In vitro activity of apramycin (EBL-1003) in combination with colistin, meropenem, minocycline or sulbactam against XDR/PDR Acinetobacter baumannii isolates from Greece.

OBJECTIVES: To evaluate the in vitro activity of the combination of apramycin with colistin, meropenem, minocycline or sulbactam, against some well-characterized XDR Acinetobacter baumannii clinical isolates from Greece, to understand how apramycin can be best incorporated into clinical practice and optimize effectiveness. METHODS: In vitro interactions of apramycin (0.5×, 1× and 2× the MIC value) with colistin (2 mg/L), meropenem (30 mg/L), minocycline (3.5 mg/L) or sulbactam (24 mg/L) were tested using time-kill methodology. Twenty-one clinical A. baumannii isolates were chosen, exhibiting apramycin MICs of 4-16 mg/L, which were at or below the apramycin preliminary epidemiological cut-off value of 16 mg/L. These isolates were selected for a range of colistin (4-32 mg/L), meropenem (16-256 mg/L), minocycline (8-32 mg/L) and sulbactam (8-32 mg/L) MICs across the resistant range. Synergy was defined as a ≥2 log10 cfu/mL reduction compared with the most active agent. RESULTS: The combination of apramycin with colistin, meropenem, minocycline or sulbactam was synergistic, at least at one of the concentrations of apramycin (0.5×, 1× or 2× MIC), against 83.3%, 90.5%, 90.9% or 92.3% of the tested isolates, respectively. Apramycin alone was bactericidal at 24 h against 9.5% and 33.3% of the tested isolates at concentrations equal to 1× and 2× MIC, while the combination of apramycin at 2× MIC with colistin, meropenem or sulbactam was bactericidal against all isolates tested (100%). The apramycin 2× MIC/minocycline combination had bactericidal activity against 90.9% of the tested isolates. CONCLUSIONS: Apramycin combinations may have potential as a treatment option for XDR/pandrug-resistant (PDR) A. baumannii infections and warrant validation in the clinical setting, when this new aminoglycoside is available for clinical use.

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.

Genomic characterization of a KPC-23-producing Klebsiella pneumoniae ST258 clinical isolate resistant to ceftazidime-avibactam.

OBJECTIVES: We characterized the first ceftazidime-avibactam-resistant KPC-producing-Klebsiella pneumoniae clinical isolate detected in Greece, before the introduction of ceftazidime-avibactam in clinical practice. METHODS: K. pneumoniae KP-90 was isolated from a hospitalized patient in Thessaloniki during a nationwide surveillance study conducted between 2014 and 2016. Antimicrobial susceptibility was tested against a panel of agents. Whole-genome sequencing (Ion Torrent TM platform) of the isolate was carried out to identify the acquired resistance genes and mutations that were associated with ceftazidime-avibactam resistance. RESULTS: The K. pneumoniae isolate belonged to multilocus sequence type ST258 and harboured blaKPC-23 as the only carbapenemase gene. The isolate had a minimum inhibitory concentration (MIC) of 16 mg/L to ceftazidime-avibactam and was highly resistant to imipenem, meropenem (MICs, 512 mg/L) and ceftazidime (MIC, >1024 mg/L). blaKPC-23 was detected on a Tn4401a transposon, located on a pKPQIL-type plasmid. A non-functional outer membrane protein OmpK35 and an OmpK36 variant that had been previously associated with K. pneumoniae isolates of ST258 were detected. Transformation studies with Escherichia coli TOP10 showed that KPC-23 offered similar carbapenem MICs as KPC-2 and KPC-3. However, KPC-23 conferred a four-fold higher ceftazidime MIC (>1024 mg/L), which in the presence of avibactam was reduced (>7-fold) to 8 mg/L, which is just within the limit of the susceptibility breakpoint. CONCLUSIONS: Ceftazidime-avibactam resistance in a KPC-23- producing K. pneumoniae clinical isolate was due to increased ceftazidime hydrolysis and was likely enhanced by OmpK35 porin deficiency.

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.

Prevalence of drug resistance among HIV-1 treatment-naive patients in Greece during 2003-2015: Transmitted drug resistance is due to onward transmissions.

BACKGROUND: The prevalence of HIV-1 drug resistance among treatment-naïve patients ranges between 8.3% and 15% in Europe and North America. Previous studies showed that subtypes A and B were the most prevalent in the Greek HIV-1 epidemic. Our aim was to estimate the prevalence of resistance among drug naïve patients in Greece and to investigate the levels of transmission networking among those carrying resistant strains. METHODS: HIV-1 sequences were determined from 3428 drug naïve HIV-1 patients, in Greece sampled during 01/01/2003-30/6/2015. Transmission clusters were estimated by means of phylogenetic analysis including as references sequences from patients failing antiretroviral treatment in Greece and sequences sampled globally. RESULTS: The proportion of sequences with SDRMs was 5.98% (n=205). The most prevalent SDRMs were found for NNRTIs (3.76%), followed by N(t)RTIs (2.28%) and PIs (1.02%). The resistance prevalence was 22.2% based on all mutations associated with resistance estimated using the HIVdb resistance interpretation algorithm. Resistance to NNRTIs was the most common (16.9%) followed by PIs (4.9%) and N(t)RTIs (2.8%). The most frequently observed NNRTI resistant mutations were E138A (7.7%), E138Q (4.0%), K103N (2.3%) and V179D (1.3%). The majority of subtype A sequences (89.7%; 245 out of 273) with the dominant NNRTI resistance mutations (E138A, K103N, E138Q, V179D) were found to belong to monophyletic clusters suggesting regional dispersal. For subtype B, 68.1% (139 out of 204) of resistant strains (E138A, K103N, E138Q V179D) belonged to clusters. For N(t)RTI-resistance, evidence for regional dispersal was found for 27.3% and 21.6% of subtype A and B sequences, respectively. CONCLUSIONS: The TDR rate based on the prevalence of SDRM is lower than the average rate in Europe. However, the prevalence of NNRTI resistance estimated using the HIVdb approach, is high in Greece and it is mostly due to onward transmissions among drug-naïve patients.

High prevalence of the UGT1A1*28 variant in HIV-infected individuals in Greece.

Hyperbilirubinaemia with or without jaundice is one of the side effects of atazanavir boosted with low-dose ritonavir (ATV/rit) related to the drug plasma levels, as a result of its metabolism by UGT1A1 - uridine diphosphate-glucuronosyl transferase. Genotyping for UGT1A1*28 before initiation of antiretroviral therapy containing atazanavir may aid in identifying individuals at risk of hyperbilirubinaemia. Our objective was to estimate the prevalence of the UGTA1A1*28 polymorphism in HIV-infected individuals in Greece and to determine its potential association with hyperbilirubinaemia in patients receiving ATV/rit. The prevalence of the UGTA1A1*28 variant was estimated in 79 HIV-infected patients prior to the administration of the first-line treatment. The UGTA1A1*28 variant was detected in 46 out of 79 individuals (58.2%). Antiretroviral therapy was administered to 64/79 patients (81%). Among them, 26/64 (40.6%) received ATV/rit. Of the ATV/rit-treated patients, 14 were found to be carriers of the UGT1A1*28 variant (54%), and maximum serum bilirubin levels were significantly higher in the carrier population (4.71 vs. 2.69 mg/dL, p = 0.026). In 50% of the population, maximum levels were recorded in the first month of follow-up. Although carriage of UGT1A1 is linked with the development of hyperbilirubinaemia, the implementation of a pharmacogenomic approach in clinical practice cannot yet be recommended as a standard of care.

HIV-1 outbreak among injecting drug users in Greece, 2011: a preliminary report.

A significant increase (more than 10-fold) in the number of newly diagnosed HIV-1 infections among injecting drug users (IDUs) was observed in Greece during the first seven months of 2011. Molecular epidemiology results revealed that a large proportion (96%) of HIV-1 sequences from IDUs sampled in 2011 fall within phylogenetic clusters suggesting high levels of transmission networking. Cases originated from diverse places outside Greece supporting the potential role of immigrant IDUs in the initiation of this outbreak.

Colonization and infection by colistin-resistant Gram-negative bacteria in a cohort of critically ill patients.

In recent years there has been renewed interest in colistin for the treatment of infections by multidrug-resistant Gram-negative bacteria, causing concern that increasing use may be accompanied by the emergence of resistance. This is a retrospective cohort study of colonization and infection by colistin-resistant (CR) gram-negative bacteria in critically ill patients. Colonization data were based on surveillance culture results. Among 150 patients, 78 (52%) were colonized by CR Gram-negative bacteria. Among them, 30 (20%) were colonized by Klebsiella pneumoniae isolates and 51 (34%) were colonized by intrinsically resistant to colistin (CIR) enterobacteriaceae. Seven cases of infection were caused by CR K. pneumoniae and 12 cases by CIR strains. The main risk factor for colonization by CR pathogens was colistin treatment.

Failure of tigecycline to treat severe Clostridium difficile infection.

Clostridium difficile infection is an emerging and often difficult-to-treat iatrogenic complication. Recent data suggest that tigecycline, a novel antibiotic with broad-spectrum antibacterial activity, can be used successfully to treat patients with severe Clostridium difficile infection. We report a 70-year-old man who developed severe Clostridium difficile infection, was admitted to the intensive care unit and eventually succumbed to complications of his illness despite receiving tigecycline for approximately three weeks in combination with vancomycin, metronidazole and intravenous immunoglobulin. Additionally, we discuss the unique challenges that emerged during tigecycline treatment, such as the development of Proteus mirabilis bacteraemia and of colonisation with Acinetobacter baumannii resistant to tigecycline. Finally, we review data on other cases reported in the medical literature. Even though tigecycline looks promising for the treatment of Clostridium difficile infection, we urge caution against its indiscriminate use for off label indications.

Dispensing of antibiotics without prescription in Greece, 2008: another link in the antibiotic resistance chain.

Antibiotic resistance has been associated with the use of antibiotics. The dispensing of antimicrobials without prescription is a potential source of inappropriate antibiotic use. In our study, antibiotics were requested without prescription from pharmacies in the metropolitan area of Athens in Greece in 2008. Twenty-one collaborators visited 174 pharmacies and asked for either amoxicillin/clavulanate acid or ciprofloxacin without providing a prescription or any other justification for the request. In Greece additional restrictions for fluoroquinolone prescriptions were implemented in 2003 after which a separate specific prescription form needs to be filled in by the prescriber, justifying the choice of any fluoroquinolone. Amoxicillin/clavulanate acid was dispensed in all cases. Furthermore, despite the regulation restricting the prescription of ciprofloxacin, this drug was dispensed by 53% of the pharmacies. It appears that the implementation of measures to restrict the use of certain antibiotics (e.g. ciprofloxacin that was studied in our case) was effective in reducing, although not eliminating, inappropriate dispensing. Overall, dispensing of antimicrobials without prescription is a widespread practice in the studied area and is contributing to the overuse of antibiotics.

Successful virological outcome in an HIV-infected individual with a three-class resistant variant and an insertion in the protease genome with a Tipranavir based regimen.

BACKGROUND: Multi-class HIV-1 resistant variants are not rare nowadays. Genotypic and phenotypic resistance testing (including virtual phenotype) constitutes an important tool for optimizing antiretroviral treatment. AIM: To report a case of discrepancy between resistance interpretation and virological outcome. METHODS: A case of a multi-drug experienced patient is presented. Genotypic and/or virtual phenotypic testing analysis was used. RESULTS: The patient after 10 years of antiretroviral therapy with 11 different regimens unable to produce full virological suppression and with a rapidly declining CD4 count, achieved a successful virological outcome with a scheme containing Tipranavir boosted with low dose of ritonavir. Of note, the patient was screened for Tipranavir 1182.48 study and was found ineligible after genotypic analysis. CONCLUSIONS: Virologic suppression was achieved despite the fact that neither an active agent was included in the backbone regimen nor the resistance profile could ensure the effectiveness of Tipranavir.

Outbreaks of zygomycosis in hospitals.

Zygomycosis refers to a group of uncommon and frequently fatal mycoses caused by fungi of the class Zygomycetes, the organisms of which are usually found in decaying organic matter. Disease can be transmitted by the inhalation of spores or by direct inoculation on disrupted skin or mucosa. For rare diseases such as zygomycosis, two or more cases occurring in a short time should be investigated as a probable epidemic. Twelve hospital outbreaks and two pseudoepidemics caused by Zygomycetes have been cited in the English literature. The first epidemic was recorded in 1977 and the last in 2008. Outbreaks have been reported in the USA, the UK and elsewhere in Europe. Cases have included cutaneous, disseminated, pulmonary and rhinocerebral disease. Species identified have included Rhizopus arrhizus, Rhizopus rhizopodiformis, Rhizopus microsporus, Rhizopus spp., Absidia corymbifera and Rhizomucor pusillius. Sources of infection have included Elastoplast adhesive bandage rolls, ventilation systems, wooden tongue depressors, karaya (plant-derived adhesive) ostomy bags, and water damage to a linen store and patient shower room. Patients have included cardiosurgery patients, renal transplant recipients, orthopaedic patients, adult leukaemia patients, intensive care unit neonates, immunocompromised haematology patients, and burn unit patients. Although zygomycosis outbreaks in the hospital environment are infrequent, a high index of suspicion should exist if necrotic lesions appear in proximity to a postoperative wound. Direct tissue examination and tissue culture and histopathology must be routinely performed.

Fluoroquinolone treatment of chronic bacterial prostatitis: a prospective cohort study.

A cohort study of patients (pts) presenting with symptoms of chronic prostatitis over 2 years was performed. Appropriate antimicrobials were administered to confirmed cases of chronic bacterial prostatitis (CBP) after a Stamey-meares (S-M) test for a period of 6 weeks and the test was repeated 1 and 6 months post therapy completion. 145 male patients presented for evaluation. the most prevalent symptoms included dysuria (68%), frequency (38%), and pain which was present in 50%. S-M testing was performed in 69% and expressed prostatic specimen was collected in 53.8%. the diagnosis of CBP was established in 26.9% of the total cohort. Escherichia coli (28.2%) and Enterococcus spp (23.1%) were the most frequently implicated pathogens and ciprofloxacin the most commonly prescribed antimicrobial. A 12-month follow-up was completed in 87% of the pts and 35.3% relapsed a mean of 4.75 months after the initial treatment.

Population pharmacokinetic analysis of colistin methanesulfonate and colistin after intravenous administration in critically ill patients with infections caused by gram-negative bacteria.

Colistin is used to treat infections caused by multidrug-resistant gram-negative bacteria (MDR-GNB). It is administered intravenously in the form of colistin methanesulfonate (CMS), which is hydrolyzed in vivo to the active drug. However, pharmacokinetic data are limited. The aim of the present study was to characterize the pharmacokinetics of CMS and colistin in a population of critically ill patients. Patients receiving colistin for the treatment of infections caused by MDR-GNB were enrolled in the study; however, patients receiving a renal replacement therapy were excluded. CMS was administered at a dose of 3 million units (240 mg) every 8 h. Venous blood was collected immediately before and at multiple occasions after the first and the fourth infusions. Plasma CMS and colistin concentrations were determined by a novel liquid chromatography-tandem mass spectrometry method after a rapid precipitation step that avoids the significant degradation of CMS and colistin. Population pharmacokinetic analysis was performed with the NONMEM program. Eighteen patients (6 females; mean age, 63.6 years; mean creatinine clearance, 82.3 ml/min) were included in the study. For CMS, a two-compartment model best described the pharmacokinetics, and the half-lives of the two phases were estimated to be 0.046 h and 2.3 h, respectively. The clearance of CMS was 13.7 liters/h. For colistin, a one-compartment model was sufficient to describe the data, and the estimated half-life was 14.4 h. The predicted maximum concentrations of drug in plasma were 0.60 mg/liter and 2.3 mg/liter for the first dose and at steady state, respectively. Colistin displayed a half-life that was significantly long in relation to the dosing interval. The implications of these findings are that the plasma colistin concentrations are insufficient before steady state and raise the question of whether the administration of a loading dose would benefit critically ill patients.

Risk-factors and predictors of mortality in patients colonised with vancomycin-resistant enterococci.

Vancomycin-resistant enterococci (VRE) have emerged as significant nosocomial pathogens. A hospital-wide prevalence study was performed to identify cases with VRE faecal colonisation. A case-control study using two randomly selected VRE-negative controls for each positive case was performed to assess risk-factors for VRE colonisation by univariate and multivariate analysis. VRE faecal colonisation was documented in 53 (14.3%) of 370 patients screened. Previous exposure to anti-anaerobic agents, as well as quinolones, was associated with VRE colonisation (p <0.05). The presence of an invasive device (OR 4.8, p 0.003) and the duration of any antimicrobial treatment before VRE isolation (OR 1.2, p <0.001) predicted VRE colonisation in multivariate models. The crude mortality rate for patients with VRE colonisation was 24.5%, but VRE colonisation was not an independent predictor of mortality in these patients. These results suggest that an active surveillance programme focusing on specific patient groups may help in the identification of VRE-colonised patients. Promptly implemented infection control strategies targeting these groups should help to combat the rising incidence of VRE.

Nosocomial vs. community-acquired infective endocarditis in Greece: changing epidemiological profile and mortality risk.

Current epidemiological trends of infective endocarditis (IE) in Greece were investigated via a prospective cohort study of all cases of IE that fulfilled the Duke criteria during 2000-2004 in 14 tertiary and six general hospitals in the metropolitan area of Athens. Demographics, clinical data and outcome were compared for nosocomial IE (NIE) and community-acquired IE (CIE). NIE accounted for 42 (21.5%) and CIE for 153 (78.5%) of 195 cases. Intravenous drug use was associated exclusively with CIE, while co-morbidities (cardiovascular disease, diabetes mellitus, chronic renal failure requiring haemodialysis and malignancies) were more frequent in the NIE group (p <0.05). Prosthetic valve endocarditis (PVE) predominated in the NIE group (p 0.006), and >50% of NIE cases had a history of vascular intervention. Coagulase-negative staphylococci and enterococci were more frequent in cases of NIE than in cases of CIE (26.2% vs. 5.2%, p <0.01, and 30.9% vs. 16.3%, p 0.05, respectively). Enterococci accounted for 19.5% of total IE cases and were the leading cause of NIE. Staphylococcus aureus IE was hospital-acquired in only 11.9% of cases. In-hospital mortality was higher for NIE than for CIE (39.5% vs. 18.6%, p 0.02). Cardiac failure (New York Heart Association grade III-IV; OR 13.3, 95% CI 4.9-36.1, p <0.001) and prosthetic valve endocarditis (OR 3.7, 95% CI 1.3-10.6, p 0.01) were the most important predictors of mortality.

Efficacy and safety of an anti-retroviral combination regimen including either efavirenz or lopinavir-ritonavir with a backbone of two nucleoside reverse transcriptase inhibitors.

The efficacy and safety of a combination regimen including either efavirenz or lopinavir-ritonavir was examined in a cohort of 65 patients positive for human immunodeficiency virus-1 (HIV-1). Both the efavirenz (n = 33, 18 anti-retroviral naive) and lopinavir-ritonavir (n = 32, 15 naive) regimens achieved significant changes from baseline CD4 cell counts and HIV RNA levels after 108 weeks (p < 0.01). Despite diminished immunological and virological parameters at study entry, the lopinavir-ritonavir group showed greater virological effects than the efavirenz group after 108 weeks (median change 3.3 log(10), interquartile range (IQR) 2.2-3.8 log(10) vs. 2.4 log(10), IQR 0.9-3.3 log(10), respectively, p 0.004). Use of lopinavir-ritonavir, in contrast to use of efavirenz, was associated with significant hypertriglyceridaemia.

Thyroid dysfunction in adult long-term survivors after hemapoeitic stem-cell transplantation (HSCT).

Thyroid function was evaluated in 72 adult survivors (41 females and 31 males) at 16 to 56 years of age, 1.5 years mean time (range 0.2 - 9.8) after hemapoeitic stem cell transplantation (HSCT) with no known prior history of thyroid dysfunction. Thyroid stimulating hormone (TSH) and free thyroxin levels (FT4) were determined before and after stimulation with thyrotropin releasing hormone (TRH). Conditioning regimens for HSCT did not include TBI. Overt hypothyroidism (basal TSH > 8 microIU/ml, FT4 < 0.8 ng/dl) was observed in 6% of male patients and 5% of female patients; subclinical hypothyroidism (basal TSH 4 - 8 microIU/ml, low normal FT4 0.8 - 1.9 ng/dl) was observed in 13% of males and 5% of females. A significant number of euthyroid patients (40% males and 54% females) with normal basal TSH and FT4 levels overresponded to TRH stimulation; the finding being statistically significant (p < 0.005). A heavy TSH response after TRH stimulation indicates compensated subclinical dysfunction of the thyroid gland. Chemotherapy-only conditioning regimens may have an adverse effect on thyroid gland function not always detected by determination of basal TSH and FT4 levels. This finding warrants long-term evaluation of thyroid function in HSCT patients.

Prevalence of resistance-associated mutations in newly diagnosed HIV-1 patients in Greece.

The prevalence of HIV-1 drug resistance mutations in naïve patients has been previously shown to differ greatly with the geographic origin. The purpose of this study was to prospectively estimate the prevalence of HIV-1 drug resistance in Greece by analyzing a representative sample of newly HIV-1 diagnosed patients, as part of the SPREAD collaborative study. Protease (PR) and partial reverse transcriptase (RT) sequences were determined from 101 newly diagnosed HIV-1 patients, in Greece, during the period September 2002--August 2003, representing one-third of the total newly diagnosed HIV-1 patients in the same time period. The prevalence of HIV-1 drug resistance was estimated according to the IAS-USA mutation table taking into account all mutations in RT and only major mutations in PR region. The overall prevalence of resistance was 9% [95% confidence interval (CI): 4.2--16.2%]. The prevalence of mutations associated with resistance to NRTIs was 5% (95% CI: 1.6--11.2%), for NNRTIs was 4% (95% CI: 1.1--9.8%), while no major resistance mutations were found in PR. No multi-class resistance was detected in the study population. The prevalence of resistant mutations in the recent seroconverters was 22%. For two individuals, there was clear evidence for transmitted resistance based on epidemiological information for a known source of HIV-1 transmission. The prevalence of the HIV-1 non-B subtypes and recombinants was 52%.