The development and implementation of a guideline-based clinical decision support system to improve empirical antibiotic prescribing

Background

To describe and evaluate a clinical decision support system (CDSS) for empirical antibiotic therapy using a systematic framework.

Methods

A reporting framework for behavior change intervention implementation was used, which includes several domains: development, evaluation and implementation. Within the development domain a description is given of the engagement of stakeholders, a rationale for how the CDSS may influence antibiotic prescribing and a detailed outline of how the system was developed. Within the evaluation domain a technical validation is performed and the interaction between potential users and the CDSS is analyzed. Within the domain of implementation a description is given on how the CDSS was tested in the real world and the strategies that were used for implementation and adoption of the CDSS.

Results

Development: a CDSS was developed, with the involvement of stakeholders, to assist empirical antibiotic prescribing by physicians. Evaluation: Technical problems were determined during the validation process and corrected in a new CDSS version. A usability study was performed to assess problems in the system-user interaction. Implementation: In 114 patients the antibiotic advice that was generated by the CDSS was followed. For 54 patients the recommendations were not adhered to.

Conclusions

This study describes the development and validation of a CDSS for empirical antibiotic therapy and shows the usefulness of the systematic framework for reporting CDSS interventions. In addition it shows that CDSS recommendations are not always adhered to which is associated with incorrect use of the system.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12911-022-01860-3.

Population pharmacokinetics of colistin and the relation to survival in critically ill patients infected with colistin susceptible and carbapenem-resistant bacteria

OBJECTIVES

The aim was to analyse the population pharmacokinetics of colistin and to explore the relationship between colistin exposure and time to death.

METHODS

Patients included in the AIDA randomized controlled trial were treated with colistin for severe infections caused by carbapenem-resistant Gram-negative bacteria. All subjects received a 9 million units (MU) loading dose, followed by a 4.5 MU twice daily maintenance dose, with dose reduction if creatinine clearance (CrCL) < 50 mL/min. Individual colistin exposures were estimated from the developed population pharmacokinetic model and an optimized two-sample per patient sampling design. Time to death was evaluated in a parametric survival analysis.

RESULTS

Out of 406 randomized patients, 349 contributed pharmacokinetic data. The median (90% range) colistin plasma concentration was 0.44 (0.14-1.59) mg/L at 15 minutes after the end of first infusion. In samples drawn 10 hr after a maintenance dose, concentrations were >2 mg/L in 94% (195/208) and 44% (38/87) of patients with CrCL ≤120 mL/min, and >120 mL/min, respectively. Colistin methanesulfonate sodium (CMS) and colistin clearances were strongly dependent on CrCL. High colistin exposure to MIC ratio was associated with increased hazard of death in the multivariate analysis (adjusted hazard ratio (95% CI): 1.07 (1.03-1.12)). Other significant predictors included SOFA score at baseline (HR 1.24 (1.19-1.30) per score increase), age and Acinetobacter or Pseudomonas as index pathogen.

DISCUSSION

The population pharmacokinetic model predicted that >90% of the patients had colistin concentrations >2 mg/L at steady state, but only 66% at 4 hr after start of treatment. High colistin exposure was associated with poor kidney function, and was not related to a prolonged survival.

Oral amoxicillin and amoxicillin-clavulanic acid: properties, indications and usage

BACKGROUND

Amoxicillin has been in use since the 1970s; it is the most widely used penicillin both alone and in combination with the β-lactamase clavulanic acid.

OBJECTIVES

In this narrative review, we re-examine the properties of oral amoxicillin and clavulanic acid and provide guidance on their use, with emphasis on the preferred use of amoxicillin alone.

SOURCES

Published medical literature (MEDLINE database via Pubmed).

CONTENT

While amoxicillin and clavulanic acid have similar half-lives, clavulanic acid is more protein bound and even less heat stable than amoxicillin, with primarily hepatic metabolism. It is also more strongly associated with gastrointestinal side effects, including Clostridium difficile infection, and, thus, in oral combination formulations, limits the maximum daily dose of amoxicillin that can be given. The first ratio for an amoxicillin-clavulanic acid combination was set at 4:1 due to clavulanic acid's high affinity for β-lactamases; ratios of 2:1, 7:1, 14:1 and 16:1 are currently available in various regions. Comparative effectiveness data for the different ratios are scarce. Amoxicillin-clavulanic acid is often used as empiric therapy for many of the World Health Organization's Priority Infectious Syndromes in adults and children, leading to extensive consumption, when some of these syndromes could be handled with a delayed antibiotic prescription approach or amoxicillin alone.

IMPLICATIONS

Using available epidemiological and pharmacokinetic data, we provide guidance on indications for amoxicillin versus amoxicillin-clavulanic acid and on optimal oral administration, including choice of combination ratio. More data are needed, particularly on heat stability, pharmacodynamic effects and emergence of resistance in 'real-world' clinical settings.

How to: EUCAST recommendations on the screening procedure E.Def 10.1 for the detection of azole resistance in Aspergillus fumigatus isolates using four-well azole-containing agar plates

BACKGROUND

The emergence of azole-resistant Aspergillus fumigatus isolates is a matter of significant concern in Europe, with countries reporting resistance rates (which can be as high as 30%) in hospitalized patients. Consequently, the treatment guidelines in The Netherlands, the country with the highest documented prevalence of azole-resistant A. fumigatus, has just been revised to now recommend initial therapy with combination therapy until the susceptibility pattern is known. Therefore, susceptibility testing of clinically relevant isolates has been strongly recommended in the ESCMID-EFISG aspergillosis guidelines. Furthermore, mixed azole-susceptible and azole-resistant (isogenic as well as non-isogenic) infections have been reported to occur, which implies that colonies of clinical cultures may harbour various phenotypes of azole susceptibility.

OBJECTIVES

The EUCAST-AFST (European Committee on Antimicrobial Susceptibility Testing Subcommittee on Antifungal Susceptibility Testing) has released a new screening method document (E.Def 10.1) for the detection of azole-resistant A. fumigatus isolates and updated the QC tables for antifungal susceptibility testing with associated QC endpoints. This review described in detail how to perform the screening test.

SOURCES

This "How to document" is based on the EUCAST azole agar screening method document E.Def 10.1 and the QC tables for antifungal susceptibility testing document, v 2.0 (available at http://www.eucast.org/ast_of_fungi/qcafsttables/) CONTENTS: The method is based on the inoculation of azole-containing and azole-free agars and visual determination of fungal growth after one and two days of incubation. It can easily be implemented in routine laboratories of clinical microbiology and has been validated for simultaneous testing of up to five A. fumigatus colonies using itraconazole and voriconazole (mandatory), and posaconazole (optional).

IMPLICATIONS

This easy-to-use screening procedure for the detection of azole resistance in clinical A. fumigatus isolates will allow rapid testing in the daily routine of the microbiology laboratory and thus facilitate earlier appropriate therapy.

Combining VITEK® 2 with colistin agar dilution screening assist timely reporting of colistin susceptibility

OBJECTIVES

The rise in carbapenem resistance among Gram-negative bacteria has renewed interest in colistin. Recently, the EUCAST-CLSI Polymyxin Breakpoints Working Group declared that broth microdilution (BMD) is the only valid method for colistin susceptibility testing. BMD is not easily incorporated into the routine work of clinical laboratories, and usually this test is incorporated serially, resulting in delayed susceptibility reporting. We tested a strategy of combining VITEK^® 2 with a 2 μg/mL colistin agar dilution (VITEK^® 2/AD) screening plate to improve performance and time to reporting of colistin susceptibility.

METHODS

Colistin susceptibility for 364 clinical isolates was determined by VITEK^® 2/AD and compared with the reference standard BMD according to the ISO 20776-1:2007 and CLSI guidelines. The EUCAST colistin susceptibility breakpoint of ≤2 μg/mL was used. Escherichia coli NCTC 13846 served as quality control strain. Agreement, very major error (VME) and major error rates were determined using ISO 20776-2:2007.

RESULTS

The VME rate for VITEK^® 2 alone was 30.6% (15/49, 95% CI 18.3-45.4%), and was reduced to 10.2% (5/49, 95% CI 3.4-22.2%) using the VITEK^® 2/AD combined testing. The combined testing had categorical agreement with BMD of 97% (354/364, 95% CI 95.0-98.7%), and a major error (ME) rate of 1.6% (5/315, 95% CI 0.5-3.7%). Using the combined testing, even against challenging strains, 349 (95.8%, 95% CI 93.3-97.7%) colistin susceptibility results could be reported, and only 15 isolates required further analysis by BMD.

DISCUSSION

Our method is simple to apply and allows rapid reporting of colistin susceptibility.

Pharmacokinetics and Target Attainment of Ceftobiprole in Asian and Non-Asian Subjects

Ceftobiprole is a broad-spectrum cephalosporin. The objective of this study was to test the hypothesis that the pharmacokinetics (PK) and exposure of ceftobiprole in Asian subjects are similar to those in non-Asian subjects. Three approaches were followed. The first compared the individual PK estimates between the 2 subgroups derived from a population PK model previously built. Next, it was determined whether "Asian subject" was a significant covariate. Finally, a pharmacodynamic analysis was performed by comparing measures of exposure and target attainment. No significant differences were found between PK parameter estimates for Asian and non-Asian subjects, with median values (range) for clearance of 4.82 L/h (2.12-10.47) and 4.97 L/h (0.493-20.6), respectively (P = .736). "Asian subject" was not a significant covariate in the population PK model. There were no significant differences between the measures of exposure. The geometric mean ratio for the fAUC was 1.022 (90%CI, 0.91-1.15), indicating bioequivalence. Taking a target of 60% coverage of the dose interval, more than 90% of the population in both subgroups was adequately exposed. This analysis demonstrated that there are no PK or pharmacodynamic differences between Asian and non-Asian subjects for a ceftobiprole dose of 500 mg every 8 hours as a 2-hour infusion.

Multicentre determination of rezafungin (CD101) susceptibility of Candida species by the EUCAST method

OBJECTIVES

Rezafungin (CD101) is a new long-acting echinocandin allowing weekly dosing, currently undergoing phase-II clinical trials for invasive candidiasis. The aim of this study was to assess rezafungin's in vitro activity against the most frequent Candida species following the EUCAST methodology.

METHODS

The susceptibility of 2018 clinical Candida isolates was determined at four European laboratories. In parallel, six control strains were repeatedly tested. Wild-type upper limits (WT-ULs), defined as the MIC value where the wild-type distribution ends, were determined following the principles for EUCAST ECOFF-setting.

RESULTS

The lowest rezafungin MICs (geometric MIC (GM-MIC), MIC range (mg/L)) were observed for C. albicans (0.016, 0.002-0.125) and the highest for C. parapsilosis (1.657, 0.063->4). MICs for the remaining species were in between these values (GM-MICs 0.048-0.055). Visual and statistical WT-ULs were identical for C. glabrata (0.125), C. krusei (0.125), C. parapsilosis (4), and C. tropicalis (0.25). If adopting these WT-ULs for classification into WT and non-WT populations, 1/413 C. glabrata, 1/402 C. krusei, 1/398 C. parapsilosis, and 1/402 C. tropicalis isolates were categorized as non-WT, all of which derived from Laboratory 1. For C. albicans unexplained laboratory variation was observed (WT-UL: 0.063-0.125 in Laboratories 1 and 2 versus 0.016 in Laboratories 3 and 4). A similar systematic difference was observed comparing the MICs for the three C. albicans QC strains, specifically, obtained in Laboratories 1and 2 with those in Laboratories 3 and 4.

DISCUSSION

Rezafungin displayed species-specific activity similar to other echinocandins. Interlaboratory variation was observed for the most susceptible species C. albicans clinical and QC strains, an observation that warrants further investigation.

Extended-spectrum β-lactamase (ESBL) polymerase chain reaction assay on rectal swabs and enrichment broth for detection of ESBL carriage

BACKGROUND

Extended-spectrum β-lactamase (ESBL) screening and contact precautions on patients at high risk for ESBL carriage are considered important infection control measures. Since contact precautions are costly and may negatively impact patient care, rapid exclusion of ESBL carriage and therefore earlier discontinuation of contact precautions are desired.

AIM

In the present study, the performance of an ESBL polymerase chain reaction (PCR) targeting blaCTX-M genes was evaluated as a screening assay for ESBL carriage.

METHODS

Two methods were assessed: PCR performed directly on rectal swabs and PCR on enrichment broth after incubation overnight. The reference standard was culture of ESBL-producing Enterobacteriaceae on selective agar after overnight enrichment and confirmation by the combination disc diffusion method. Microarray was used for discrepancy analysis. A secondary analysis was performed to evaluate the added value of including a blaSHV target in the PCR.

FINDINGS

A total of 551 rectal swabs from 385 patients were included, of which 28 (5%) were ESBL positive in culture. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were 86%, 98%, 67%, and 99%, respectively, for PCR directly on swabs, and 96%, 98%, 75%, and 100%, respectively, for PCR on enrichment broth. Adding a blaSHV target to the assay resulted in a lower PPV without increasing the sensitivity and NPV.

CONCLUSION

Screening for ESBL by PCR directly on rectal swabs has a high negative predictive value, is up to 48h faster than traditional culture and therefore facilitates earlier discontinuation of contact precautions, thereby improving patient care and saving valuable resources in the hospital.

High interindividual variability in urinary fosfomycin concentrations in healthy female volunteers

OBJECTIVES

Fosfomycin is increasingly being prescribed for treatment of uncomplicated urinary tract infections in an era of emerging drug resistance. Surprisingly, little is known of the urinary concentrations of fosfomycin and its interindividual variation after the standard single 3-g oral dose. We aimed to gain more insight into urinary fosfomycin pharmacokinetics to evaluate its effectiveness.

METHODS

Three grams of fosfomycin trometamol was administered to 40 healthy female volunteers with an estimated mean glomerular filtration rate of >90 mL/min/1.73m². Urine samples were collected from every urination during 48 hours, and then twice daily for up to 7 days. Time, volume, and pH were recorded. Concentrations were quantified with UPLC-MS/MS. Effectiveness was evaluated based on urinary concentrations and the target MIC of E. coli, the most common uropathogen.

RESULTS

A high interindividual variability was found. Peak concentration was 1982.0 ± 1257.4 mg/L, urinary half-life 12.4 ± 5.7 hours, and excretion rate over 48 hours 29.9 ± 7.1 mg/h. Recovery was 44.5 ± 12.6% after 48 hours and 47.0 ± 10.4% after 7 days. Concentrations remained above the EUCAST breakpoint of 32 mg/L in 100% of the volunteers over the first 24 hours, 67.5% for 48 hours, and 30% for 72 hours. A high urinary output was associated with low urinary concentrations and consequently reduced time > MIC, AUC_0-7days/MIC, and C_max/MIC values.

CONCLUSIONS

Considerable interindividual variability observed in the pharmacokinetics of fosfomycin signifies a risk for inadequate drug exposure in a significant proportion of the population. The current dosing regimen should therefore be reevaluated.

[Fosfomycin, an old antibiotic with new possibilities]

- Fosfomycin is a broad-spectrum antibiotic agent used orally for uncomplicated cystitis. The intravenous form of administration has recently been authorised in the Netherlands.- Thanks to its broad spectrum and extensive tissue penetration, fosfomycin offers possibilities for the treatment of infections in different organs.- Infections with multidrug-resistant bacteria pose a significant threat to public health. Many of these multidrug-resistant bacteria are sensitive to fosfomycin, which means fosfomycin may be an option for the treatment of infections with multidrug-resistant bacteria. - There is a lack of knowledge about the pharmacological properties of fosfomycin to establish a good dosing schedule. Knowledge is also lacking about the safety of fosfomycin and the extent of its tolerability in the treatment of different infections. - More research is needed before fosfomycin can be used in the battle against multidrug-resistant bacteria.

Spectrophotometric reading of EUCAST antifungal susceptibility testing of Aspergillus fumigatus

OBJECTIVES

Given the increasing number of antifungal drugs and the emergence of resistant Aspergillus isolates, objective, automated and high-throughput antifungal susceptibility testing is important. The EUCAST E.Def 9.3 reference method for MIC determination of Aspergillus species relies on visual reading. Spectrophotometric reading was not adopted because of concern that non-uniform filamentous growth might lead to unreliable and non-reproducible results. We therefore evaluated spectrophotometric reading for the determination of MICs of antifungal azoles against Aspergillus fumigatus.

METHODS

Eighty-eight clinical isolates of A. fumigatus were tested against four medical azoles (posaconazole, voriconazole, itraconazole, isavuconazole) and one agricultural azole (tebuconazole) with EUCAST E.Def 9.3. The visually determined MICs (complete inhibition of growth) were compared with spectrophotometrically determined MICs and essential (±1 twofold dilution) and categorical (susceptible/intermediate/resistant or wild-type/non-wild-type) agreement was calculated. Spectrophotometric data were analysed with regression analysis using the E_max model, and the effective concentration corresponding to 5% (EC₅) was estimated.

RESULTS

Using the 5% cut-off, high essential (92%-97%) and categorical (93%-99%) agreement (<6% errors) was found between spectrophotometric and visual MICs. The EC₅ also correlated with the visually determined MICs with an essential agreement of 83%-96% and a categorical agreement of 90%-100% (<5% errors).

CONCLUSIONS

Spectrophotometric determination of MICs of antifungal drugs may increase objectivity, and allow automation and high-throughput of EUCAST E.Def 9.3 antifungal susceptibility testing of Aspergillus species.

Nitrofurantoin's efficacy and safety as prophylaxis for urinary tract infections: a systematic review of the literature and meta-analysis of controlled trials

OBJECTIVES

Nitrofurantoin has been used for the prevention of urinary tract infection (UTI) for over 60 years. We conducted a systematic review and meta-analysis to assess its efficacy and safety in the prophylaxis of UTI.

METHODS

We performed a systematic review of all controlled trials in humans assessing nitrofurantoin for UTI prophylaxis published from 1946 to 2015. We further reviewed population-level cohort studies evaluating nitrofurantoin's toxicity. Meta-analyses assessing efficacy and adverse events were conducted on controlled trials.

RESULTS

Twenty-six controlled trials including 3052 patients fulfilled entry criteria for the systematic review and meta-analysis on efficacy and toxicity, and 16 population-level cohort studies were identified for review of toxicity. Overall quality was poor, with all studies at increased risk for various biases. When compared with no prophylaxis, nitrofurantoin is effective in the prevention of UTI (risk ratio 0.38 in favour of nitrofurantoin, 95% CI 0.30-0.48). Its prophylactic efficacy is superior to that of methenamine hippurate and comparable to that of other antibacterials. Compared with patients receiving other antibacterials, those receiving nitrofurantoin had an increased risk of 2.24 (95% CI 1.77-2.83) for a non-severe adverse effect. In all controlled trials, only one patient experienced a severe adverse effect (interstitial pneumonia). Cohort studies reported severe adverse effect frequencies of 0.02-1.5 per 1000 nitrofurantoin users.

CONCLUSIONS

Nitrofurantoin is effective in the prevention of UTI. Its use may be associated with increased non-severe adverse effects; severe adverse effects occur infrequently. The risk of severe toxicity seems to increase with the duration of nitrofurantoin prophylaxis.

Influence of applying different units of measurement on reporting antimicrobial consumption data for pig farms

BACKGROUND

Antimicrobial use in livestock is one of the factors contributing to selection and spread of resistant microorganisms in the environment. National veterinary antimicrobial consumption monitoring programs are therefore in place in a number of countries in the European Union. However, due to differences in methodology, results on veterinary antimicrobial consumption from these national monitoring programs cannot be compared internationally. International comparison is highly needed to establish regulations on veterinary antimicrobial use and reducing antimicrobial resistance. The aim of this study was to assess differences in the outcomes on veterinary antimicrobial consumption by applying three different sets of nationally established animal defined daily dosages to the same antimicrobial drug delivery dataset of Dutch pigs in 2012.

METHODS

Delivery information for the complete Dutch pig sector for the year 2012 reported to the Netherlands Veterinary Medicines Authority (SDa) was analysed with three differently and nationally established animal defined daily dosages from the Netherlands and Denmark: the Defined Daily Dosage AnimalNL (DDDANL), the Animal Daily DosageDK (ADDDK) and Defined Animal Daily DosageDK (DADDDK). For each applied Dutch product equivalent, Danish products were identified based on authorization for pigs, active substance (including form), administration route, concentration and dosage regimen.

RESULTS

Consumption in number of ADDDK/Y was lower than in number of DDDANL/Y for sows/piglets and finisher pigs, with proportions of 83.3 % and 98.3 %. Use in number of DADDDK/Y was even lower, 79.7 % for sows/piglets and 88.1 % for finisher pigs compared to number of DDDANL/Y. At therapeutic group level proportions of number of DADDDK/Y to number of DDDANL/Y were 63.6-150.4 % (sows/piglets) and 55.6-171.0 % (finisher pigs). Proportions were > 100 % for the polymyxines (sows/piglets 150.4 % and finisher pigs 149.9 %) and the macrolides/lincosamides (finisher pigs 171.0 %).

CONCLUSIONS

Differences between nationally established animal defined daily dosages caused by different correction factors for long-acting products and national differences in authorized dosages, have a substantial influence on the results of antimicrobial consumption in pigs. To enable international comparison of veterinary antimicrobial consumption data, harmonized units of measurement, animal weights and animal (sub) categories are needed.

Use of old antibiotics now and in the future from a pharmacokinetic/pharmacodynamic perspective

Because of the increase in bacterial resistance to commonly used antibacterial drugs, old antibiotics are being 'revived' and, once again, are attracting interest. Many of these old antibiotics were approved long ago, in an era when there was no clear process for development, and requirements for efficacy to be demonstrated in rigorous clinical trials did not exist. At the time of these approvals, pharmacokinetic and pharmacodynamic principles were largely unknown, and did not inform the dose-finding process or recommendations for optimal usage. Indeed, the task of generating basic vital information for these old antibiotics remains to be performed. In this review, we provide a brief overview of the most essential data needed for dose justification and optimization. An overview of the shortage of data for selected old antibiotics illustrates the scope of the problem. In order to prevent harming patients with clinical decisions based on inadequate evidence, a redevelopment procedure for old antibiotics is urgently needed, including a regulatory framework.

Identifying targets for quality improvement in hospital antibiotic prescribing

OBJECTIVES

To audit antibiotic use in a university hospital and to identify targets for quality improvement in a setting with low antibiotic use and resistance rates.

METHODOLOGY

A point-prevalence survey (PPS), using a patient-based audit tool for antibiotic use, was executed in the Radboud University Medical Centre in May 2013. On one index day, all patients on systemic antibiotics hospitalised > 24 hours were included. Data regarding antibiotic prescriptions were extracted from the medical records. Multiple logistic regression analysis was performed in order to predict whether a variable was associated with low guideline compliance or a low rate of consulting an infectious disease specialist.

RESULTS

428 hospitalised patients were included, of whom 40.9% received antibiotics. Overall, 75.7% of all prescriptions were compliant with the guidelines in place and for 87.8% the reason for prescription was documented. Amoxicillin/clavulanic acid (OR = 4.08, 95% CI 1.57-10.56), and respiratory tract infections (RTI) (OR = 6.17, 95% CI 2.55-14.94) were associated with low compliance with guidelines. An infectious disease physician or medical microbiologist was less often consulted for empirical therapy (OR 23.21, 95% CI 6.37-84.51) or empirical therapy continued > 72 hours (OR 14.69, 95% CI 3.56-60.56) compared with prescriptions that were based on culture results. In addition, fewer consultations were requested for RTI (OR 4.47, 95% CI 1.39-14.35).

CONCLUSION

A PPS is a good tool to identify targets for antibiotic stewardship in routine clinical practice. Several areas for improvement, such as a low compliance with guidelines for amoxicillin/clavulanic acid and RTI, and a low rate of consulting an infectious disease physician or medical microbiologist concerning antibiotic therapy in case of RTI and empirical therapy continued > 72 hours were identified.

EUCAST expert rules in antimicrobial susceptibility testing

EUCAST expert rules have been developed to assist clinical microbiologists and describe actions to be taken in response to specific antimicrobial susceptibility test results. They include recommendations on reporting, such as inferring susceptibility to other agents from results with one, suppression of results that may be inappropriate, and editing of results from susceptible to intermediate or resistant or from intermediate to resistant on the basis of an inferred resistance mechanism. They are based on current clinical and/or microbiological evidence. EUCAST expert rules also include intrinsic resistance phenotypes and exceptional resistance phenotypes, which have not yet been reported or are very rare. The applicability of EUCAST expert rules depends on the MIC breakpoints used to define the rules. Setting appropriate clinical breakpoints, based on treating patients and not on the detection of resistance mechanisms, may lead to modification of some expert rules in the future.

Dose-response relationships of three amphotericin B formulations in a non-neutropenic murine model of invasive aspergillosis

New lipid-associated formulations of amphotericin B (AmB) have been developed in order to reduce toxicity and enhance the efficacy of AmB by allowing administration of higher doses of the drug. We determined the in vivo dose-response relationships of 1 day and 7 day treatment of AmB, Ambisome (AmBi) and Abelcet (ABLC) in a non-neutropenic murine model of invasive aspergillosis by using survival as an endpoint. Female CD-1 mice were infected intravenously 48 h prior to start therapy with Aspergillus fumigatus (1 x 10(7) conidia/mouse). Groups of 10 mice were treated iv for 1 day or 7 days with increasing 2-fold doses of AmB, ABLC and AmBi up to a maximum of 20 mg/kg/day. Mortality was determined twice daily until day 15. Results were analyzed using product-moment survival analysis and by determining the dose response relationships on day 15. Survival at day 15 of mice with 7 day AmBi or ABLC treatment was significantly better than that of controls or AmB. The ED50s of AmBi and ABLC were 0.06 (95% CI: 0.03-0.127) mg/kg and 0.21 (0.06-0.66) mg/kg respectively. In addition, the maximum effect was higher for AmBi than ABLC, 90% survival versus 68%, respectively. Most of the effects of treatment with AmBi were reached after 1 day of treatment, indicating that the first dose given is most important in predicting survival. This study shows that AmBi and ABLC were significantly more efficacious than AmB in a non-neutropenic murine model of invasive aspergillosis, and that the effect observed was primarily dependent on the first dose administered.

[An outbreak of psittacosis at a bird-fanciers fair in the Netherlands]

Within 2 weeks after a bird-fanciers fair in the Netherlands in November 2007 11 patients presented at our hospital with fever, shivers and severe headache. Dyspnea and dry cough were less common, although the chest X-ray showed a consolidation in 9 out of 11 patients. The clinical diagnosis of psittacosis was quickly confirmed using real-time PCR, although the sensitivity of this test was low (20%). In 9 patients the diagnosis was later confirmed by a rise in complement fixing antibodies in paired sera. None of the patients needed intensive care treatment. All patients recovered uneventfully with antibiotic treatment. Psittacosis is an avian zoonosis, caused by Chlamydophila psittaci. Humans are infected by inhalation of the bacterium that is shedded by excreta or dust from feathers of different sites of either sick or asymptomatic, mostly psittacine, birds. The clinical picture ranges from asymptomatic or mild, flue-like symptoms to severe illness. A timely diagnosis is necessary for successful outbreak management. The realtime PCR is an adequate test in that respect.

Concentration-dependency of beta-lactam-induced filament formation in Gram-negative bacteria

Ceftazidime and cefotaxime are beta-lactam antibiotics with dose-related affinities for penicillin-binding protein (PBP)-3 and PBP-1. At low concentrations, these antibiotics inhibit PBP-3, leading to filament formation. Filaments are long strands of non-dividing bacteria that contain enhanced quantities of endotoxin molecules. Higher concentrations of ceftazidime or cefotaxime cause inhibition of PBP-1, resulting in rapid bacterial lysis, which is associated with low endotoxin release. In the present study, 37 isolates of Escherichia coli, Klebsiella spp., Pseudomonas aeruginosa and Acinetobacter spp. were studied over a 4-h incubation period in the presence of eight concentrations of ceftazidime or cefotaxime. As resistance of Gram-negative bacteria is an emerging problem in clinical practice, 14 isolates of E. coli and Klebsiella pneumoniae that produced extended-spectrum beta-lactamases (ESBLs) were also investigated. Morphological changes after exposure to the beta-lactam antibiotics revealed recognisable patterns in various bacterial families, genera and isolates. In general, all isolates of Enterobacteriaceae produced filaments within a relatively small concentration range, with similar patterns for E. coli and K. pneumoniae. Pseudomonas and Acinetobacter spp. produced filaments in the presence of clinically-relevant concentrations of both antibiotics as high as 50 mg/L. In all genera, filament-producing capacity was clearly related to the MIC. Ceftazidime induced filament production in more isolates and over wider concentration ranges than did cefotaxime. Interestingly, ESBL-producing isolates were not protected against filament induction. The induction of filament production may lead to additional risks during empirical treatment of severe infections.

Role of ceftazidime dose regimen on the selection of resistant Enterobacter cloacae in the intestinal flora of rats treated for an experimental pulmonary infection

OBJECTIVES

The effect of ceftazidime dosing increments and frequency of dosing on the selection of ceftazidime-resistant Enterobacter cloacae in the intestine was studied in rats, during treatment of a pulmonary infection caused by Klebsiella pneumoniae.

METHODS

Rats with pulmonary infection (n = 10 per group) received therapy with doses of ceftazidime at 3.1 to 400 mg/kg per day at a frequency of every 6,12 or 24 h for 18 days, starting 24 h after bacterial inoculation of the lung. Emergence of resistance in intestinal E. cloacae was monitored by culturing fresh stool specimens at days 0, 8, 15, 22, 29, 36 and 43 on agar plates with (6.4 mg/L) and without ceftazidime. Pharmacodynamic indices and time within the mutant selection window (MSW) were assessed in infected rats for each regimen. Ceftazidime-resistant E. cloacae mutants were characterized by determination of the beta-lactamase activity under cefoxitin-induced and non-induced conditions.

RESULTS

A reduction of intestinal ceftazidime-susceptible E. cloacae was observed and showed a significant correlation with the fAUC/MIC at days 8, 15 and 22 and with the fCmax on days 8, 15, 22, 29 and 36. More rats treated with 12-25 and 50-100 mg/kg per day every 6 h were found colonized with ceftazidime-resistant E. cloacae mutants than animals treated every 12 h or every 24 h. The proportion of rats colonized with ceftazidime-resistant E. cloacae mutants at days 15, 36 and 43 correlated with the time during which ceftazidime plasma concentrations were within the boundaries of the MSW. Only at day 15 was a correlation demonstrated between the fCmax and significantly fewer rats colonized with ceftazidime-resistant E. cloacae. Ceftazidime-resistant E. cloacae mutants (MIC >or= 128 mg/L) were characterized as stable derepressed mutants.

CONCLUSIONS

Colonization with stable derepressed ceftazidime-resistant E. cloacae mutants particularly occurred when rats were exposed to moderate doses of ceftazidime (12-25 or 50-100 mg/kg per day) administered every 6 h. Emergence of resistance was correlated with time within the MSW.

Pathophysiology of in-vitro induced filaments, spheroplasts and rod-shaped bacteria in neutropenic mice

This study compared the in-vitro properties and in-vivo effects of Escherichia coli filaments, spheroplasts and normal cells in a murine thigh infection model. E. coli was exposed to ceftazidime, meropenem or saline to obtain filaments, spheroplasts or normal bacilli, which were then injected into neutropenic mice. After 24 h, morphology, CFUs, local and circulating endotoxin levels, cytokine levels and mortality were recorded, and correlations between bacterial and host parameters of infection were investigated. Filaments and spheroplasts contained more endotoxin/CFU than controls. Histological studies showed that morphologically altered bacteria changed into rod-shaped cells in the absence of antibiotics. Bacterial spread to the liver was significantly higher in mice challenged with rod-shaped cells, compared with antibiotic-exposed bacteria (p 0.007). Muscle endotoxin levels correlated significantly with circulating interleukin (IL)-6 and tumour necrosis factor (TNF)-alpha, and both pro-inflammatory cytokines were correlated significantly (p 0.011). Despite a tendency toward higher local and systemic concentrations of endotoxin in the filament group, inflammatory responses and survival did not differ between groups. It was concluded that morphologically altered bacteria contain more endotoxin and can regain a rod shape after withdrawal of antibiotics, while non-antibiotic-exposed bacteria show greater spread to the liver. There was a clear intra-individual relationship between local endotoxin, systemic endotoxin, TNF-alpha and IL-6 production, but these parameters did not differ among groups.

Pharmacokinetics of itraconazole and hydroxyitraconazole in healthy subjects after single and multiple doses of a novel formulation

Originally, itraconazole for parenteral administration was licensed in a 40% hydroxypropyl-beta-cyclodextrin (HPBCD) solution for intravenous administration. A novel formulation, the NanoCrystal formulation (NCF), was prepared. NCF consists of drug particles of approximately 200 to 300 nm. The pharmacokinetics of itraconazole and its hydroxy metabolite in healthy subjects were evaluated after single and multiple doses of itraconazole as NCF. In the single-ascending-dose (SAD) study, itraconazole doses were planned to range from 50 to 500 mg, while in the multiple-ascending-dose (MAD) study, itraconazole doses of 100, 200, and 300 mg as NCF were studied, as was one dose level (200 mg) as an HBPCD solution. Samples were collected in heparinized tubes at various time points and were analyzed by high-performance liquid chromatography to allow full pharmacokinetic analysis both after the first dose and on day 7. The results of both the SAD and the MAD studies indicated that there was a dose dependency in the half-life of itraconazole from the novel formulation, increasing from 44 h (100 mg) to more than 150 h (300 mg) once steady state was achieved. Similar dose-dependent effects were observed for the hydroxy metabolite. The areas under the concentration-time curves for itraconazole and hydroxyitraconazole were also dose dependent. The pharmacokinetic profiles after 200-mg doses of itraconazole as NCF and HPBCD formulations were comparable with respect to the terminal half-life, both after a single dose and at steady state. NCF may provide an alternative to the HPBCD solution for the further optimization of antifungal treatment with itraconazole.

European Committee on Antimicrobial Susceptibility Testing (EUCAST) Technical Notes on antimicrobial susceptibility testing

The main objectives of the European Committee on Antimicrobial Susceptibility Testing (EUCAST) are to harmonise breakpoints for antimicrobial agents in Europe, and to act as the breakpoint committee for the European Medicines Agency (EMEA) during the registration of new antimicrobial agents. Detailed EUCAST procedures for harmonising and setting breakpoints for antimicrobial agents are available on the EUCAST website. Beginning with the current issue, a series of EUCAST Technical Notes will be published in CMI, based on the rationale documents produced by EUCAST for each of the antimicrobial agents studied, with the aim of highlighting important background information underlying decisions on breakpoints made by EUCAST.

Efficacy and pharmacodynamics of flucytosine monotherapy in a nonneutropenic murine model of invasive aspergillosis

The therapeutic efficacy of flucytosine (5FC) monotherapy and the pharmacodynamic index predictive of efficacy were evaluated in a nonneutropenic mouse model of acute invasive aspergillosis. Mice were infected intravenously with an Aspergillus fumigatus isolate (the median MICs of 5FC were 128 mug/ml under the standard condition, 0.5 microg/ml at pH 6.0, and 0.031 microg/ml at pH 5.0) 2 h prior to the start of therapy and were treated for 7 days with different 5FC dosing regimens. The total doses ranged from 50 to 800 mg/kg of body weight/day and were administered at 6-, 12-, and 24-h intervals. The efficacy was assessed by means of survival. The survival rates of the treatment groups ranged from 40 to 90%, while the survival rate of the control group was 20%. The efficacy found depended primarily on the total daily dose. However, the power of our sample size may have been too low to exclude an effect of dose fractionation. The pharmacodynamic index that most strongly correlated with the efficacy was the area under the serum concentration-time curve and MIC ratio (R(2) = 0.86). We conclude that 5FC monotherapy is efficacious in a murine Aspergillus fumigatus infection model.

Relationship between in vitro activities of amphotericin B and flucytosine and pH for clinical yeast and mold isolates

In this study, we investigated the pH dependency of the in vitro activities of amphotericin B (AMB) and flucytosine (5FC) against Candida spp., Cryptococcus neoformans, Aspergillus fumigatus, Rhizopus spp., and Scedosporium prolificans in RPMI 1640 buffered with citrate buffer (pH 4.0, 5.0, 5.4, and 6.0), citrate-phosphate buffer (pH 5.4, 6.0, 6.4, and 7.0), and 3-[N-morpholino]propanesulfonic acid (MOPS) (pH 6.4, 7.0, 7.4, and 7.9). For 5FC, no significant differences were found between MICs obtained with the different buffers, while for AMB, significant differences were found. The MICs obtained with citrate-phosphate buffer were approximately 1 twofold-dilution step higher than the MICs obtained with MOPS. We demonstrated that the in vitro activities of AMB and 5FC against yeast and mold isolates were pH dependent. The in vitro activity of AMB decreased when the pH was lowered, while the in vitro activity of 5FC increased. The effect of the pH on the in vitro activities was dependent not only on the antifungal agent tested but also on the microorganism. For AMB, there was a nonlinear relationship (median r(2), 0.864) for Candida spp., C. neoformans, A. fumigatus, and Rhizopus spp. over the pH range tested. The mean MICs ranged from 0.5 to 2.52 microg/ml at pH 7.0 and from 20.16 to 32 microg/ml at pH 5.0. For S. prolificans, there was no relationship. For 5FC, there was a linear relationship for Candida spp. (median r(2), 0.767) and a nonlinear relationship for C. neoformans and A. fumigatus (median r(2), 0.882) over the pH range tested. The mean MIC values ranged from 0.125 to 1,024 microg/ml at pH 7.0 and from 0.02 to 4 microg/ml at pH 5.0. For Rhizopus spp. and S. prolificans, the relationship could not be determined, since the MIC was >1,024 microg/ml over a pH range of 4.0 to 7.9.

In-vitro susceptibility and molecular characterisation of macrolide resistance mechanisms among Streptococcus pneumonia isolates in The Netherlands: the DUEL 2 study

In total, 881 presumptive clinical isolates of Streptococcus pneumoniae collected from throughout The Netherlands were analysed to determine their mechanisms of macrolide resistance. Isolates were identified initially by participating laboratories using their own standard identification technique, followed by determination of MICs with Etests. Only 797 isolates were confirmed as pneumococci following bile-solubility tests, lytA PCR and 16S rRNA sequencing. Of these confirmed pneumococci, 59 (7.4%) isolates were macrolide-resistant. Analysis by PCR indicated that 34 (57.6%) isolates harboured only the erm(B) gene and 16 (27.1%) only the mef gene. Three (5.1%) isolates carried both erm(B) and mef, while six (10.2%) isolates were negative for both mechanisms. Of the six negative isolates, three had a mutation in the 23S rRNA gene, and three were negative for all mechanisms tested. No isolates with the erm(A) subclass erm(TR) gene were detected. Among the 19 mef-positive isolates, 14 (73.7%) carried the mef(A) gene, and only five (26.3%) carried the mef(E) gene. No linezolid cross-resistance or multiresistance (resistance to more than two classes of antibiotics) was observed.

Which cephalosporin for gonorrhoea?

The recommended treatment for gonorrhoea in the United Kingdom has, until recently, included the fluoroquinolone, ciprofloxacin, which consequently was used by most genitourinary medicine clinics. In 2002 national surveillance data showed that resistance to ciprofloxacin had risen to a prevalence of 9.8% (9% in 2003), indicating that the target of >95% efficacy in first line therapy was no longer achievable. The third generation cephalosporins, ceftriaxone (intramuscular) or cefixime (oral), are the recommended alternatives, but recent audit data reveal other cephalosporins are currently being used to treat gonorrhoea, notably including cefuroxime (intramuscular or, often, oral). A pharmacodynamic analysis was undertaken to determine whether all these regimens were equally potent. Ceftriaxone, 250 (or 500) mg intramuscularly, or cefixime, 400 mg orally, were calculated to give free drug concentrations above the MIC90 for 22-50 hours post dose whereas the cefuroxime regimens being used were pharmacodynamically borderline, achieving this target for only 6.8-11.2 hours and raising the spectre that continued use may select for stepwise increases in resistance, as occurred with penicillin. We therefore underscore that ceftriaxone or cefixime should be the agents of choice to replace ciprofloxacin, as recommended in the new treatment guidelines, and that cefuroxime is a poor substitute.

Effect of pH on the in vitro activities of amphotericin B, itraconazole, and flucytosine against Aspergillus isolates

The in vitro susceptibilities of 21 Aspergillus isolates were tested against three antifungal agents in RPMI 1640 and yeast nitrogen base at pH 5.0 and 7.0 by a broth microdilution format of the NCCLS method. The MICs of amphotericin B and itraconazole were higher, while those of flucytosine were lower, at pH 5.0 than at pH 7.0. The poor correlation between in vitro results and clinical outcome could be due to a difference in pH between the in vitro susceptibility test and at the site of infection.

In vitro interactions between amphotericin B, itraconazole, and flucytosine against 21 clinical Aspergillus isolates determined by two drug interaction models

Combination therapy of flucytosine (5FC) with other antifungal agents could be of use for the treatment of invasive aspergillosis. However, interpretation of the results of in vitro interactions is problematic. The fractional inhibitory concentration (FIC) index is the most commonly used method, but it has several major drawbacks in characterizing antifungal drug interaction. Alternatively, a response surface approach using the concentration-effect relationship over the whole concentration range instead of just the MIC can be used. We determined the in vitro interactions between amphotericin B (AMB), itraconazole, and 5FC against 21 Aspergillus isolates with a broth microdilution checkerboard method that employs the dye MTT [3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide]. FIC indices based on three different MIC endpoints (MIC-0, MIC-1, and MIC-2) and the interaction coefficient alpha were determined, the latter by estimation from the response surface approach described by Greco et al. (W. R. Greco, G. Bravo, and J. C. Parsons, Pharmacol. Rev. 47:331-385, 1995). The value obtained for the FIC index was found to be dependent on the MIC endpoint used and could be either synergistic, indifferent, or antagonistic. The response surface approach gave more consistent results. Of the three combinations tested, the AMB-5FC combination was the most potent in vitro against Aspergillus spp. We conclude that the use of the response surface approach for the interpretation of in vitro interaction studies of antifungals may be helpful in order to predict the nature and intensity of the drug interaction. However, the correlation of these results with clinical outcome remains difficult and needs to be further investigated.

Perioperative pharmacokinetics of cefotaxime in serum and bile during continuous and intermittent infusion in liver transplant patients

BACKGROUND

Drug pharmacokinetics may be altered during liver transplantation. Cefotaxime (CTX), used as perioperative prophylaxis, demonstrates time-dependent killing and therefore continuous infusion might have pharmacodynamic advantages.

OBJECTIVES

To determine the pharmacokinetics of CTX and desacetylcefotaxime (DCTX) in serum, bile and urine during continuous and intermittent infusion when performing liver transplantation.

METHODS

Fifteen patients undergoing liver transplantation were studied after continuous infusion (CI) (4000 mg iv per 24 h following a loading dose of 1000 mg) and intermittent bolus infusion (BI) (1000 mg iv four times daily). Samples were collected during the first 48 h after liver transplantation. Concentrations of CTX and DCTX were determined by HPLC.

RESULTS

During surgery, the mean concentration in serum after CI was 18 mg/L. The lowest serum concentration was 5 mg/L in the CI group and levels were undetectable in the BI group. Target serum concentrations of > or =4 mg/L were reached for 100% of the dosing interval during CI and approximately 60% during BI. Post-operatively, the mean concentration in serum after CI was 26 mg/L. The lowest serum concentration was 8 mg/L in the CI group and levels were undetectable after BI. The peroperative pharmacokinetics of CTX in this patient group were deranged and variable, mainly caused by an increased volume of distribution and decreased hepatic clearance. Metabolism was hampered, but DCTX area under the curve (AUC)/CTX AUC ratios varying between 0.7-0.9 were reached peroperatively. Post-operatively, DCTX AUC/CTX AUC ratios were higher (1.1-1.4). Unchanged CTX in bile was approximately 0.1% of the administered dose, leading to concentrations >4 mg/L throughout the dosing interval for both regimens.

CONCLUSION

Although an intermittent bolus infusion of CTX 1000 mg produces t > target concentration for 60% of the dosing interval during liver transplantation, serum concentrations may be insufficient during the reperfusion phase. Continuous infusion overcomes this. Post-operatively, CTX clearance is impaired by decreased metabolic clearance and there is substantial accumulation of DCTX. In bile, sufficient concentrations of CTX and its active metabolite are reached with both regimens.

Pharmacodynamics of levofloxacin and ciprofloxacin in a murine pneumonia model: peak concentration/MIC versus area under the curve/MIC ratios

During the last decade some studies have shown that the area under the curve (AUC)/MIC ratio is the pharmacodynamic index that best predicts the efficacies of quinolones, while other studies suggest that the predictive value of the peak concentration/MIC (peak/MIC) ratio is superior to the AUC/MIC ratio in explaining clinical and microbiological outcomes. In classical fractionated dose-response studies with animals, it is difficult to differentiate between the AUC/MIC ratio and the peak/MIC ratio because of colinearity. Three different levofloxacin and ciprofloxacin dosing regimens were studied in a neutropenic mouse pneumonia model. The different regimens were used with the aim of increasing the AUC/MIC ratio without changing the peak/MIC ratio and vice versa. The first regimen (RC) consisted of daily doses of 5 up to 160 mg/kg of body weight divided into one, two, or four doses. In the second regimen (R0), mice were given 1.25 mg/kg every hour from 1 to 23 h, while the dose given at 0 h was 2.5, 5, 10, 20, 40, or 80 mg/kg. In the third regimen (R11), mice also received 1.25 mg/kg every hour from 0 to 23 h; but in addition, they also received 2.5, 5, 10, 20, 40, or 80 mg/kg at 11 h. The level of protein binding was also evaluated. The results indicate that the unbound fraction (f(u)) was concentration dependent for both levofloxacin and ciprofloxacin and ranged from approximately 0.67 to 0.88 for both drugs between concentrations of 0.5 and 80 mg/liter. The relationships between the AUC/MIC ratio and the number of CFU were slightly better than those between the peak/MIC ratio and the number of CFU. There was no clear relationship between the amount of time that the concentration remained above the MIC and effect (R(2) < 0.1). For both drugs, the peak/MIC ratio that resulted in a 50% effective concentration was lower for the R0 and R11 dosing regimens, indicating the importance of the AUC/MIC ratio. The same was true for the static doses. Survival studies showed that for mice treated with the low doses the rate of survival was comparable to that for the controls, but with the higher doses the rate of survival was better for mice receiving the R0 regimen. We conclude that for quinolones the AUC/MIC ratio best correlates with efficacy against pneumococci and that the effect of the peak/MIC ratio found in some studies could be partly explained by concentration-dependent protein binding.

Tubal factor pathology caused by Chlamydia trachomatis: the role of serology

One of the causes of infertility in females is tubal pathology as a result of pelvic inflammatory disease (PID) caused by Chlamydia trachomatis (Ct). Diagnosis and identification of patients is hampered by the lack of rapid, easy, sensitive and specific methods. The introduction of Ct-specific enzyme-linked immunosorbent assay (ELISA) tests, based upon synthetic peptides may subsequently increase the sensitivity and specificity for the detection of tubal factor infertility caused by Ct. In order to determine the value of these tests for serological diagnosis of Ct infections, we evaluated several commercially available assays (C. trachomatis enzyme immunoassay (EIA), Labsystems (CtL); SeroCT, Savyon (CtS); pELISA, Medac (CtMp); and a reference assay rELISA, Medac (CtMr)) in two study populations. The first group consisted of 134 female patients with infertility problems. Tubal factor infertility was observed in 85 of these patients (63%). A higher % positivity was found for Ct-specific IgG for the CtL, CtS and CtMp, 41% vs 10%, 57% vs 18% and 55% vs 25% respectively as compared to patients with infertility due to other problems. A similar trend was observed for Ct-specific IgA. The specificity of Ct-specific IgA and IgG in this patient group varied between 92 to 98% and 76 to 90%, respectively. The second group consisted of 107 consecutive gynaecology patients with fertility problems or suspected PID. In this particular patient group, the specificity of the peptide based tests were around 80% and 90% for Ct-specific IgA and 75% and 85% for Ct-specific IgG, respectively. The negative predictive values exceeded 90%, while the positive predictive values varied from 30% to 47% for Ct-specific IgA and was around 30% for Ct-specific IgG. Testing Ct-specific IgG had no additional value above Ct-specific IgA alone. We conclude that the new synthetic peptide-based EIA tests are able to detect species-specific antibodies, which are correlated to (active) infection, and that in particular IgA may be useful in the serodiagnosis of tubal factor infertility caused by C. trachomatis, and will contribute in simplifying the work-up in patients with infertility.

Sensitivity and specificity of three new commercially available Chlamydia trachomatis tests

In order to determine the value of new Chlamydia trachomatis (Ct) specific tests for routine serological diagnosis of Ct infections, we evaluated several commercially available assays (C. trachomatis enzyme immunoassay (EIA), Labsystems (CtL); SeroCT, Savyon (CtS); pELISA, Medac (CtMp)) in various study populations. The prevalence of C. trachomatis-specific IgA antibodies in a blood donor population (n = 443) as determined by the peptide based tests CtL, the CtS and the CtMp was 5%, while for IgG antibodies this was 6% (CtL and CtS) and 12% (CtMp) respectively. Prevalence was negatively correlated with age, concording with C. trachomatis specificity. None of the three tests showed significant titre rises in serum samples taken from patients with a proven infection of Chlamydia pneumoniae (n = 22), indicating species-specificity for all three tests. In patients with a polymerase chain reaction proven (n = 324) Ct infection, 75%, 70% and 68% were positive for IgG and 45%, 38% and 47%, positive for IgA as determined by the CtMp, CtL and CtS respectively. We conclude that the new synthetic peptide-based EIA tests are able to detect species-specific Ct antibodies, which are strongly correlated to (active) infection.