomial (hospital-acquired) infections. At the bacteria level, patients infected with these strains generate both nonresistant and resistant bacteria. At the patient level, susceptible patients are infected by infected patients at rates proportional to the total bacteria load of each strain present in the hospital. The objectives of this paper are to analyze the dynamic elements of nonresistant and resistant bacteria strains in epidemic populations in hospital environments and to provide understanding of measures to avoid the endemicity of resistant antibiotic strains.

Antimicrobial resistance in developing countries. Part I: recent trends and current status

The global problem of antimicrobial resistance is particularly pressing in developing countries, where the infectious disease burden is high and cost constraints prevent the widespread application of newer, more expensive agents. Gastrointestinal, respiratory, sexually transmitted, and nosocomial infections are leading causes of disease and death in the developing world, and management of all these conditions has been critically compromised by the appearance and rapid spread of resistance. In this first part of the review, we have summarised the present state of resistance in these infections from the available data. Even though surveillance of resistance in many developing countries is suboptimal, the general picture is one of accelerating rates of resistance spurred by antimicrobial misuse and shortfalls in infection control and public health. Reservoirs for resistance may be present in healthy human and animal populations. Considerable economic and health burdens emanate from bacterial resistance, and research is needed to accurately quantify the problem and propose and evaluate practicable solutions. In part II, to be published next month, we will review potential containment strategies that could address this burgeoning problem.

Hospital-Level Rates of Fluoroquinolone Use and the Risk of Hospital-Acquired Infection with Ciprofloxacin-Nonsusceptible Pseudomonas aeruginosa

BACKGROUND

In recent years, Pseudomonas aeruginosa has become increasingly resistant to fluoroquinolones, and fluoroquinolone use in the United States has also increased. Our objective was to determine whether higher hospital-level rates of use of ciprofloxacin, levofloxacin, and moxifloxacin antimicrobials were predictors that a higher proportion of P. aeruginosa isolates from hospital-acquired infections (hereafter, "hospital-acquired isolates") would be nonsusceptible to ciprofloxacin.

METHODS

We identified all hospital-acquired isolates from 14 hospitals in the Northern California Kaiser Permanente health care delivery system between 1998 and 2003 and determined their susceptibility to ciprofloxacin. For each facility, we determined the number of days of fluoroquinolone use per 1000 patient-days, by calendar quarter. We used a logistic regression model to analyze the data, with susceptibility status as the outcome variable. Hospital-level rates of use of the 3 fluoroquinolones were the predictors of interest; we adjusted for year, for use of nonquinolone antimicrobials, and for patient variables, including the number of days spent in the hospital in the prior year and fluoroquinolone use in the prior year. The model tested whether isolates from those facilities with higher rates of use of antimicrobials were more likely to be nonsusceptible to ciprofloxacin.

RESULTS

Of 6099 isolates tested, 15% were not susceptible to ciprofloxacin. The nonsusceptibility rate increased from 9% to 20% between 1998 and 2003. Both the overall rate of use at the hospital and prior patient-specific use of ciprofloxacin, levofloxacin, and moxifloxacin were found to be independent predictors that a subsequent P. aeruginosa isolate would be nonsusceptible to ciprofloxacin.

CONCLUSIONS

Higher hospital-level rates of use of ciprofloxacin, levofloxacin, and moxifloxacin are each associated with an increased proportion of hospital-acquired P. aeruginosa isolates being nonsusceptible to ciprofloxacin.